Vaillant Ecotec plus 637 - Anti cycling

[The831Bunny]

Thanks for your thanks!

Basically if the boiler is reaching temperature before the house does, a few things are happening. The radiators are not sized correctly (too small), the system isn’t balanced correctly (including setting of any external bypass), or the pump is too slow. Now when you drop the Kw output at D.0 the pump speed will be dropped as well, this doesn’t always suit the system, so depending on which year your 637 is manufactured there are two ways to adjust this. Either D.19 (set to 3 (not 2)) or D.14 (set to 5 or 100%). As its a system boiler, I would also recommend you have the flow temperature a bit higher, say 65ºC as it will stop it short cycling too much when heating the cylinder, which I presume you’ve got set to 50-55ºC?

There are other factors, but its best to try these things one at a time.

Let us know how you get on.

 

[RK_London]

The cylinder is set between 50-55 C. The 637 was fitted in 2019. D19 is the pump operating mode and is set to 2 - stage pump - auto. Setting it to 3 sets operating mode always to stage pump. What does always setting to stage pump (3) do versus auto (2)?

 

[The831Bunny]

If it is a 2019 637 then the pump speed is set on D.14. Set it to 100% and see what the temperature difference is on D.40 and D.41 after 5mins

 

[RK_London]

Set D.14 to 100% and the temperature difference is 5C after 5 mins. Goes into pump over run after about 5 mins in burner mode. Room thermostat has been reached and been steady for several hours

 

[The831Bunny]

That sounds good. By saying 5mins I’ve allowed for the low rate at start up to ramp up to the 15Kw set on D.0. Have a look again when the burner is on and the flow temperature is around 55ºC. Otherwise you’re there I’d say.