Thermal Store Heating Up Cold Feed Pipe

[iainf3]

Hello, I have just installed a vented McDonald 250L thermal store, it is for multi fuel but currently just connected to a standard oil boiler in the garage which is fully pumped to the TS, the system has two pumps both basic 3speed Grunfoss, one on the boiler return and the other on the CH flow both set at the lowest setting.
The F&E tank is in the loft approximately 430mm from the top of the TS to the bottom of the 20litre tank, this in turns uses 15mm cold feed pipe to the bottom of the TS. The expansion is 22mm pipe and run up to approximately 520mm to the top of the bend to the F&E water level.
When on DWH only it works well and heats the tank in no time but when the heating kicks in again heats the radiators effortlessly but starts to heat up the cold feed pipe to the F&E tank. If left on long enough heats it all the way to the tank and assume if left on long enough would heat it as well which is the concern. The 22mm expansion pipe would seem to be sucking in air when this is happening. Attached is a sketch of how it is connected. Any help would be appreciated

 

[ShaunCorbs]

Turn the pump speed down I’m guessing it’s on 3 ?

 

[iainf3]

Turn the pump speed down I’m guessing it’s on 3 ?

Hello, thanks for the reply, both pumps are currently set on their lowest setting #1

 

[Chuck]

Hello, thanks for the reply, both pumps are currently set on their lowest setting #1

What type of pumps are they?

What you describe does seem to suggest that there is an excessive flow-induced pressure gradient between the top and bottom. You might need some method of limiting the flow. I'd make sure the installation complied with the manufacturer's instructions first, and double check that the flow and return connections are the right way round. If all seems okay give them a call to see what they recommend. There maybe a flow deflector inside the tank that's drop off, I don't know, I've never looked inside one and the McDonald website shows artist's impressions rather than technical drawings or photographs of construction.

Of course, a small heat leak up the cold feed is to be expected. It might be worth monitoring the temperature of the expansion tank while the system is running. From it's rate of rise you can infer the power (in watts) that is being wasted. It's only the power that is transferred into the roof (i.e. outside the thermal envelope you are trying to heat) that is really a potential issue.

 

[iainf3]

What type of pumps are they?

What you describe does seem to suggest that there is an excessive flow-induced pressure gradient between the top and bottom. You might need some method of limiting the flow. I'd make sure the installation complied with the manufacturer's instructions first, and double check that the flow and return connections are the right way round. If all seems okay give them a call to see what they recommend. There maybe a flow deflector inside the tank that's drop off, I don't know, I've never looked inside one and the McDonald website shows artist's impressions rather than technical drawings or photographs of construction.

Of course, a small heat leak up the cold feed is to be expected. It might be worth monitoring the temperature of the expansion tank while the system is running. From it's rate of rise you can infer the power (in watts) that is being wasted. It's only the power that is transferred into the roof (i.e. outside the thermal envelope you are trying to heat) that is really a potential issue.

Many thanks for your reply, both are standard Grunfoss 15-50 on the lowest setting. Contacted MacDonald basically there saying this is normal due to expansion with the extra volume in the on the CH circuit, I thought this expansion would be taken up on the expansion pipe which is 22mm but only three metres long and rise 520mm above the F&E tank and not up the cold feed or should say not to the extent that it is heating it up

What type of pumps are they?

What you describe does seem to suggest that there is an excessive flow-induced pressure gradient between the top and bottom. You might need some method of limiting the flow. I'd make sure the installation complied with the manufacturer's instructions first, and double check that the flow and return connections are the right way round. If all seems okay give them a call to see what they recommend. There maybe a flow deflector inside the tank that's drop off, I don't know, I've never looked inside one and the McDonald website shows artist's impressions rather than technical drawings or photographs of construction.

Of course, a small heat leak up the cold feed is to be expected. It might be worth monitoring the temperature of the expansion tank while the system is running. From it's rate of rise you can infer the power (in watts) that is being wasted. It's only the power that is transferred into the roof (i.e. outside the thermal envelope you are trying to heat) that is really a potential issue.

Many thanks for your reply, both are standard Grunfoss 15-50 on the lowest setting. Contacted MacDonald basically there saying this is normal due to thermal expansion with the extra volume in the on the CH circuit, I thought this expansion would be taken up on the expansion pipe which is 22mm but only three metres long and rises 520mm above the F&E tank and not up the cold feed or should say not to the extent that it is heating it up. My man in concern if the heating is running for hours that the expansion which is plastic with a copper float. The wasted heat is not so much of a problem. The only thing that is different from the McDonald layout it’s on 15mm feed pipe as it was it was already there form the original system. I had contacted before do this and it seemingly not an issue to 15mm but can replace with 22mm if required.

 

[Chuck]

My man in concern if the heating is running for hours that the expansion which is plastic with a copper float. The wasted heat is not so much of a problem. The only thing that is different from the McDonald layout it’s on 15mm feed pipe as it was it was already there form the original system. I had contacted before do this and it seemingly not an issue to 15mm but can replace with 22mm if required.

If it's expansion, then a couple of litres of hot water will move up the cold feed into the tank while the radiators are warming but after this transient period, when all the expansion has happened, the extra volume will stay (more of less) in the tank and the feed pipe will cool down.

As with all vented systems, make sure that the inhibitor concentration is regularly checked and topped up if necessary.

 

[John.g]

Many thanks for your reply, both are standard Grunfoss 15-50 on the lowest setting. Contacted MacDonald basically there saying this is normal due to expansion with the extra volume in the on the CH circuit, I thought this expansion would be taken up on the expansion pipe which is 22mm but only three metres long and rise 520mm above the F&E tank and not up the cold feed or should say not to the extent that it is heating it up

Many thanks for your reply, both are standard Grunfoss 15-50 on the lowest setting. Contacted MacDonald basically there saying this is normal due to thermal expansion with the extra volume in the on the CH circuit, I thought this expansion would be taken up on the expansion pipe which is 22mm but only three metres long and rises 520mm above the F&E tank and not up the cold feed or should say not to the extent that it is heating it up. My man in concern if the heating is running for hours that the expansion which is plastic with a copper float. The wasted heat is not so much of a problem. The only thing that is different from the McDonald layout it’s on 15mm feed pipe as it was it was already there form the original system. I had contacted before do this and it seemingly not an issue to 15mm but can replace with 22mm if required.

Have these pumps only got 3 constant speed settings with no additional modes of operation, constant pressure (CP) or/and proportional pressure (PP) modes?.
You are drawing in air with both CH & boiler circ pumps running, if you turn off the CH and let the boiler firing, does the air ingress stop? and vica versa, if you switch off the boiler and let the CH on, does the air ingress stop?.
What is the OF boiler output and does it fire continuously?. Its a multifuel TS, are the oil fired boiler boiler connections correct? and are both pumps pumping in the correct direction?

 

[iainf3]

If it's expansion, then a couple of litres of hot water will move up the cold feed into the tank while the radiators are warming but after this transient period, when all the expansion has happened, the extra volume will stay (more of less) in the tank and the feed pipe will cool down.

As with all vented systems, make sure that the inhibitor concentration is regularly checked and topped up if necessary.

Hello, many thanks for the reply, if it is expansion then I could live with that if the tank is not getting hot. One thing I did try yesterday was to put a double 180 bend (S bend type) in the 15mm cold feed to limit convention of HW to the F&E. tank, is this a waste of time or would it help.
To note form the original thread, is appears to be pulling air in the expansion pipe when this happens or is this just part of the process as the water expands, again no issue on the DWH side only when the CH pumps kicks in. As this was a new addition to a old system when under the floor, I did find tees on the return that are coming from opposing directions eg fighting each other. It worked like that for years but does this cause an imbalance on the CH pipe work?

 

[John.g]

Maybe no harm to help clarify a few items.
The cold feed is actually the cold feed and expansion pipe, the vent pipe which is often termed the expansion pipe will rise in level by exactly the same amount as the the level in the F&E tank (due to U tube effect) but the vast majority of the expansion volume is up through the "cold feed" pipe. My F&E tank dimensions are ~ 381X254x305 MM (LXBXH), with a 30L capacity. Your 250L TS will expand by 8.73L, say 9L, if heated to 90C and 9.63L, say 10L, if heated to 95C. If your F&E tank is similiar to mine with a rise of 10mm/litre then the level in both the vent pipe and the F&E tank will rise by between 90&100 MM, this will have no effect on air ingress. As you state its possibly caused by the Tees, thats why I asked the questions in post #7.

 

[iainf3]

Maybe no harm to help clarify a few items.
The cold feed is actually the cold feed and expansion pipe, the vent pipe which is often termed the expansion pipe will rise in level by exactly the same amount as the the level in the F&E tank (due to U tube effect) but the vast majority of the expansion volume is up through the "cold feed" pipe. My F&E tank dimensions are ~ 381X254x305 MM (LXBXH), with a 30L capacity. Your 250L TS will expand by 8.73L, say 9L, if heated to 90C and 9.63L, say 10L, if heated to 95C. If your F&E tank is similiar to mine with a rise of 10mm/litre then the level in both the vent pipe and the F&E tank will rise by between 90&100 MM, this will have no effect on air ingress. As you state its possibly caused by the Tees, thats why I asked the questions in post #7.

Many Thanks again, I missed post #7 these are old Grunfos pumps 15/50 3 speed no propositional control, the CH is approx. 25 years old and the boiler 15. The expansion is tank is the original 20 litre unit which used to supply a Grant back boiler and a Stanley oil fired cooker through neutralizer, the solid fuel was removed and the Stanley replaced with conventional Boulter 60-90 boiler on lowest setting supplying 160ltre indirect tank approximately 15 years, A month ago, the neutralizer and tank where all removed and replaced with the TS with the OFB set to 70DegC, stated in the McDonald instruction, as mentioned when on DWH seems little issue no air moving and little expansion to the tank and heats the TS in no time.

This morning I did a test to measure the expansion with the TS hot from the DWH running, I turned on the CH pump and you can then hear some air movement on the expansion pipe and after a wee while at which time the radiators are hot the tank has expanded up approx. and 1.5”

The TS works extremely well compare to what there before and heats in no time and the thermostat in the hall turned off at 20Deg at which time stops both pump and the boiler, What I did notice when this happened, the cold pipe went cold to the TS very quickly. Attached is the schematic from McD showing the connections and only is mine use the 15mm connection for the cold feed rather than the 22mm as it was there for the neutralizer system of old. Regarding the tee under the floor on the CH return that seem to be fighting each other should this be replaced or will make little difference
Regarding connections to the TS please see attached.

 

[John.g]

If you just turn on the CH only, (shut down the boiler), do you still hear/get air problems?

The boiler stat is set to 70C?, what is the TS stat set to?.

Are those Grundfos pumps the old Selectric type?.

 

[iainf3]

If you just turn on the CH only, (shut down the boiler), do you still hear/get air problems?

The boiler stat is set to 70C?, what is the TS stat set to?.

Are those Grundfos pumps the old Selectric type?.

Hi there, the boiler is at 70Deg, the TS thermostat is not connected yet and there is room thermostat controlling the heating set at 20Deg
With the boiler turned off only the single CH pump running, there is little air being sucked in, I would say slightly less than when run with the boiler and boiler pump on as well.
Yes the pumps are the old selectric type.

 

[iainf3]

Hi there, the boiler is at 70Deg, the TS thermostat is not connected yet and there is room thermostat controlling the heating set at 20Deg
With the boiler turned off only the single CH pump running, there is little air being sucked in, I would say slightly less than when run with the boiler and boiler pump on as well.
Yes the pumps are the old selectric type.

Hi there, the boiler is at 70Deg, the TS thermostat is not connected yet and there is room thermostat controlling the heating set at 20Deg
With the boiler turned off only the single CH pump running, there is little air being sucked in, I would say slightly less than when run with the boiler and boiler pump on as well.
Yes the pumps are the old selectric type.

Hi there, the boiler is at 70Deg, the TS thermostat is not connected yet and there is room thermostat controlling the heating set at 20Deg
With the boiler turned off only the single CH pump running, there is little air being sucked in, I would say slightly less than when run with the boiler and boiler pump on as well.
Yes the pumps are the old selectric type.

I must admit that when Ch pumps kicks in you hear air in the system especially going round the flow pipe from the boiler and as mentioned when the pumps stop the cold water in the F&E tank flow righ5 back down to the bottom of the TS. I have attached a image showing the S-bend I put on it yesterday which does seem to help in slowing down the hot water to the F&E tank.

 

[John.g]

Are you getting any air from the rads when/if you bleed them with the CH circ pump off?.
Are you sure there's no other vent somewhere on the CH system?
What are the dimensions roughly of the F&E tank?
What tells the boiler and its circ pump to start and when the burner cuts out does the circ pump keep running?
Does the burner cycle on/ off fairly rapidly?

Edit: I see the F&E tank is 20L capacity.

 

[iainf3]

Are you getting any air from the rads when/if you bleed them with the CH circ pump off?.
Are you sure there's no other vent somewhere on the CH system?
What are the dimensions roughly of the F&E tank?
What tells the boiler and its circ pump to start and when the burner cuts out does the circ pump keep running?
Does the burner cycle on/ off fairly rapidly?

Edit: I see the F&E tank is 20L capacity.

Hello, A wee bit, but did stick that S pipe on the cold feed yesterday as I have just checked it and cleared all will check tomorrow. This is the most the heating has been running have pushed it on all day to see what happens.
The tank is 430 x 300 x 300 high and sits around half full.
The only other vent is the auto air valve on the boiler flow pipe which has been I service for the last 15 years.

On DWH only the boiler and the it’s circ pump start together but once up to temperature eg 70degC the boiler stops and the circ pump continues.

On CH, when selected and the room stat is requesting heat, the boiler and its circuit start up together with the CH pump, but when the room stat reaches temperature it will stop the CH pump as well as both the boiler and its circ pump.

It the unlikely event the boiler gets to temperature first it will be as above and only stop the boiler. This was done to Honeywell heating control drawing, not and S or Y plan, no valves on the system

 

[John.g]

Are you sure that the AAV is working properly on the boiler flow pipe they have a great knack of getting blocked up, I would normally have a isol valve to facilitate cleaning them periodically.

 

[iainf3]

Are you sure that the AAV is working properly on the boiler flow pipe they have a great knack of getting blocked up, I would normally have a isol valve to facilitate cleaning them periodically.

Are you sure that the AAV is working properly on the boiler flow pipe they have a great knack of getting blocked up, I would normally have a isol valve to facilitate cleaning them periodically.

Hello, I don’t know if I am honest I haven’t really had issue before to look at it. It wouldn’t be a proble to take it off and see,
I am looking to drain the system again and change out these opposing tees on the return for the CH circuit. Basically on the main return back to the TS the main bedroom and sitting room are both 15mm returns which come into the 22mm Tees directly opposite main return flow, I am assuming this would cause restriction to the CH system although its been like that for the last 25years

 

[John.g]

If the returd is basically two rads with 15mm returns teeing into the main 22mm return then seems normal?.

 

[iainf3]

Hello, I don’t know if I am honest I haven’t really had issue before to look at it. It wouldn’t be a proble to take it off and see,
I am looking to drain the system again and change out these opposing tees on the return for the CH circuit. Basically on the main return back to the TS the main bedroom and sitting room are both 15mm returns which come into the 22mm Tees directly opposite main return flow, I am assuming this would cause restriction to the CH system although its been like that for the last 25years

Hello, from your last note, I had look at the AAV and found a new one in the garage and have stuck it onto eliminate all threats. Will try it on now and see if that helps any.

 

[John.g]

Very good and just ensure the boiler circ pump is pumping into the boiler return which no doubt you have checked anyway.

 

[iainf3]

Hello, from your last note, I had look at the AAV and found a new one in the garage and have stuck it onto eliminate all threats. Will try it on now and see if that helps any.

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

 

[iainf3]

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

Hello, Please see attached sketch of how the bedroom and sitting rad returns tee into the main return pipe, hope that explains better

Hi JohnG, did you see the sketch of the radiator connections in the previous post, does that make sense about opposing tees or is this not worth bothering about. Many thanks for the help to date

 

[John.g]

I have two rads upstairs connected exactly the same way and even have a 1.5M length of 15mm from the T to the main 22mm return pipe, these rads work fine in my 50 year old open vented system.