Central heating pump

[sherylryan]

Wondering if someone can answer my queries. We have a firebird C35, downsized to 26kw condensing boiler. 2 Ufh manifolds and rads. When the boiler runs the rads and manifold 50m from boiler the boiler runs perfectly. When the boiler runs the closest manifold 15 m away from boiler heating approx 150sqm floor area, boiler never gets up to temperature, a new pump was fitted running on constant pressure outside of boiler. Pump runs extremely fast on closest manifold, but boiler never gets past 50 degrees. When other manifold and rads are also run with this manifold system runs poorly. Anyone have some ideas for me please.

 

[exedon2]

Pictures of boiler any pipe work - pump -motorised valves - manifolds and a sketch of pipe work layout would be useful.

 

[sherylryan]

Pictures of boiler any pipe work - pump -motorised valves - manifolds and a sketch of pipe work layout would be useful.

Here is a pic of the boiler and the external pump that was fitted, (they run pump at 1.8 bar, constant pressure, variable speed) through to the maze of pipe work. Boiler heats 2 manifolds, manifold one has 10 circuits, 9 on one thermostat heating an area of 160sqm approx, manifold 2 has 8 circuits with 3 thermostats, also runs 15 Radiators and DHW.

 

[John.g]

Here is a pic of the boiler and the external pump that was fitted, (they run pump at 1.8 bar, constant pressure, variable speed) through to the maze of pipe work. Boiler heats 2 manifolds, manifold one has 10 circuits, 9 on one thermostat heating an area of 160sqm approx, manifold 2 has 8 circuits with 3 thermostats, also runs 15 Radiators and DHW.

You say that the "Pump runs extremely fast on closest manifold, but boiler never gets past 50 degrees."
Presume the boiler stat is set at ~ 70C, if so, or if set to anything > 50C, is the burner firing continuously or cycling on/off, if firing continuously then would point to a heating demand > the boiler output of 26kw (unlikely?). Have you got 4 pumps in all, the boiler circ pump + the Grundfos pump shown in photo+ one circ pump each on the UFH manifolds?.

 

[sherylryan]

You say that the "Pump runs extremely fast on closest manifold, but boiler never gets past 50 degrees."
Presume the boiler stat is set at ~ 70C, if so, or if set to anything > 50C, is the burner firing continuously or cycling on/off, if firing continuously then would point to a heating demand > the boiler output of 26kw (unlikely?). Have you got 4 pumps in all, the boiler circ pump + the Grundfos pump shown in photo+ one circ pump each on the UFH manifolds?.

 

[sherylryan]

You say that the "Pump runs extremely fast on closest manifold, but boiler never gets past 50 degrees."
Presume the boiler stat is set at ~ 70C, if so, or if set to anything > 50C, is the burner firing continuously or cycling on/off, if firing continuously then would point to a heating demand > the boiler output of 26kw (unlikely?). Have you got 4 pumps in all, the boiler circ pump + the Grundfos pump shown in photo+ one circ pump each on the UFH manifolds?.

 

[sherylryan]

Correct the boiler does not get up to temperature on the closest manifold circuit but does on the other manifold and rads. The boiler is set at 70 degrees, the boiler runs continuously for an hour then cycles on and off. We only have 3 pumps, they removed the boiler circ Pimp and replaced it with the grundfos in the photo, plus one on each UFH manifold. The pump in the pic, runs at 1.85 bar, when the closest manifold is on it Ramps up to 2500 rpm, when the manifold 55m away comes on pump runs at 1500rpm same when the rads are calling for heat.

 

[John.g]

Is it on the closest manifold that it runs continuously for an hour and then cycles on/off? and is the boiler temperature still only 50C?

Can you post a photo of this 1.85bar pump, this head (18.5M) seems extraordinarily high for a circulation pump, even a 8M pump would be considered high, also please post the exact model number and any other details from the pump label.

 

[sherylryan]

Is it on the closest manifold that it runs continuously for an hour and then cycles on/off? and is the boiler temperature still only 50C?

Can you post a photo of this 1.85bar pump, this head (18.5M) seems extraordinarily high for a circulation pump, even a 8M pump would be considered high, also please post the exact model number and any other details from the pump label.

 

[sherylryan]

Hi John

Yes it is the closest manifold (kitchen), yes after this time the boiler is still sitting anywhere between 45-50 degrees it never reaches boiler set thermostat.

Below is pics of the pump, you will notice in the images of rads and second manifold the rpm’s are quite low. But the kitchen manifold is nearly double the rpms.

The pump is a grundfos CRIE 3-4, pump is set to constant pressure

 

[John.g]

Can't understand the need for a 1.8bar pump, this pump (if it had a bronze casing) would be suitable to pump cold water from a header tank through the secondary heat exchanger of a combi boiler to provide hot water in the event of too low mains pressure.
Used as a circ pump to supply the hot water to a UFH manifold at this head will probably upset the TMV and the ability of the manifold pumps to recirculate water to give the desired mixed water temp as these pumps are generally only 6M pumps like a grundfos UPS3 or the like. It still doesn't explain the boiler running at 26kw, where is the heat going?
Maybe suggest as a temporary measure, reduce the setpoint to something like 0.7bar and see if any inprovement, also have a look at the manifold pumps and see make/model.

 

[sherylryan]

Can't understand the need for a 1.8bar pump, this pump (if it had a bronze casing) would be suitable to pump cold water from a header tank through the secondary heat exchanger of a combi boiler to provide hot water in the event of too low mains pressure.
Used as a circ pump to supply the hot water to a UFH manifold at this head will probably upset the TMV and the ability of the manifold pumps to recirculate water to give the desired mixed water temp as these pumps are generally only 6M pumps like a grundfos UPS3 or the like. It still doesn't explain the boiler running at 26kw, where is the heat going?
Maybe suggest as a temporary measure, reduce the setpoint to something like 0.7bar and see if any inprovement, also have a look at the manifold pumps and see make/model.

Can't understand the need for a 1.8bar pump, this pump (if it had a bronze casing) would be suitable to pump cold water from a header tank through the secondary heat exchanger of a combi boiler to provide hot water in the event of too low mains pressure.
Used as a circ pump to supply the hot water to a UFH manifold at this head will probably upset the TMV and the ability of the manifold pumps to recirculate water to give the desired mixed water temp as these pumps are generally only 6M pumps like a grundfos UPS3 or the like. It still doesn't explain the boiler running at 26kw, where is the heat going?
Maybe suggest as a temporary measure, reduce the setpoint to something like 0.7bar and see if any inprovement, also have a look at the manifold pumps and see make/model.

Can't understand the need for a 1.8bar pump, this pump (if it had a bronze casing) would be suitable to pump cold water from a header tank through the secondary heat exchanger of a combi boiler to provide hot water in the event of too low mains pressure.
Used as a circ pump to supply the hot water to a UFH manifold at this head will probably upset the TMV and the ability of the manifold pumps to recirculate water to give the desired mixed water temp as these pumps are generally only 6M pumps like a grundfos UPS3 or the like. It still doesn't explain the boiler running at 26kw, where is the heat going?
Maybe suggest as a temporary measure, reduce the setpoint to something like 0.7bar and see if any inprovement, also have a look at the manifold pumps and see make/model.

We can’t understand the big pump either. I have attached a photo of the manifold pump, we have just replaced this as we thought it could be the problem. I just attempted to turn pump down and it does nothing but squeal, but the flow water temperature did increase.

 

[John.g]

Definitely a big mismatch there, also the ratio of UFH manifold recirc rate to boiler circ rate will be in the order of ~ up to between 3&5 to 1, for example if you have only one UFH on emitting say 10kw with a mixed flow temp of 45C and return of 38C, the boiler circ pump will only need to supply 4.5LPM at 70C (return 38C) and the manifold pump must recirculate 16.0LPM at 38C, a ratio of 3.6 to 1.

What supplies the DHW demand?.

 

[sherylryan]

Definitely a big mismatch there, also the ratio of UFH manifold recirc rate to boiler circ rate will be in the order of ~ up to between 3&5 to 1, for example if you have only one UFH on emitting say 10kw with a mixed flow temp of 45C and return of 38C, the boiler circ pump will only need to supply 4.5LPM at 70C (return 38C) and the manifold pump must recirculate 16.0LPM at 38C, a ratio of 3.6 to 1.

What supplies the DHW demand?.

I completely understand, it’s so confusing. I wonder if the whole pump set up is wrong. Maybe we will just take this pump out and put original one back in. The boiler can do the DHW but we have it on electric as the boiler is a nightmare.

This big pump was put in because the boiler condensate pipe melted 6 times, so they assumed the boiler circ pump was not big enough. The baffles inside the boiler were disintegrated due to the heat (pic attached) the pump I tuned it down and flow temp increased, flow return dropped dramatically, turn the pump up and the flow temp drops and return increases .

Pic of pump removed from boiler and damaged baffles

 

[John.g]

The plastic melting condensate system was cured by installing a Firebird supplied SS one.
The reason that the 50M run supplied UFH+rads work OK may be because of that long run as, depending on pipe diameter and circ flow probably results in a fair bit of head loss so the head at the manifold is more "normal" then.
I don't really think that the burner is/was actually firing for a hour without any rise in temperature, even if the boiler control stat is faulty, the hi limit stat, would trip/lockout the boiler at ~ 110C.

What diameter is this 50M piping and what are the UFH flow&return temps?

 

[sherylryan]

The plastic melting condensate system was cured by installing a Firebird supplied SS one.
The reason that the 50M run supplied UFH+rads work OK may be because of that long run as, depending on pipe diameter and circ flow probably results in a fair bit of head loss so the head at the manifold is more "normal" then.
I don't really think that the burner is/was actually firing for a hour without any rise in temperature, even if the boiler control stat is faulty, the hi limit stat, would trip/lockout the boiler at ~ 110C.

What diameter is this 50M piping and what are the UFH flow&return temps?

Hi John.
The pipe diameter 33mm copper from boiler until it branches off to manifolds and rads where it drops to 28mm composite pipe before going into 16mm rads and manifold. With boiler thermostat set to 60 degrees Flow at end manifold is 66 degrees, return 54, rads are flow 70 return 55 and trouble manifold is 48/50 flow, 36 return. I timed the boiler heating troubled manifold this afternoon from cold, boiler fired for 93 minutes without stopping only getting to flow temp of 51degrees. Return 36, Thank you.

 

[John.g]

Pipe sizing is not a problem at any rate.

If the boiler cycles on/off with 2XUFH + rads then if the boiler is firing continuously, the excess output must be absorbed somewhere as the problem UFH cannot absorb full boiler output on its own? and with such a slow rise in boiler temp points to the excess output going somewhere else. If the system is not absorbing it the only thing that makes sense to me is that a PRV is lifting somewhere and emitting ~ 8LPM to drain, highly unlikely, would also mean that the boiler has a auto filling system

Theoretically, but this would apply in all modes, if the E.vessel is on the suction side of the pump, then the pump discharge will be 3.6bar (1.8+1.8), don't know if this would lift the PRV or not.

 

[John.g]

Should also have mentioned that you can get a good estimation of the Ufh heat output by adding the total of the flow gauges, LPM, X this X 60 and X by the dT a across the manifold and divide this by 860 to give kW. LPMX60XdT/860 = kW.

 

[sherylryan]

Should also have mentioned that you can get a good estimation of the Ufh heat output by adding the total of the flow gauges, LPM, X this X 60 and X by the dT a across the manifold and divide this by 860 to give kW. LPMX60XdT/860 = kW.

Hi John
Just carried out your calculation and came to 21 kw. I have flushed manifold yesterday thinking it could be full of air, there was abit in one circuit but not bad. I have again stood and watched boiler, while heating troubled manifold, temp rose from 45deg to 58deg in 1/2 hour and sat at 58 for the next hour, return 44. Then turned on Other
manifold and it heated to 66 degrees return 58 in a matter of minutes You are so helpful, thank you.

 

[sherylryan]

Hi John
Just carried out your calculation and came to 21 kw. I have flushed manifold yesterday thinking it could be full of air, there was abit in one circuit but not bad. I have again stood and watched boiler, while heating troubled manifold, temp rose from 45deg to 58deg in 1/2 hour and sat at 58 for the next hour, return 44. Then turned on Other
manifold and it heated to 66 degrees return 58 in a matter of minutes You are so helpful, thank you.

Just had another thought, could the expansion vessel in the boiler be to small? No sure how to calculate total water content of system. Boiler has a 12 litre vessel set to 1 bar.

 

[sherylryan]

Just had another thought, could the expansion vessel in the boiler be to small? No sure how to calculate total water content of system. Boiler has a 12 litre vessel set to 1 bar.

Just had another thought, could the expansion vessel in the boiler be to small? No sure how to calculate total water content of system. Boiler has a 12 litre vessel set to 1 bar.

Hi again, a funny thing happened today, I cheated the system and made the other thermostat on the manifold call for heat and popped the actuators off the other thermostat and believe it or not the boiler heated to 68 degrees although the thermostat is set to 60, why would cheating the system like that work, I thought a thermostat only told the boiler to turn on and off

 

[John.g]

Hi John
Just carried out your calculation and came to 21 kw. I have flushed manifold yesterday thinking it could be full of air, there was abit in one circuit but not bad. I have again stood and watched boiler, while heating troubled manifold, temp rose from 45deg to 58deg in 1/2 hour and sat at 58 for the next hour, return 44. Then turned on Other
manifold and it heated to 66 degrees return 58 in a matter of minutes You are so helpful, thank you.

Good Morning/Night
Are you running the UFH at very high flow/return temps? if not, what are the (mixed) flow/return temps and
what is the flowrate through each loop?

Just had another thought, could the expansion vessel in the boiler be to small? No sure how to calculate total water content of system. Boiler has a 12 litre vessel set to 1 bar.

My basic calculations assume that you are using 100M, 16mm loops which will have a ID of 12mm, a 12mm ID pipe will contain 0.113L/M so total of (9+8)x100x0.113=192L in UFH pipework, say another 85L for the boiler+12 rads = total system contents of 277L. Assume max mean temperature of 60C if whole system in service. At 60C, expansion is 1.62%, a 12L E.Vessel with a precharge pressure & a filling pressure of 1bar will result in a final pressure of 2.2bar, if mean system temperature is 55C, expansion 1.36%, then final pressure is 1.92bar. You should be OK IMO, you can see the boiler pressure with a hot system anyway.

(From water at 15C)
Water
Temp	Exp
Deg.C	%
50	1.124
55	1.36
60	1.62
65	1.83
70	2.18
75	2.48
80	2.8
85	3.13
90	3.49
95	3.85
100	4.24
100	4.64
105	5.05 Hi again, a funny thing happened today, I cheated the system and made the other thermostat on the manifold call for heat and popped the actuators off the other thermostat and believe it or not the boiler heated to 68 degrees although the thermostat is set to 60, why would cheating the system like that work, I thought a thermostat only told the boiler to turn on and off

Strange all right re boiler stat.

 

[sherylryan]

Good Morning/Night
Are you running the UFH at very high flow/return temps? if not, what are the (mixed) flow/return temps and
what is the flowrate through each loop?


My basic calculations assume that you are using 100M, 16mm loops which will have a ID of 12mm, a 12mm ID pipe will contain 0.113L/M so total of (9+8)x100x0.113=192L in UFH pipework, say another 85L for the boiler+12 rads = total system contents of 277L. Assume max mean temperature of 60C if whole system in service. At 60C, expansion is 1.62%, a 12L E.Vessel with a precharge pressure & a filling pressure of 1bar will result in a final pressure of 2.2bar, if mean system temperature is 55C, expansion 1.36%, then final pressure is 1.92bar. You should be OK IMO, you can see the boiler pressure with a hot system anyway.

(From water at 15C)
Water
Temp	Exp
Deg.C	%
50	1.124
55	1.36
60	1.62
65	1.83
70	2.18
75	2.48
80	2.8
85	3.13
90	3.49
95	3.85
100	4.24
100	4.64
105	5.05

Strange all right re boiler stat.

Mixed flow is 48 return is 36/37 on the trouble manifold flow rate is 2.4 lpm per min on 3 loops, 2 litres on 6 loops. When flow meters are opened up fully they never drop to 4 Lpm they only show 3 so not sure if they are reading correctly. Wow you have a lot of knowledge. Thank you very much for all this information.

 

[John.g]

That loop is emitting 16.1kw, you would think all right that the dT might be less at 2.0/2.4LPM, also still doesn't explain why it takes so long to get the temp up to 50C, the loop contains ~ 90L and assuming a cold water temp of 20C, would only require only 3.2kwh so should only take ~ 10/15 minutes as the loops are emitting very little until the flow temperature rises up a bit. If both UFH+rads on then will be very slow to heat up with a boiler output capped to 26kw, should be OK once rooms up to temperature.
You said the pump is noisy when you try to reduce the head, have you actually reduced it or is it still at 1.8bar?, if you post the other UFH details like above, loop flows+ manifold flow/return temps we can see the total flowrate required (with rads i/s as well) and see if the old pump was/is still suitable.

 

[John.g]

Re problem system (again). When you next start it up from cold can you note the individual loop flowrates and the manifold inlet temperature and the mixed manifold and return manifold temperatures especially for the first 10 minutes or so after startup.

 

[John.g]

The manifold inlet temperature and mixed inlet temperature should be the same as the boiler temp until the inlet temp reaches the TMV setpoint.

 

[sherylryan]

That loop is emitting 16.1kw, you would think all right that the dT might be less at 2.0/2.4LPM, also still doesn't explain why it takes so long to get the temp up to 50C, the loop contains ~ 90L and assuming a cold water temp of 20C, would only require only 3.2kwh so should only take ~ 10/15 minutes as the loops are emitting very little until the flow temperature rises up a bit. If both UFH+rads on then will be very slow to heat up with a boiler output capped to 26kw, should be OK once rooms up to temperature.
You said the pump is noisy when you try to reduce the head, have you actually reduced it or is it still at 1.8bar?, if you post the other UFH details like above, loop flows+ manifold flow/return temps we can see the total flowrate required (with rads i/s as well) and see if the old pump was/is still suitable.

 

[sherylryan]

The other manifold only has 3 loops going, one at 1.5 lpm, small laundry loop, 2 other loops at 2 lpm. Flow 45 return 40, out of the 15 rads we only run 9 as the remaining are in rooms not used. Forgot mention this boiler also has 24m of trench heating it is suppose to run as well, (we only use this occasionally)

 

[sherylryan]

I turned the pump down to 1.4 bar that’s the lowest I can get it before it starts cavitating .

 

[John.g]

Ok, thanks, you might just post the two manifold pump modes/settings.

What are your intentions now re above?, do you intend to re install the old pump?.

A lot of experienced installers/posters on here reckon that a low loss header is the way to go with systems like yours. I don't have the experience to comment, have only seen one system with a combined UFH&rad system, my daughters, which has run perfectly for the past 9 years without the LLH, she also has a Firebird 26kw boiler with 10 rads and one ~ 120M2 UFH system, boiler has a ancient 6M grundfos selectric running on speed2 and I think the UFH manifold pump is a grundfos UPS2 (but can't see as it & the manifold are hidden).

 

[sherylryan]

Ok, thanks, you might just post the two manifold pump modes/settings.

What are your intentions now re above?, do you intend to re install the old pump?.

A lot of experienced installers/posters on here reckon that a low loss header is the way to go with systems like yours. I don't have the experience to comment, have only seen one system with a combined UFH&rad system, my daughters, which has run perfectly for the past 9 years without the LLH, she also has a Firebird 26kw boiler with 10 rads and one ~ 120M2 UFH system, boiler has a ancient 6M grundfos selectric running on speed2 and I think the UFH manifold pump is a grundfos UPS2 (but can't see as it & the manifold are hidden).

I believe the pump never needed replaced, the person who installed it use to come out and turn the pump pressure up one week and then the next week he would come and turn it down. This went on for weeks, he turn the pressure up and turned it down. this afternoon the other manifold had a flow at the boiler of 60 and a return of 59 After travelling 110m!! Would the trouble manifold need a bypass on it?

 

[sherylryan]

I believe the pump never needed replaced, the person who installed it use to come out and turn the pump pressure up one week and then the next week he would come and turn it down. This went on for weeks, he turn the pressure up and turned it down. this afternoon the other manifold had a flow at the boiler of 60 and a return of 59 After travelling 110m!! Would the trouble manifold need a bypass on it?

 

[John.g]

Not sure if I am with you, UFH is generally run at temperatures < 50C, say in the 35C to 45C range, so if the TMV is set to 45C and the boiler stat to 70C, then, initially, all the flow through the manifold will be from the boiler with no recirc, once the boiler temperature & TMV are > 45C then the TMV will start recirculating some of the cooler return manifold water to mix with the incoming, eventually, 70C boiler water to maintain that 45C, IMO, even from cold, the troubled UFH, on its own, should reach that 45C in < 15 minutes at the very most. So question remains, is the temperature taking ages to rise even to this 45C or whatever, there is no reason whatsoever IMO as to why it shouldn't. That is why I'm asking to note (again) from cold that UFH manifold (total) flow rate and manifold temperature rise up to say 45C or whatever the TMV is set to. The troubled UFH TMV is set to index 4.8 (48C??), can't see the other one. If the TMV is faulty and on full recirc then the temperature will never rise but the boiler flow temp will and should rise in a few minutes to its setpoint and the burner should cut out.

What are the two pipe stats controlling?, one seems to be set to 60C. They may be wired as safety stats to stop the manifold pump if the manifold temperature rises too high? or maybe shut the zone valve which then tells the manifold pump to stop.

 

[sherylryan]

Not sure if I am with you, UFH is generally run at temperatures < 50C, say in the 35C to 45C range, so if the TMV is set to 45C and the boiler stat to 70C, then, initially, all the flow through the manifold will be from the boiler with no recirc, once the boiler temperature & TMV are > 45C then the TMV will start recirculating some of the cooler return manifold water to mix with the incoming, eventually, 70C boiler water to maintain that 45C, IMO, even from cold, the troubled UFH, on its own, should reach that 45C in < 15 minutes at the very most. So question remains, is the temperature taking ages to rise even to this 45C or whatever, there is no reason whatsoever IMO as to why it shouldn't. That is why I'm asking to note (again) from cold that UFH manifold (total) flow rate and manifold temperature rise up to say 45C or whatever the TMV is set to. The troubled UFH TMV is set to index 4.8 (48C??), can't see the other one. If the TMV is faulty and on full recirc then the temperature will never rise but the boiler flow temp will and should rise in a few minutes to its setpoint and the burner should cut out.

What are the two pipe stats controlling?, one seems to be set to 60C. They may be wired as safety stats to stop the manifold pump if the manifold temperature rises too high? or maybe shut the zone valve which then tells the manifold pump to stop.

Our boiler star has been tuned down to 60 degrees by the tradesman to try and stop the boiler from overheating, and he turned TMV up to 48. I keep asking if there is to be a delta t to around 20 at the boiler for it to condensate it’s not going to work as we have already stated with a boiler temp of 60. They turn the TMV up because they want a higher return to make the boiler condensate. The two pipe stats are wired to the pump to stop it incase of high temperatures.

I will let the boiler cool right down and note the times and flow rates. Thank you for all your help.

 

[John.g]

I can assure you Sheryl that there is absolutely no fear of the boiler overheating even if you run with its max allowable flow temp of 75C or 80C.
Actually the biggest problem with running UFH only is that the boiler return is too LOW, great for condensing effect but bad from a corrosion point of view especially with a OF boiler due to sulphur in the kerosene, problem with a gas fired boiler is that the dT between the boiler flow and return can exceed 30C which is a trip on lots of them. This is one reason for installing a LLH.
On UFH only the UFH return temp IS the boiler return temp.

Example. Boiler flow temp 70C. UFH demand 16kw, UFH flow temp 45C, UFH return temp 35C. The boiler flow (and return) 6.55LPM, 6.55LPM of water at 70C will be mixed with 16.33LPM of recirculated water at 35C to give the required 22.93LPM flow at 45C through the UFH loops.
I will do another calc with radiators i/s as well as UFH.
Schematic may be worth a lot of talking.

 

[John.g]

Boiler Flow temp of 70C. Rad output 10kw combined with ufh of 16kw gives a boiler return of almost 50C.

 

[John.g]

Boiler Flow temp of 60C. Rad output 10kw combined with ufh of 16kw gives a almost perfect boiler return temp of 42.4C which is high enough to prevent corrosion but low enough to give meaningful condensing.

 

[sherylryan]

Boiler Flow temp of 70C. Rad output 10kw combined with ufh of 16kw gives a boiler return of almost 50C.

View attachment 76278

Hi John, interesting reading and out biggest problem is our troubled manifold is running 70% of the time by itself, where are rads are positioned they receive a lot of solar gain. Our troubled manifold is on a thermostat with a 3 degrees difference to turn back in. The biggest problem is thermostat gets up to temp but with 2 hours the sensor has detected the 3. Degrees drop and turns back on. Where does a LLH go on the system, maybe this is our only option. You are very helpful, thank you.

 

[John.g]

What is this thermostat monitoring and where is it fitted or is it a roomstat?

 

[sherylryan]

What is this thermostat monitoring and where is it fitted or is it a roomstat?

The thermostat has a floor probe, Heatmiser neo stat, on the wall in the kitchen.

 

[John.g]

So a ~ 4 hour cycle, 2 hrs on, 2hrs off. I don't see why this should cause any problem in getting the UFH loop temperatures up to set point very rapidly, does it shut a zone valve and the manifold pump?. (No room stat with this?)

 

[sherylryan]

So a ~ 4 hour cycle, 2 hrs on, 2hrs off. I don't see why this should cause any problem in getting the UFH loop temperatures up to set point very rapidly, does it shut a zone valve and the manifold pump?. (No room stat with this?)

The zone valve, pump and boiler all shut down when thermostat reaches temp and tells everything to turn off. I have attached a graph of the flow and return at the boiler, interesting when the boiler is firing temp low, then boiler turns off and pump pumping only temp rises

 

[John.g]

Very interesting, you can see that the boiler return stays very constant at 39C once system up to temperature which is correct as this is the UFH loop return. What would be nice to see is the UFH manifold (mixed) flow temperature during the same period, if you can only monitor two then run the boiler with the boiler flow temp and the manifold mixed temperature. The boiler flow&return were ~ 24C on start up, after 5 mins 40C/27.4C and 70C/39C at burner off after 32 minutes. When circuits up to temperature, then burner cycle time was ~ 12 mins, 6 on, 6 off, so around 13kw average boiler output?.

There are two different requirements here.
one: when on this UFH only, boiler circ pump should stay running continuously with ufh demand and boiler burner cycling on/off.
two: when no demand from UFH, boiler circ pump should also shut down as well as the zone valve and manifold pump, presume this is what is happening?

Once all tests carried out you may consider reducing the manifold temperature from 48C to say 40C which will give longer run times without the (safety) floor sensor acting, even though 2 hours is a reasonable run time. Once steady demand conditions are established (not bad, just now) then the burner on time as a % of the cycle (on/off) times should accurately reflect the UFH & boiler demand. If the burner run time is say 62% of the cycle time then the boiler output is 26*62%, 16kw.

 

[John.g]

Now that I'm fully awake and looking at the trends below, it would seem that the red might be the burner off times and the blue the burner on times, the burner seems to cut out at ~ 72C/75C and cut in at 61C/63C. One way or the other anyway the boiler is maintaining its stat settings so don,t see any big overall problem as long as the UFH flow/return temps are constant and the calculation (LPMx60*dT/860) corresponds to the boiler % cycling time.

 

[sherylryan]

Very interesting, you can see that the boiler return stays very constant at 39C once system up to temperature which is correct as this is the UFH loop return. What would be nice to see is the UFH manifold (mixed) flow temperature during the same period, if you can only monitor two then run the boiler with the boiler flow temp and the manifold mixed temperature. The boiler flow&return were ~ 24C on start up, after 5 mins 40C/27.4C and 70C/39C at burner off after 32 minutes. When circuits up to temperature, then burner cycle time was ~ 12 mins, 6 on, 6 off, so around 13kw average boiler output?.

There are two different requirements here.
one: when on this UFH only, boiler circ pump should stay running continuously with ufh demand and boiler burner cycling on/off.
two: when no demand from UFH, boiler circ pump should also shut down as well as the zone valve and manifold pump, presume this is what is happening?

Once all tests carried out you may consider reducing the manifold temperature from 48C to say 40C which will give longer run times without the (safety) floor sensor acting, even though 2 hours is a reasonable run time. Once steady demand conditions are established (not bad, just now) then the burner on time as a % of the cycle (on/off) times should accurately reflect the UFH & boiler demand. If the burner run time is say 62% of the cycle time then the boiler output is 26*62%, 16kw.

Yes when room stat is up to temp it shuts everything down.
Here is another boiler graph after they downsized the boiler to 26kw

Also this afternoon I watched the boiler start up from cold, 4.02pm start up 32deg, 4.15pm 45 deg, 4.22pm 49deg, pump set to 1.45 bar, 1840rpm, return flow 43.1deg and that’s where it sat for 1 hour

 

[sherylryan]

Now that I'm fully awake and looking at the trends below, it would seem that the red might be the burner off times and the blue the burner on times, the burner seems to cut out at ~ 72C/75C and cut in at 61C/63C. One way or the other anyway the boiler is maintaining its stat settings so don,t see any big overall problem as long as the UFH flow/return temps are constant and the calculation (LPMx60*dT/860) corresponds to the boiler % cycling time.

 

[sherylryan]

Now that I'm fully awake and looking at the trends below, it would seem that the red might be the burner off times and the blue the burner on times, the burner seems to cut out at ~ 72C/75C and cut in at 61C/63C. One way or the other anyway the boiler is maintaining its stat settings so don,t see any big overall problem as long as the UFH flow/return temps are constant and the calculation (LPMx60*dT/860) corresponds to the boiler % cycling time.

No red is the burner firing, blue is the boiler pump circulating only

 

[sherylryan]

The zone valve, pump and boiler all shut down when thermostat reaches temp and tells everything to turn off. I have attached a graph of the flow and return at the boiler, interesting when the boiler is firing

No red is the burner firing, blue is the boiler pump circulating only

temp low, then boiler turns off and pump pumping only temp rises

Yes that’s correct. That’s what I couldn’t understand when carrying out the experiment, why would the temp rise when pump only pumping as opposed to boiler firing and the temp is low

 

[John.g]

OK, confusing signals allright, what UFH output are you getting by doing the calc, above, and what is the time scale on the trends bottom. the boiler would appear to be firing ~ 86.6% of the time, ~ 8.35M on & 1.29M off, this gives a average output of 22.5kw based on a 26kw boiler, how does this compare with the calculated numbers?.
Edit: These tests were carried out last november and the return temp was 50C which means a manifold flow temp of ~ 60C.

Sometime, you might carry out those tests on the healthy system,.

 

[sherylryan]

OK, confusing signals allright, what UFH output are you getting by doing the calc, above, and what is the time scale on the trends bottom. the boiler would appear to be firing ~ 86.6% of the time, ~ 8.35M on & 1.29M off, this gives a average output of 22.5kw based on a 26kw boiler, how does this compare with the calculated numbers?.
Edit: These tests were carried out last november and the return temp was 50C which means a manifold flow temp of ~ 60C.

Sometime, you might carry out those tests on the healthy system,.

Here is a graph of the radiators calling for heat, BLUE IS BOILER FIRING, Red is pump only circulating