Central heating pump

John.g · Jul 2, 2022

The above makes no real sense either as the temperature keeps rising when the burner is apparently off.

What signal/indication are you using to tell you that the burner is firing or not?.

I would suggest monitoring the burner firing time (boiler on/off) by watching the flame actually coming on/off in the viewing window and monitoring the temperatures.
I would also suggest that you do the above on the UFH(s) and monitor the manifold flow temp (which I don't think you have been) and note the total flow as per the flow tubes, the UFH output can then be cross checked reasonably well by using the % boiler cycle firing time. The manifold temperature gauges should also give reasonably accurate temperatures.

John.g · Jul 2, 2022

Is this manifold plumbed correctly?.

sherylryan · Jul 3, 2022

John.g said:
The above makes no real sense either as the temperature keeps rising when the burner is apparently off.

What signal/indication are you using to tell you that the burner is firing or not?.

I would suggest monitoring the burner firing time (boiler on/off) by watching the flame actually coming on/off in the viewing window and monitoring the temperatures.
I would also suggest that you do the above on the UFH(s) and monitor the manifold flow temp (which I don't think you have been) and note the total flow as per the flow tubes, the UFH output can then be cross checked reasonably well by using the % boiler cycle firing time. The manifold temperature gauges should also give reasonably accurate temperatures.

I monitored the boiler exactly how you suggest. I will do the manifold today, it’s very confusing as to why the temp rises when the flame is off.

John.g · Jul 3, 2022

It sure is, and the other puzzle is that Laundry manifold (the good one?) above which seems to be sending mixed water temperature back to the boiler, also the pump is connected between the UFH cold return and the manifold flow, the troubled manifold is plumbed the normal way like below.

sherylryan · Jul 3, 2022

John.g said:
It sure is, and the other puzzle is that Laundry manifold (the good one?) above which seems to be sending mixed water temperature back to the boiler, also the pump is connected between the UFH cold return and the manifold flow, the troubled manifold is plumbed the normal way like below.
View attachment 76356

The troubled manifold was plumbed the same as the laundry manifold until 4 weeks ago, we changed the pump set. We are going to replace the laundry pump set the the same as above as well.

John.g · Jul 3, 2022

Just check also that the flow through the boiler is in tht right direction.

sherylryan · Jul 3, 2022

John.g said:
Just check also that the flow through the boiler is in tht right direction.

Ok I’ll have a look, thank you

sherylryan · Jul 3, 2022

sherylryan said:
Ok I’ll have a look, thank you

Well I have watched the flow and return on the manifold after the mixing valve which was set to 42 degrees, I found the flow going into the manifold reached 52 degrees. The boiler fired continuously for the entire 2 hours and 25 minutes. As far as the flow rates through the circuits were 5 @ 3lpm, 3 @ 4lpm, 1@ 2.5lpm, a total of 29.5lpm. As per attached photos the flow meters were turned down low but still showing extreme flow through them. (Sorry about the sideway photos)

Screen Shot 2022-07-03 at 7.52.46 PM.png

John.g · Jul 3, 2022

Very good, all adds up thermodynamically any way, S.sheet shows boiler output of 24.7kw, almost flat out, hence constant firing.
Suggest throttling hot water before the manifold to see if mixing temp drops, this would then point to excesss boiler feed pump pressure and/or reduce manifold pump to speed 2, at least that will point you, hopefully, in the right direction.

sherylryan · Jul 3, 2022

So the o

John.g said:
Very good, all adds up thermodynamically any way, S.sheet shows boiler output of 24.7kw, almost flat out, hence constant firing.
Suggest throttling hot water before the manifold to see if mixing temp drops, this would then point to excesss boiler feed pump pressure and/or reduce manifold pump to speed 2, at least that will point you, hopefully, in the right direction.

View attachment 76367

Thanks John you are very helpful. So our boiler originally 35kw was fine and didn’t need to be downsized at all. If it’s firing ar 24.7 kw with the Troubled manifold it clearly isn’t going to run the 2 x UFH manifold/circuits, 15 radiators and 28m of trench, in fact I wonder when all of them are firing 35 kw was also to small as well.

John.g · Jul 3, 2022

Yes but remember you don't have any control
Over the heat output of the UFH since you have no control of the mixing temperature, this will have to be sorted out.

sherylryan · Jul 3, 2022

John.g said:
Yes but remember you don't have any control
Over the heat output of the UFH since you have no control of the mixing temperature, this will have to be sorted out.

The pump set is only 3 weeks old are you suggesting the mixing valve could be faulty? Hence the water entering the manifold at a temperature higher than the set value?

John.g · Jul 3, 2022

Possibly but unlikely, the boiler circ pump pressure though at 1.4bar or whatever may be preventing it from operating correctly which is why I suggested throttling it somewhere. Most boiler circ pumps will only be running with a head of 4M (0.4bar) or so. I throttling it works, re install your old pump.

sherylryan · Jul 3, 2022

John.g said:
Possibly but unlikely, the boiler circ pump pressure though at 1.4bar or whatever may be preventing it from operating correctly which is why I suggested throttling it somewhere. Most boiler circ pumps will only be running with a head of 4M (0.4bar) or so. I throttling it works, re install your old pump.

Yes I agree re installing old pump, I will try throttling the pump back again and also turn the manifold pump back to 2, it’s currently set on 3. I must admit the floors are heating up better with the new pump set as opposed to the pump set on the good manifold. John thank you very much for all the information you have supplied to me. To balance a ufh manifold is it only done with the flow meters, or can you slow the return water?

John.g · Jul 4, 2022

John.g said:
Possibly but unlikely, the boiler circ pump pressure though at 1.4bar or whatever may be preventing it from operating correctly which is why I suggested throttling it somewhere. Most boiler circ pumps will only be running with a head of 4M (0.4bar) or so. I throttling it works, re install your old pump.

I wouldn't reduce the flow rate excessively as the loops are parallel circuits and you want to keep the flows equal, temperature control is the way go INO.

temperature reduction/control is the way to go O

sherylryan · Jul 4, 2022

John.g said:
I wouldn't reduce the flow rate excessively as the loops are parallel circuits and you want to keep the flows equal, temperature control is the way go INO.

temperature reduction/control is the way to go O

Hi John, well I have throttled back the boiler pump to 1 bar and the manifold pump to speed setting 2 and I achieved 65 degrees flow, and 49 degrees return at the boiler and 45 degree flow through the manifold and 35 return. The boiler is cycling though of 15 mins on 1.15 mins off. I feel we are getting somewhere 🙂

John.g · Jul 5, 2022

Numbers not adding up there as the boiler return temp should be the same as the manifold return temp at 35C (assuming UFH only on)

sherylryan · Jul 5, 2022

John.g said:
Numbers not adding up there as the boiler return temp should be the same as the manifold return temp at 35C (assuming UFH only on)

View attachment 76398

Hi John I thought that as well, yes underfloor only on, once the manifold was up to temp would the excess water return back to boiler, making the boiler return higher? I did notice however that with the boiler thermostat set to 60, the flow did get as high as 70 at one point. I see there are two ports on either side on the top of the boiler ther thermostat probes are in the left, I am picking that has actually been set up correctly.

John.g · Jul 5, 2022

Maybe this TMV is sending mixed flow temperature water back to the boiler?, I always thought it was supposed to be the UFH cold water return.
The boiler thermostat should control the flow temperature at whatever setpoint its set to.
Did you check that the boiler flow and return pipes are installed correctly?.

sherylryan · Jul 5, 2022

John.g said:
Maybe this TMV is sending mixed flow temperature water back to the boiler?, I always thought it was supposed to be the UFH cold water return.
The boiler thermostat should control the flow temperature at whatever setpoint its set to.
Did you check that the boiler flow and return pipes are installed correctly?.

interesting you say that because yesterday the laundry manifold had a flow of 60 at the boiler and returning 59, and that water has to travel 55m there and back.
I checked the flow and return out of the boiler, and the seem to be ok.
Another thought I’ve just had, I think this boiler is way undersized even at the original 35kw. This diesel boiler replaced a 26kw gas boiler which ran all the rads and trench heating and replaced a 16 kw heat pump that was to small to run the underfloor heating, hence why we decided to change. Is there a formula to work out what size boiler one would need.

We already know that when the troubled manifold is on it needs 24.7kw.

ShaunCorbs · Jul 5, 2022

sherylryan said:
interesting you say that because yesterday the laundry manifold had a flow of 60 at the boiler and returning 59, and that water has to travel 55m there and back.
I checked the flow and return out of the boiler, and the seem to be ok.
Another thought I’ve just had, I think this boiler is way undersized even at the original 35kw. This diesel boiler replaced a 26kw gas boiler which ran all the rads and trench heating and replaced a 16 kw heat pump that was to small to run the underfloor heating, hence why we decided to change. Is there a formula to work out what size boiler one would need.

We already know that when the troubled manifold is on it needs 24.7kw.

What’s the flow rate of all the zones on this manifold ?

sherylryan · Jul 5, 2022

ShaunCorbs said:
What’s the flow rate of all the zones on this manifold ?

Out of the 7 zones, only 4 are operating as the other zones are turned off. 2 x 2.4LPM, 1 x 2.0LPM and 1x 1.5LPM (small laundry circuit) so approx 8.3 lpm in total. This manifold is 55 m away from the boiler.

ShaunCorbs · Jul 5, 2022

Which is 4kw required so very strange why it needs 5 x that

John.g · Jul 6, 2022

sherylryan said:
interesting you say that because yesterday the laundry manifold had a flow of 60 at the boiler and returning 59, and that water has to travel 55m there and back.
I checked the flow and return out of the boiler, and the seem to be ok.
Another thought I’ve just had, I think this boiler is way undersized even at the original 35kw. This diesel boiler replaced a 26kw gas boiler which ran all the rads and trench heating and replaced a 16 kw heat pump that was to small to run the underfloor heating, hence why we decided to change. Is there a formula to work out what size boiler one would need.

We already know that when the troubled manifold is on it needs 24.7kw.

Something definitely very strange, I get a UFH heat output of 5.8kw at your flowrate of 8.3LPM and dT of 10C which should only result in a boiler flowrate of 2.77LPM at a boiler return temp of 35C., the measured return is 49C which means that 2.42LPM at 65C is either bypassing through the TMV or through a external bypass to give a boiler return flow of 5.2LPM. But the boiler is outputting ~ 24kw based on your burner cycling times, you may be losing up to 5kw in all that pipework if uninsulated but still wouldn't remotely account for that boiler output, the only logical explanation is that there is another zone (maybe rads) on as well, taking the few temperatures I suggested will show if the TMV is by passing but will not explain the very high boiler output.

sherylryan · Jul 6, 2022

ShaunCorbs said:
Which is 4kw required so very strange why it needs 5 x that

John.g said:
Something definitely very strange, I get a UFH heat output of 5.8kw at your flowrate of 8.3LPM and dT of 10C which should only result in a boiler flowrate of 2.77LPM at a boiler return temp of 35C., the measured return is 49C which means that 2.42LPM at 65C is either bypassing through the TMV or through a external bypass to give a boiler return flow of 5.2LPM. But the boiler is outputting ~ 24kw based on your burner cycling times, you may be losing up to 5kw in all that pipework if uninsulated but still wouldn't remotely account for that boiler output, the only logical explanation is that there is another zone (maybe rads) on as well, taking the few temperatures I suggested will show if the TMV is by passing but will not explain the very high boiler output.

I’m with you John it is very strange. All pipe work is insulated, we have doubled checked the flow and return today and all seems ok. There is an external bypass on the boiler but nothing seems to be flowing through it, as the pipes are cold. I wonder if it because of the stupid pump setup on the laundry manifold it’s bypassing and going back to the boiler. I’m about ready to rip the whole system out 😂😂😂 I really can’t find an answer.

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