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

[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