Vaillant Ecotec plus 637 - Anti cycling

[RK_London]

Boiler goes into anti-cycling mode for a few minutes at the end of each cycle after pump over-run. Does anyone know if it's normal or whether I need to make adjustments to my heating set up

 

[muggles]

Probably massively oversized for the system. How many radiators do you have / what's the floor area of your house?

 

[RK_London]

I have 15 radiators and the floor area of the house about 1800 square feet. Had the boiler changed about 2 years ago. Added an extension with two extra radiators and the boiler went from 28KW and 37KW. Installer insisted it was justified although I do agree with you that it is oversized as I have the power set to just 18KW.

 

[RK_London]

Should I leave heating set up as it is or should I make any adjustments?

 

[ianmcd]

Try taking the heating load down to 15KW and see what changes, you can always put it back to 18KW , I bet you dont use all 15 rads all the time

 

[RK_London]

You are right - I don't use the radiators all the time particularly with insulation being so good in some rooms that some radiators not switched on next day. I will take heating load down to 15KW. I also saw a max anticycling time of 20 mins (default setting). Should I leave that alone? I saw a table of target flow temperature vs max anticycling time - didn't quite understand what the numbers in the table showed.

 

[ianmcd]

I wouldnt be altering the anticyle at this point, what is the target temp on the boiler set to for CH ?

 

[RK_London]

60c

 

[ianmcd]

Yes that should be fine, some people always run at max which can cause problems on some systems

 

[RK_London]

thanks for your help

 

[RK_London]

Power reduced to 15kw and still getting anti-cycling for a few minutes at the end of each cycle. Should I reduce power further?

 

[ianmcd]

wont do any harm, the lower you take it and everything still hot enough the cheaper it is to run, but nearly all boiler have anti-cycing of some sort some are fixed time some are temp controlled like yours, it is a perfectly normal function, not a boiler fault, reduce the power , you can always put it back up if you are cold

 

[RK_London]

Reduced power to 13KW and anticycling has disappeared. Radiators working well.

Have a more general question about boiler cycling. If the weather outside is really cold (say -30C) and my house has lots of heat loss, the boiler will have constant demand for heat. Does that mean that if the weather was -30C forever the boiler will never cycle beyond burner mode and never go into pump overrun?

 

[The831Bunny]

You’d be better extending the pump over-run time to exceed the anti-cycling time. That way the pump runs till the next firing request, instead of stopping after 5mins and the boiler sitting there in anti-cycling. If D.2 is set to 20 that gives an anti cycling time of at least 6mins at 60ºC, extend D.1 (pump over-run to 8mins and your system will run a bit better. As ianmcd said take D.0 down to a level where you still achieve the required property temperature. A good rule of thumb to check system load is to check D.40 and D.41 (flow and return temperatures), After 7-10 minutes from a cold start when the flow temperature is up to 50 the difference should be at least 12ºC, ideally 15ºC but no more than 20ºC.

Hope that makes sense

 

[RK_London]

Thanks - extending the pump over-run slightly was exactly what I ended up doing to avoid sitting in anti-cycling. The pump over run is set at 7 mins. D.0 is set at 15KW and everything works well now.
Only thing I'm trying to understand is why once target flow temperature is reached, temperature begins to drop as though initial heat demand has been satisfied even though the boiler thermostat temperature is not achieved. For example if I set room thermostat to 21C boiler fires up to set target temperature of 60C and room heats up but at about 20C and flow temperature drops to say 40c. Would have thought this would happen at 21C. Only happens sometimes so I can live with it.