Boiler Flow / Return Temperatures

[Andy B 23]

In a bid to get my system to operate to the best of it's capabilities I have been doing some research on boiler flow/return temperatures & balancing, based on what I have discovered I have made some tweaks to my system, my home set up is as follows:

3 Bed detached house constructed in 2011, 50mm slab insulation boards in the cavity (traditional masonry internal & external skin walls).

Potterton 12 SL Promax heat only boiler, it is the original boiler, it is in good order & was serviced in Dec 23, we are now fortunate enough to live in South Devon so the climate is milder, the boiler does not work as hard as our previous boilers did in Yorkshire, temps of minus 5 to minus 10, December 2010 I recorded minus 15.

Being a modern insulated property the radiators are on the small side, the exposed pipework to the rads is 10mm copper, 22mm copper can be seen in the airing cupboard for the flow & return etc. 12 Rads in total, 10 type 11's & 2 type 21's (single convector) 10 of rads have Myson TRVs.

Grundfos Alpha 2 pump with auto adapt function.

Hive 2 thermostat.

Since moving into the house the system noise seemed a little excessive, I decided to research the pump & people were saying that after installing the same pump as mine they could hardly hear it running, I began to think that my pump had an issue so I checked on Google & then headed for the airing cupboard...

The pump speed was set to 3, after going through the various options I settled on fixed speed 2, the noise levels dropped considerably, the electric consumption also dropped from 45 watts to 20 watts.

Whilst researching the pump I came across discussions regarding flow & balancing, I discovered my flow/return temp to be very close, this did improve when I changed the pump speed.

My boiler has limited options in terms of adjustment, I have tweaked the flow temperature & now when fully warmed up the flow temp from the boiler is 75 degrees & the return is 63, I obviously need to keep the flow temperature at a suitable level to heat the water in the tank, I did get it lower but you then sacrifice the heat to the rads & HW tank. I realise that this type of boiler although manufactured to condense will not be able to do so when fully warmed up due to the higher temperatures required to heat the water.

Never attempted to balance radiators before, after several days of trial & error I have got it as best I can, previously the rad temperatures were all over the place, each one is now giving off a more uniformed temperature of around 71 degrees at the top centre of the rad, the wife even commented on the rads feeling warmer!!

Hard to obtain the 12 degree difference across the valves with the size of some of the radiators, but the rads are now all warming up at about the same rate & the heat output is definitely better.

Any thoughts on my tweaks, particularly interested in opinions about pump speeds & flow/return temps, any suggestions on how I can make any further changes?

Thanks in advance.

 

[MNW67]

I think this might be the chart for your version of this pump. The newer version seems to use fewer watts (max 35W). @Johntheo5 will be able to explain it better than I can. It might be interesting to switch to Proportional Pressure 2 (PP2) briefly, just to see how many watts that gives. Ignore the lowest blue curve, that is some sort of low power night time setback setting.

 

[Mottie]

Any thoughts on my tweaks, particularly interested in opinions about pump speeds & flow/return temps, any suggestions on how I can make any further changes?

I have my pump on the minimum speed. My theory is that it allows more time for the heat to be passed by the rads before returning to the boiler, giving a lower return temperature and hopefully more condensing. It’s just my theory though so it could be total rubbish!

 

[DP]

Andy! For condensing boiler the difference is 20 degrees. For old cast iron it was 11 degrees.

You could reduce pump speed further and see what happens.
Are you balancing the system with cylinder also calling?

 

[Johntheo5]

In a bid to get my system to operate to the best of it's capabilities I have been doing some research on boiler flow/return temperatures & balancing, based on what I have discovered I have made some tweaks to my system, my home set up is as follows:

3 Bed detached house constructed in 2011, 50mm slab insulation boards in the cavity (traditional masonry internal & external skin walls).

Potterton 12 SL Promax heat only boiler, it is the original boiler, it is in good order & was serviced in Dec 23, we are now fortunate enough to live in South Devon so the climate is milder, the boiler does not work as hard as our previous boilers did in Yorkshire, temps of minus 5 to minus 10, December 2010 I recorded minus 15.

Being a modern insulated property the radiators are on the small side, the exposed pipework to the rads is 10mm copper, 22mm copper can be seen in the airing cupboard for the flow & return etc. 12 Rads in total, 10 type 11's & 2 type 21's (single convector) 10 of rads have Myson TRVs.

Grundfos Alpha 2 pump with auto adapt function.

Hive 2 thermostat.

Since moving into the house the system noise seemed a little excessive, I decided to research the pump & people were saying that after installing the same pump as mine they could hardly hear it running, I began to think that my pump had an issue so I checked on Google & then headed for the airing cupboard...

The pump speed was set to 3, after going through the various options I settled on fixed speed 2, the noise levels dropped considerably, the electric consumption also dropped from 45 watts to 20 watts.

Whilst researching the pump I came across discussions regarding flow & balancing, I discovered my flow/return temp to be very close, this did improve when I changed the pump speed.

My boiler has limited options in terms of adjustment, I have tweaked the flow temperature & now when fully warmed up the flow temp from the boiler is 75 degrees & the return is 63, I obviously need to keep the flow temperature at a suitable level to heat the water in the tank, I did get it lower but you then sacrifice the heat to the rads & HW tank. I realise that this type of boiler although manufactured to condense will not be able to do so when fully warmed up due to the higher temperatures required to heat the water.

Never attempted to balance radiators before, after several days of trial & error I have got it as best I can, previously the rad temperatures were all over the place, each one is now giving off a more uniformed temperature of around 71 degrees at the top centre of the rad, the wife even commented on the rads feeling warmer!!

Hard to obtain the 12 degree difference across the valves with the size of some of the radiators, but the rads are now all warming up at about the same rate & the heat output is definitely better.

Any thoughts on my tweaks, particularly interested in opinions about pump speeds & flow/return temps, any suggestions on how I can make any further changes?

Thanks in advance.

From the (if your) pump curves, at 20W & fixed speed 2, you are circulating 12.0LPM (0.72m3/hr) at a pump head of 2.8M, if you change to PP2
then you will circulate 9.8LPM at 1.9M, which may be OK, the power will then fall as the TRVs are closing in, its only the press of a button.

A rad running at 75C/63C, dT 12C, will give almost full output, if you reduce the flowrates still further to give 75C/55C/dT 20C, then the rads will still ouput 87% of their rated output, the TRVs (if) throttling down) will then keep reducing the rads&boiler return temp to give greater boiler efficiency.
It can be quite difficult to get a dT of 20C by throttling the L/S valves, if you leave them as they are now (dT of 12C) and just reduce the flow temp to 65C then the return temp will fall from 63C to 55C, dT 8C, but still gives the same boiler efficiency BUT the rad outputs will then fall to 75% of their rated output, probabl still OK most of the time and 65C should still be OK for heating your HW cylinder.. The TRVs will again achieve greater boiler efficiency when the outside temperatures rise requiring less rad output.

 

[Andy B 23]

Andy! For condensing boiler the difference is 20 degrees. For old cast iron it was 11 degrees.

You could reduce pump speed further and see what happens.
Are you balancing the system with cylinder also calling?

Hi DP, thanks for the response, no HW demand off at the time of balancing the rads.

 

[Andy B 23]

From the (if your) pump curves, at 20W & fixed speed 2, you are circulating 12.0LPM (0.72m3/hr) at a pump head of 2.8M, if you change to PP2
then you will circulate 9.8LPM at 1.9M, which may be OK, the power will then fall as the TRVs are closing in, its only the press of a button.

A rad running at 75C/63C, dT 12C, will give almost full output, if you reduce the flowrates still further to give 75C/55C/dT 20C, then the rads will still ouput 87% of their rated output, the TRVs (if) throttling down) will then keep reducing the rads&boiler return temp to give greater boiler efficiency.
It can be quite difficult to get a dT of 20C by throttling the L/S valves, if you leave them as they are now (dT of 12C) and just reduce the flow temp to 65C then the return temp will fall from 63C to 55C, dT 8C, but still gives the same boiler efficiency BUT the rad outputs will then fall to 75% of their rated output, probabl still OK most of the time and 65C should still be OK for heating your HW cylinder.. The TRVs will again achieve greater boiler efficiency when the outside temperatures rise requiring less rad output.

Hi Johntheo5, many thanks for this detailed response, I am now fairly happy with my rad balancing so as suggested I will now look at playing around with the pump speed & boiler flow rate to see what I can achieve while still keeping the boss warm enough & heating the water to a suitable safe temperature, talking of which I have tested the water temp at the taps & it is currently 55 degrees which I understand is acceptable?

The advice & guidance received from this forum over the last couple of days has been excellent, thanks to all who are taking the time to respond.

 

[DP]

That boiler needs regular thorough examination where I would remove the fan, burner and insulation between the two halves of the heat exchanger. The panel seals and flue seal also fail As does the big O ring seal on the sump. Random lockout also a pain. Start saving up on a replacement.

 

[Andy B 23]

That boiler needs regular thorough examination where I would remove the fan, burner and insulation between the two halves of the heat exchanger. The panel seals and flue seal also fail As does the big O ring seal on the sump. Random lockout also a pain. Start saving up on a replacement.

Thanks DP, yes if this boiler was in Yorkshire I am sure it would have worn out by now, thankfully the milder climate in Devon means that it is not on 24/7.