Return flow temperature too high?

[John Driscoll]

Main 18 Heat ERP boiler. Wiser smart TRV controls. Drayton Auto balance thermostatic valves.
I'm having problems maintaining good flow around CH system. The out flow is 60c and return is 55c. As a result the boiler is reaching set point and switching off before rads get hot enough. I've replaced the flow thermistor and tried different pump speeds. I've been advised I probably have a blockage somewhere but don't want to involve a power flush unless I'm sure. Any help would be greatly appreciated.

 

[gmartine]

Have you set the auto balancing valves correctly (rad size and flow rate)?

 

[ShaunCorbs]

You tried removing the smart trv heads ?

 

[John Driscoll]

Have you set the auto balancing valves correctly (rad size and flow rate)?

I've found the Drayton guide a bit vague. My radiators are Revive column type. The chart lists all the sizes and outputs but calculated at Delta 50. The Drayton chart lists all outputs but 3 settings for delta 10,15 and 20. I'm assuming there would be an adjustment for the correct value but i'm not sure how to proceed. I've always thought the Delta value is something you end up with rather than something you can set.

 

[ShaunCorbs]

Delta 20 set them for

 

[Chuck]

A few questions:

1. Where are you measuring the 60/55 flow/return temperature? If these are the values reported by the boiler, what are they further away?

2. How long does the boiler take to "[reach] set point and switching off before rads get hot enough"?

3. Is(are) there any radiator(s) that do get up to temperature in the process?

4. Has the system ever worked correctly? Did it stop working abruptly or over a long period of time? Have any modifications, e.g. new valves, been made since it was last working correctly?

 

[John Driscoll]

A few questions:

1. Where are you measuring the 60/55 flow/return temperature? If these are the values reported by the boiler, what are they further away?

2. How long does the boiler take to "[reach] set point and switching off before rads get hot enough"?

3. Is(are) there any radiator(s) that do get up to temperature in the process?

4. Has the system ever worked correctly? Did it stop working abruptly or over a long period of time? Have any modifications, e.g. new valves, been made since it was last working correctly?

1. Measuring at boiler. Further away typically delta 10.
2. The boiler is cycling every 4-5 minutes and only switches off when there are no TRVs calling for heat.
3. The ones nearest the boiler get very hot.
4. Its never really worked properly, that's why I've added auto balancing valves and smart TRVs. I've got the auto balance values set for delta 10. Maybe first set for delta 20 as advised by one member.

 

[Chuck]

1. Measuring at boiler. Further away typically delta 10.
2. The boiler is cycling every 4-5 minutes and only switches off when there are no TRVs calling for heat.
3. The ones nearest the boiler get very hot.
4. Its never really worked properly, that's why I've added auto balancing valves and smart TRVs. I've got the auto balance values set for delta 10. Maybe first set for delta 20 as advised by one member.

AFAIK, the minimum output of the Main Heat 18 ERP is 9 kW so, if the demand from the radiators is less than this then the boiler will cycle. This is normal behaviour for modern boilers and is very noticeable when the weather is mild. Individual 'smart' TRVs calling for heat in an uncoordinated manner can make things worse. So too will setting delta T too high on each radiator.

Briefly, a solution to cycling is to use some combination of (a) weather compensation to control the boiler, (b) balance the system so that the TRVs are normally all open and and only close to compensate for solar gain on a sunny day, and (c) a buffer volume to increase the heat capacity of the emitter zone.

If you use the TRVs to shutdown the radiators that currently get 'very hot' does that allow others to get hotter?

 

[Last Plumber]

AFAIK, the minimum output of the Main Heat 18 ERP is 9 kW so, if the demand from the radiators is less than this then the boiler will cycle. This is normal behaviour for modern boilers and is very noticeable when the weather is mild. Individual 'smart' TRVs calling for heat in an uncoordinated manner can make things worse. So too will setting delta T too high on each radiator.

Briefly, a solution to cycling is to use some combination of (a) weather compensation to control the boiler, (b) balance the system so that the TRVs are normally all open and and only close to compensate for solar gain on a sunny day, and (c) a buffer volume to increase the heat capacity of the emitter zone.

If you use the TRVs to shutdown the radiators that currently get 'very hot' does that allow others to get hotter?

What does AFAIK mean?
Just curious.
Thanks.

 

[Chuck]

What does AFAIK mean?

"As far as I know"

 

[Last Plumber]

"As far as I know"

Aha!
Brilliant, I will add that to my personal shorthand that no-one else understands except me. Which is more often than not a good thing.