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

[Benny895]

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.

 

[John.g]

That would indicate that the K3 is emitting at least 5kw which I think is its rated output with flow/return temps of 75C/65C.

 

[Ben-gee]

If these are daisy chained in 15 mm pipe, that is the problem. Need to feed individually in 15mm teed from main 22mm flow/returns.

 

[John.g]

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.

 

[ShaunCorbs]

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

1.6m John 857lph at 20kw

 

[John.g]

Yes, at a dT of 20C but if a dT of 15C required then flow is 1146LPH so dP is, ~ 1.6*(1146/857)^2, 2.86M.

 

[ShaunCorbs]

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

 

[John.g]

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.

 

[ShaunCorbs]

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.

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

 

[John.g]

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.

 

[Benny895]

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

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

 

[John.g]

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.

 

[Benny895]

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

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

 

[Benny895]

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

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]

Excellent news, what mode and setting are you running the UPS3 at?

 

[Benny895]

Excellent news, what mode and setting are you running the UPS3 at?

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

 

[John.g]

Is it a sealed system with expansion vessel?

 

[Benny895]

Is it a sealed system with expansion vessel?

Hello John

My system is an open vented system with a loft tank. Some of the methods I used to clear the air locks earlier on in my posts would not work with combo systems or pressurised systems and could damage the system.

Ben

 

[John.g]

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.

 

[Benny895]

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.

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

 

[John.g]

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.

 

[Benny895]

Hello,

Winter has come and finally I have a warm house with the K3 and the two smaller width K2s heating the whole house. Collectively the three rads I changed went from 4000-5000 BTU approx. To 30,150 BTU. The 1.8metre by 700mm height K3 is a beast and heats a massive space and thereby the whole house.

Would recommend K3 for cold houses or large cold spaces.

Thank you for all contributors helping with some issues faced.

Ben