Valliant Boiler ecotech 832- Heating Partial Load

[SpecialK]

Can you feel / measure the temps on the flow and return? Do they feel like they are 4 degrees apart? If the return is cold then the bypass is letting by inside the boiler. Happened on mine when the UFH circuit was on so I put the bathroom rad on the same circuit which cured it.

 

[Johntheo5]

Maybe wrong but I'm thinking my issue is too little pressure / flow too fast so radiators are not taking enough heat out the water hence dT too low.
[/QUOTE]

I can say for sure that the lower the dT for any given flow temperature and required room temperature then the greater the rad output, basically because the mean rad temperature is greater with a lower dT, so gretaer rad output.
Few examples below,

1.0kw (T50) rad.
20C required room temperature.

Flow.DegC/Return.degC/dT.deg.C/flowrate.LPM/Radoutput.kw
75C/65C/10C/1.433LPM/1.0kw
75C/55C/20C/0.625LPM/0.87kw

60C/50C/10C/0.902LPM/0.63kw
60C/40c/20c/0.367LPM/0.51kw

 

[Johntheo5]

.
Then D172 is dT, D173 is minimum dP and D174 is maximum dP.
When in dP D171 sets target dP - range 100 - 400 mbar.

With dT set dP is in the background with a minimum setting of 100mbar. I think for my system once stabilised achieving dP of 100mbar is what is in control.

Have you tried are are you running in temperature spread mode dT172, where, I think, the dT can be set between 10C & 20C. a friend of mine tried this but it didn't seem to work, he couldn't achieve a dT of 20C, but maybe he didn't set up all the parameters correctly.

 

[Delta925]

I can say for sure that the lower the dT for any given flow temperature and required room temperature then the greater the rad output, basically because the mean rad temperature is greater with a lower dT, so gretaer rad output.
Few examples below,

1.0kw (T50) rad.
20C required room temperature.

Flow.DegC/Return.degC/dT.deg.C/flowrate.LPM/Radoutput.kw
75C/65C/10C/1.433LPM/1.0kw
75C/55C/20C/0.625LPM/0.87kw

60C/50C/10C/0.902LPM/0.63kw
60C/40c/20c/0.367LPM/0.51kw

Taking your second pair of readings with 60C boiler output while a 10C dT gives a greater heat output as I understand with 50C return the boiler will only be just be into the condensing zone while at 20C dT it will be well into the zone so will, or at least should be, more efficient.

This does of course presume that the lower output from the radiator is adequate.

Have you tried are are you running in temperature spread mode dT172, where, I think, the dT can be set between 10C & 20C. a friend of mine tried this but it didn't seem to work, he couldn't achieve a dT of 20C, but maybe he didn't set up all the parameters correctly.

This is how I have currently set my boiler with dT at 15C. I can only get a dT of 10C though.

I maybe wrong but am presuming this is because as I interpret the boiler will only run in dT control if dP is greater than 100mbar but as set my system has dropped to 100mbar dP.
As I posted already to try and prove this given time I will close the lockshield valves more to increase both dT across each radiator and the system dP. The opportunity may not be until between Christmas and New Year. I accept the heat output may well be too low. If so this points to needing larger / greater output radiators. As I stated above non of the installers who visited and quoted mentioned / suggested replacing the radiators.

Replacing the radiators of course has a cost. If the cost was £1000 I wonder if this would this be paid back over time by the boiler running more efficiently and / or working better so increasing reliability and lifespan.

With my previous system of a simple boiler delivering around 12kW or nothing set by the cut-out and cut-in temperature thresholds of the the control board and a pump with two fixed speeds and set to the lower one I could never achieve more than around 8C despite the ideal being 10C - 12C.

... Looking at the manual I can not see a Dxxx code for modulation but I thought I had seen it and recall with 60C output temperature achieved it was 18%. ...

I have now found this.
Once in Installer mode the first menu is ' Data overview '. After selecting this and scrolling through ' Target Modulation ' is shown. When I looked it was 18%.