Just fitted K3 radaitor and the centre front panel won’t heat up

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Benny895

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I have started fitting new radiators in my house. The lounge kitchen gets very cold in the winter and is a big room that has previously had an extension put on it and is 19.5 metres by 6.5 metres with a 2.25metre high ceiling.

I started by replacing an old radaitor with a 1200x 600mm K2. Which heats up and works fine, great heat by Stelrad. I have this weekend fitted a K3 1800x700mm. I have this Radaitor hot but the lower centre front panels I can’t get hot. It does feel like the lower half of the radaitor (especially the front panel as that’s what I can get my hand too) isn’t burning hot like the K2. I have tried almost everything apart from actual changing components; I have bled the rads, shut the system down to one rad, balanced the system, the central heating pump is on max.

This Radaitor is working and convecting but not as hot as it should be.


Grundfos UPS 2-50/60
System / non Combi
4rads upstairs 2 hand towel rails
7 rads downstairs one towel rails
25kw boiler

Has anyone else experience this with k3 / triple panel Radaitors. Not a lot of posts online about triple panel radaitors. Some more posts and specifics about K3 issues would be helpful.
 
Have you tried turning all the other ones off to see if it heats up Fully ?
 
Maybe worth draing down and refilling very slowly with vent plugs/blanks at both ends removed. A K31800X700 stelrad has a output of 4.88kw and will require a flowrate of 7LPM at 75C/65C/20C, (50 deg rad).
 
ChrisB1982 said:
Does the radiator have baffles inside and has it been fitted correctly? What size is your pipework?
Click to expand...
The pipe work is 15mm coming out the floor. I have not fitted baffles. Concerning the baffles the heat is going up and around back to the return but then not dropping down the panels easily. The front panel has the most cool areas in the bottom half and centre I think (could potentially support a baffle to flow to the front panel). The back panel at the bottom is hot and gets slightly cooler at the bottom towards the centre. If I turn on the rest of the system thinking it is getting slightly cooler after balancing.

I am not a plumber but someone who does diy I have fitted it the same as the K2 so i think it is fitted correctly.

I think I might be in the limits of the central heating pump. The radaitor is probably the furthest from the heat source as it is in the extension. I think the pump does 3m cubed an hour.

What do you guys think the whole Radaitor does not heat properly when sectioned of for the system just to heat one radaitor. If there was a baffle it would need to be fitted near the plug at the top the opposite end to the bleed valve to point flow towards the front panel?

The flow pipe is hot the exit pipe is warm.

Thank you for any suggestions.
 
It’s not the pump as you’ve shut all the other radiators and it still doesn’t heat up what brand of k3 is it ?
 
Benny895 said:
Hello Shaun, it’s a stelrad K3 compact I ordered it online from their website. The packaging said K3 compact Vita.
Click to expand...

Might be worth contacting them to see if there’s anything wrong / needs a baffle etc
 
Looks like a circulation problem as the return is only warm, if the water was short circuiting then the return would be very hot, surprising the return isnt hot even with all the other rads shut off, even if it was circulating 7LPM then the 15mm tails should be OK except that they are exceptionally long. I think there may be air trapped in there somewhere interfering with the flowrate except a lockshield throttled or its been inadvertently piped up as a one pipe system.
 
Benny895 said:
Yes the lock shield is fully open. I have fully opened both valves. I will contact stelrad to see if there is anything they can suggest. Any other ideas I am all ears.
Click to expand...

Try closing it half way (the lockshield)
 
I think L/S valves have a valve co efficient of 1 so 2 might require a dP of ~ 3.5M at a flowrate of 7LPM ().42m3/hr). A UPS 2 will give a head of 6M at this flowrate so there certainly should be no problem in driving the water through that rad especially with all other rads isolated but the return temperature should only be 4 or 5C lower than the flow temperature, this wasn't happening, the only conceivable reason for this from a pump point of view is that the pump is not running in full speed mode 3 but is on one of the proportional pressure modes which are hopeless on this pump, PP3 will only give a flow of 0.42m3/hr at a 1.6M head but this should have shown up before changing out the rad?.
 
John.g said:
Looks like a circulation problem as the return is only warm, if the water was short circuiting then the return would be very hot, surprising the return isnt hot even with all the other rads shut off, even if it was circulating 7LPM then the 15mm tails should be OK except that they are exceptionally long. I think there may be air trapped in there somewhere interfering with the flowrate except a lockshield throttled or its been inadvertently piped up as a one pipe system.
Click to expand...

Thanks John next weekend. I will try to purge the Radaitor and system of any air. I will attach a hose to the Radaitor bleed valve and then open the shut TRV valve
John.g said:
I think L/S valves have a valve co efficient of 1 so 2 might require a dP of ~ 3.5M at a flowrate of 7LPM ().42m3/hr). A UPS 2 will give a head of 6M at this flowrate so there certainly should be no problem in driving the water through that rad especially with all other rads isolated but the return temperature should only be 4 or 5C lower than the flow temperature, this wasn't happening, the only conceivable reason for this from a pump point of view is that the pump is not running in full speed mode 3 but is on one of the proportional pressure modes which are hopeless on this pump, PP3 will only give a flow of 0.42m3/hr at a 1.6M head but this should have shown up before changing out the rad?.
Click to expand...

I have checked the pump and it is working on max power. Tried turning it down and it didn’t do anything obviously. Thanks for confirming
 
John.g said:
Looks like a circulation problem as the return is only warm, if the water was short circuiting then the return would be very hot, surprising the return isnt hot even with all the other rads shut off, even if it was circulating 7LPM then the 15mm tails should be OK except that they are exceptionally long. I think there may be air trapped in there somewhere interfering with the flowrate except a lockshield throttled or its been inadvertently piped up as a one pipe system.
Click to expand...

Hello John
I tried letting some water and air out of the system to clear any airlock. I let some air and water out the front door with a hose pipe. No joy on that front.

On another note we do have 5 cast iron old double panel non convector radaitors on the system. Could this cause any issues? Was thinking about replacing them anyway for smaller height modern radaitiors.

But still don’t get why the K3 won’t heat up when the system is shut down to one radaitor.

Kind regards

Ben
 
How long have you left it on as the only radiator for?

Whats your bypass set to?

Have you shut the motorised valve to the cylinder? If it's a Y plan have you turned the cylinder stat down to close the valve?

Are you on an open vented system or sealed?

Sounds like Air or pipe restriction/damaged. What size was the old rad?

If its air you can shut the TRV/lockshield off, open the air vent and wet vac or towel the water that comes out. Remove the air vent and connect a hose to it using a spare rad valve and some ptfe. Now open one end of the radiator one at a time full bore and run the hose to a bucket or drain, if you hear gurgling that's good news if not then its unlikely to be air.

If its a blockage try removing the rad, fitting a hose to each rad valve then a pressure testing pump as far back on the pipework as you can without going past a tee. pump it up until you're getting a nice flow out the end of the hose then repeat the other side.
 
Last edited:
John.g said:
I think L/S valves have a valve co efficient of 1 so 2 might require a dP of ~ 3.5M at a flowrate of 7LPM ().42m3/hr). A UPS 2 will give a head of 6M at this flowrate so there certainly should be no problem in driving the water through that rad especially with all other rads isolated but the return temperature should only be 4 or 5C lower than the flow temperature, this wasn't happening, the only conceivable reason for this from a pump point of view is that the pump is not running in full speed mode 3 but is on one of the proportional pressure modes which are hopeless on this pump, PP3 will only give a flow of 0.42m3/hr at a 1.6M head but this should have shown up before changing out the rad?.
Click to expand...

I did just check the pump and is it on constant highest setting. The old rad did not have these problems I don’t think. It had Radaitor cover on it so I can’t be 100%.
 

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Would say lack of flow through the rad is the issue
 
If the TRV isn't new maybe replace with new one or, temporarily, just fit another L/S valve to rule out any obstruction.
Also, even though indications are that the pump is performing OK based on the K2 rads heating up, would suggest purchasing a plug in energy monitor (~£15), stick a 3 pin plug on the end of the pump cable, plug it into a extension lead and monitor the power, this will give a very accurate measurement of the pump power from which the exact flowrate can be derived from the pump curves.

Is the 25kw boiler oil or gas and what make/model?.
 

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fowlerboi said:
How long have you left it on as the only radiator for?

Whats your bypass set to?

Have you shut the motorised valve to the cylinder? If it's a Y plan have you turned the cylinder stat down to close the valve?

Are you on an open vented system or sealed?

Sounds like Air or pipe restriction/damaged. What size was the old rad?

If its air you can shut the TRV/lockshield off, open the air vent and wet vac or towel the water that comes out. Remove the air vent and connect a hose to it using a spare rad valve and some ptfe. Now open one end of the radiator one at a time full bore and run the hose to a bucket or drain, if you hear gurgling that's good news if not then its unlikely to be air.

If its a blockage try removing the rad, fitting a hose to each rad valve then a pressure testing pump as far back on the pipework as you can without going past a tee. pump it up until you're getting a nice flow out the end of the hose then repeat the other side.
Click to expand...
John.g said:
If the TRV isn't new maybe replace with new one or, temporarily, just fit another L/S valve to rule out any obstruction.
Also, even though indications are that the pump is performing OK based on the K2 rads heating up, would suggest purchasing a plug in energy monitor (~£15), stick a 3 pin plug on the end of the pump cable, plug it into a extension lead and monitor the power, this will give a very accurate measurement of the pump power from which the exact flowrate can be derived from the pump curves.

Is the 25kw boiler oil or gas and what make/model?.
Click to expand...
The boiler is an alpha 24r. I have been working on having another go at any airlocks in the system tonight as I work in the day. Heating system on and drainage out the front door
John.g said:
If the TRV isn't new maybe replace with new one or, temporarily, just fit another L/S valve to rule out any obstruction.
Also, even though indications are that the pump is performing OK based on the K2 rads heating up, would suggest purchasing a plug in energy monitor (~£15), stick a 3 pin plug on the end of the pump cable, plug it into a extension lead and monitor the power, this will give a very accurate measurement of the pump power from which the exact flowrate can be derived from the pump curves.

Is the 25kw boiler oil or gas and what make/model?.
Click to expand...
The boiler is alpha 24r.

I have done some more testing and airlock freeing over the last couple of days. I have managed to clear the airlocks I think. I drained the water of the drain away Radaitor (and out the front door) and ran the heating system at the same time.Also when shutting down to the one radaitor.

The result is shut down all the radaitors and four down stairs radaitors open (3 of them the cast iron former lounge Radaitors) The Radaitor heats to a satisfactory standard. Both the in flow and outflow pipes are hot of the K3. Once I attempt to balance the system the K3 half heats.

What I’m thinking and I am going to do anyway because the house needs it; is the following. But this is a summer project. So won’t be immediate. In the former lounge it has three old cast iron double panel Radaitors, these can struggle to heat along with the K3 in similar manner (often only one struggling to heat) This room I’m going to change to one rad and get just as much heat but a type 22. Then get the other two removed and pipework tapped off. The hallway I have a cast iron rad which again I’m going to change (this is the drain away rad) to a type 22. Then I have two different bedrooms with cast iron rads. These I’m going to change for modern Radaitors one probably a type 22 and the other needs a single panel with fins.

This should create enough flow through the system by making it more efficient removing 2 rads and swapping the others for more efficient rads and probably slightly smaller as I’m swapping from imperial. I’m on 14 rads and 3 towel rails. My system should power 10-15 rads. Removing the (very old) cast iron (all) double panel rads and replacing them should make a difference.

What are your thoughts? Really interested of any opinions.
 
Is it all off one 15mm drop or each on there own drop of 15mm off a 22mm
 
Benny895 said:
The boiler is an alpha 24r. I have been working on having another go at any airlocks in the system tonight as I work in the day. Heating system on and drainage out the front door

The boiler is alpha 24r.

I have done some more testing and airlock freeing over the last couple of days. I have managed to clear the airlocks I think. I drained the water of the drain away Radaitor (and out the front door) and ran the heating system at the same time.Also when shutting down to the one radaitor.

The result is shut down all the radaitors and four down stairs radaitors open (3 of them the cast iron former lounge Radaitors) The Radaitor heats to a satisfactory standard. Both the in flow and outflow pipes are hot of the K3. Once I attempt to balance the system the K3 half heats.

What I’m thinking and I am going to do anyway because the house needs it; is the following. But this is a summer project. So won’t be immediate. In the former lounge it has three old cast iron double panel Radaitors, these can struggle to heat along with the K3 in similar manner (often only one struggling to heat) This room I’m going to change to one rad and get just as much heat but a type 22. Then get the other two removed and pipework tapped off. The hallway I have a cast iron rad which again I’m going to change (this is the drain away rad) to a type 22. Then I have two different bedrooms with cast iron rads. These I’m going to change for modern Radaitors one probably a type 22 and the other needs a single panel with fins.

This should create enough flow through the system by making it more efficient removing 2 rads and swapping the others for more efficient rads and probably slightly smaller as I’m swapping from imperial. I’m on 14 rads and 3 towel rails. My system should power 10-15 rads. Removing the (very old) cast iron (all) double panel rads and replacing them should make a difference.

What are your thoughts? Really interested of any opinions.
Click to expand...
I should mention the 14 rads in total include 3 towel rails as rads
 
I had thought you had said that the K3s return temperature was only lukw warm even when on its own, the minimum output of your boiler is 6.5kw, if/when you run the K3 on its own does the boiler cycle on/off fairly rapidly, and same for other 3 in the former lounge if you just run those together.
 
John.g said:
I had thought you had said that the K3s return temperature was only lukw warm even when on its own, the minimum output of your boiler is 6.5kw, if/when you run the K3 on its own does the boiler cycle on/off fairly rapidly, and same for other 3 in the former lounge if you just run those together.
Click to expand...
When I just run the K3; the boiler stays on all the time. When running the boiler with the K3 and the 3 in the former lounge then it also doesn’t cycle and just stays in all the time. I haven’t ran the 3 in the lounge by themselves.

Initially when I ran the K3 by itself and the outflow to the K3 pipe was Luke warm, the boiler would cycle off and then back on.
 
There's also a fairly high pressure drop through even the clean boiler Hx, if you wanted say 20kw output at a dT of 15C, (1146LPH) (to achieve reasonably high radiator outputs then the Hx pressure drop alone is almost 3M so doesn't leave much remaining head available to circulate the system if a LLH isn't installed.

1683796067873.png
 
John.g said:
There's also a fairly high pressure drop through even the clean boiler Hx, if you wanted say 20kw output at a dT of 15C, (1146LPH) (to achieve reasonably high radiator outputs then the Hx pressure drop alone is almost 3M so doesn't leave much remaining head available to circulate the system if a LLH isn't installed.

View attachment 83378
Click to expand...

1.6m John 857lph at 20kw
 
But boiler will want dt20 and will cycle to demand that system may be designed at dt15 but boiler will regulate itself at dt20 by cycling
 
I thought the 20C dT was a sort of standard to compare different boilers but didn't know that the boiler would try and maintain this but difficult on a heat only boiler since it doesnt contol the circ pump. Some Vaillants have return temperature control but I rarely see it mentioned.
 
John.g said:
I thought the 20C dT was a sort of standard to compare different boilers but didn't know that the boiler would try and maintain this but difficult on a heat only boiler since it doesnt contol the circ pump. Some Vaillants have return temperature control but I rarely see it mentioned.
Click to expand...

Yes vaillants and gloworms are the worst for it viessmann also cycle a bit if dt is low

It’s more down to pcb logic and estimates it’s take x to heat from this to this so flow rate is y etc
 
This shows perhaps why a K3's front panel doesn't heat up as much as the others and should also be filled very slowly?.
I have quite a few old double panel type 22s, these have only two little manifolds on the bottom connecting the two panels, nothing on the top except two bracing strips of welded on steel plate but both panels have separate air vents which makes them very easy to refill and get rid of the air.

1683844716197.png
 
John.g said:
This shows perhaps why a K3's front panel doesn't heat up as much as the others and should also be filled very slowly?.
I have quite a few old double panel type 22s, these have only two little manifolds on the bottom connecting the two panels, nothing on the top except two bracing strips of welded on steel plate but both panels have separate air vents which makes them very easy to refill and get rid of the air.

View attachment 83388
Click to expand...
Hello John,
I have been sick and holiday so very distracted and haven’t got back to my thread.
But yes I do agree, I think at least with large Radaitors a heating system with excellent circulation/ pressure or at least where the K3 is fitted (such as upstairs next to the boiler). Would really help the front panel heat up, but yes the front panel does tend to be diverted around slightly.

Ben
 
Glad to hear, Ben, that you are back in form again,

Regarding that pesky K3, Renewing the cast iron rads should help but I feel that installing a UPS3 pump would improve the flow considerably as you have established that the rad does, more or less, emit its rated output when running on its own since the boiler doesn't cycle on/off.
The UPS3 is a giant of a pump even though a "6M"(6.4) pump like the UPS2, (6.2M) see below.
The other alternative is to install a low loss header, LLH, where one pump deals with the boiler heat exchanger pressure loss and the other pump deals with the rads/system losses.

1685730229372.png



1685730015027.png
 
John.g said:
Glad to hear, Ben, that you are back in form again,

Regarding that pesky K3, Renewing the cast iron rads should help but I feel that installing a UPS3 pump would improve the flow considerably as you have established that the rad does, more or less, emit its rated output when running on its own since the boiler doesn't cycle on/off.
The UPS3 is a giant of a pump even though a "6M"(6.4) pump like the UPS2, (6.2M) see below.
The other alternative is to install a low loss header, LLH, where one pump deals with the boiler heat exchanger pressure loss and the other pump deals with the rads/system losses.

View attachment 83652


View attachment 83651
Click to expand...
Hello John

Thank you, the long run on the K3 I think is contributing. It has the longest run in the house. There’s at least a 4 and half metre run just in the room before it even gets out of the lounge/extension. I think the UPS3 pump will help and I will fit this over the summer when I change the Radaitors. Thank you for the technical details I was earlier considering a bigger pump but this more advance pump looks an easier option. I was looking at this link which while slightly off topic explains Pressure drops and flow rates – John Cantor Heat Pumps - https://heatpumps.co.uk/technical/pressure-drops-flow-rates/

Thank you for everyone’s help!

Ben
 
John.g said:
Glad to hear, Ben, that you are back in form again,

Regarding that pesky K3, Renewing the cast iron rads should help but I feel that installing a UPS3 pump would improve the flow considerably as you have established that the rad does, more or less, emit its rated output when running on its own since the boiler doesn't cycle on/off.
The UPS3 is a giant of a pump even though a "6M"(6.4) pump like the UPS2, (6.2M) see below.
The other alternative is to install a low loss header, LLH, where one pump deals with the boiler heat exchanger pressure loss and the other pump deals with the rads/system losses.

View attachment 83652


View attachment 83651
Click to expand...
Hello John,

This weekend I done some of the work as planned. Fitted a radiator in the downstairs hallway from a cast iron double panel to a type 22 and changed the central heating pump to the UPS 3. The K3 now heats up properly and think the downstairs lounge kitchen diner now will be warm this winter. So problems solved I think.

Ben
 
John.g said:
Excellent news, what mode and setting are you running the UPS3 at?
Click to expand...
Hello John
I tried 2 constant to start with but it didn’t rid the air from the system. Changed it to 3 constant and it heats the K3 (slowly, which I have been told is normal). The old pump ups2 15 50/60 was on 3 constant and failed to heat all the Radaitors. So 3 constant is what I would expect for the UPS 3.

Ben
 
The UPS3 is now probably pumping at it full 6.4M head (speed 3) so next time its running have a look, or get someone to have a look in the attic, and hold a "glass" of water under the vent pipe with the end of the pipe immersed in the glass and see does the level remain the same, you don't want any air ingress through the vent, also, if possible watch the vent when someone stops/starts the pump and see if any spurt of water.
 
John.g said:
The UPS3 is now probably pumping at it full 6.4M head (speed 3) so next time its running have a look, or get someone to have a look in the attic, and hold a "glass" of water under the vent pipe with the end of the pipe immersed in the glass and see does the level remain the same, you don't want any air ingress through the vent, also, if possible watch the vent when someone stops/starts the pump and see if any spurt of water.
Click to expand...
Hello John

I can check this in the near future. But I assume this won’t cause any flooding issues from the loft tank if it is to higher head? I can’t hear any air in the system and the pump is running quiet, indicating no air in the system.

Ben
 
No, wouldn't cause any flooding but you don't need any air ingress as it leads to decreased rad output, corrosion and sludge build up.
 
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