Central heating pump

[John.g]

Bypass on its own shouldn't increase boiler demand,
Can you just run on DHW demand only and see what kind of cycling and flow/return temps you are getting.
Also ensure you check those manifold temperatures sometime.

 

[sherylryan]

Bypass on its own shouldn't increase boiler demand,
Can you just run on DHW demand only and see what kind of cycling and flow/return temps you are getting.
Also ensure you check those manifold temperatures sometime.

Ok, I’ll go do that now. I have turned the manifold temperatures down like you suggested yesterday. (Is that what you mean)

 

[John.g]

No, the next time the troubled manifold is on check the temperatures where highlighted with the heat gun as suggested in post 69, we can then see if that TMV is bypassing.

 

[sherylryan]

No, the next time the troubled manifold is on check the temperatures where highlighted with the heat gun as suggested in post 69, we can then see if that TMV is bypassing.

Ok, yes i wil do that. Well I ran the DHW system and this was the result

View attachment 76410
But also while I was standing there, I think I've discovered the problem. We have two pipes running from the boiler to the gas boiler as the radiators are piped to work on gas if something happens to the boiler. On further inspections these flow and return pipes are exceptionally hot, and the DHW is in the complete opposite direction. As you can see from the photos there are 2 valves but these are only shut if the rads are operating by the gas boiler. So it would seem we have flow going along these pipes circulating into the gas boiler, and heading back to the other boiler. This is a 28m loop
( I do hope that makes sense ) This would also explain why the boiler return temperature is higher than the manifold return temp.

 

[John.g]

Can you shut those valves temporarily and put a note on the gas boiler to that effect and see how the UFH operates.
Can't see attachment 76410 re DHW.

 

[sherylryan]

Can you shut those valves temporarily and put a note on the gas boiler to that effect and see how the UFH operates.
Can't see attachment 76410 re DHW.

Yes I can shut those valves temporarily, if the rads call for heat off this troubled boiler they use those pipes for flow and return, both boilers can not operate at the same time. The gas is purely for backup.
Attached DHW graph

 

[John.g]

If you mean that the boiler ran continuously for 45.37 mins then its output was ~ 19.7kwh and if all that energy was inputted to the hot water cylinder then the cylinder volume would need to be 846 liters to only rise by 20C, not likely, if the HW cylinder is say a more realistic 250 liters then it would only take 5.81kwh or 13.5 min to rise it by 20C. still not clear as to what's going on but with these valves now closed then it may be become clearer.

 

[sherylryan]

If you mean that the boiler ran continuously for 45.37 mins then its output was ~ 19.7kwh and if all that energy was inputted to the hot water cylinder then the cylinder volume would need to be 846 liters to only rise by 20C, not likely, if the HW cylinder is say a more realistic 250 liters then it would only take 5.81kwh or 13.5 min to rise it by 20C. still not clear as to what's going on but with these valves now closed then it may be become clearer.

No boiler didn’t run continuously, the blue on the graph is where the flame stops but the pump still runs to circulate the water, the boiler only fired for 29 mins 38 seconds out of the 44.37 mins (sorry was not clear on my outcome)

 

[ShaunCorbs]

There’s a set of valves on the boiler so worth a test

 

[sherylryan]

No boiler didn’t run continuously, the blue on the graph is where the flame stops but the pump still runs to circulate the water, the boiler only fired for 29 mins 38 seconds out of the 44.37 mins (sorry was not clear on my outcome)

Hi John
I run the troubled manifold with the rad valves turned off and the boiler return temp was exactly the same as the ufh manifold return temp. Although the boiler ran continuously for 42.07 mins and only got to 59 degrees. The manifold points you told me to measure were spot on, so the TMV is doing it’s job. I now believe the pump set to constant pressure and being such a big pump is another issue, as water was also bypassing through the external bypass.

As you can see the Rads literally T into the flow and return so no valves to stop the flow of water, with valves turned off water was still flow the this point in these pipes.

 

[John.g]

So install zone valve on rads and problem solved?.

 

[sherylryan]

So install zone valve on rads and problem solved?.

There are zones valves already on the rads but because of the new piping the have stuffed it up, so new pipe work and zones valves I’m picking