Vaillant EcoTec Plus 938 temperamental in heating mode

[John.g]

This boiler even with a big call for CH Iwhere the bypass would/should be shut in any case if installed only occasionally gets up to 60C so maybe some other problem. One of the main reasons for a external bypass is to dissipate some heat with boiler shutdown and pump overrun, another is to keep the flow/return < Say 30C with very low circulation flows. Some boilers, probably with SS HXs don't require them. ABVs don,t work with modulating circ pumps IN PP mode and need very careful adjustment with pump in CP mode hence the recommendation above for a manual bypass.

 

[skvortsov]

Internal bypass is fine, you won't need an external one. That's what it's there for.

I'd set your pump to 100% on d.014 and it maybe that you bypass wants adjusting internally on the boiler, which your plumber will need to do.

And put Partial load back to Auto.

Thanks a lot! Looks like this solved the issue - added 1 full turn on the internal bypass, set output to Auto and now it goes to 60 degrees flow straight away! And now it's wired in a way that radiators zone valves open when UFH is ON to make sure that there is some flow through towel rads (we have 3 of them). So I believe it will be ok without additional bypass

 

[EvilDrPorkChop]

Thanks a lot! Looks like this solved the issue - added 1 full turn on the internal bypass, set output to Auto and now it goes to 60 degrees flow straight away! And now it's wired in a way that radiators zone valves open when UFH is ON to make sure that there is some flow through towel rads (we have 3 of them). So I believe it will be ok without additional bypass

No problem

 

[John.g]

Thanks a lot! Looks like this solved the issue - added 1 full turn on the internal bypass, set output to Auto and now it goes to 60 degrees flow straight away! And now it's wired in a way that radiators zone valves open when UFH is ON to make sure that there is some flow through towel rads (we have 3 of them). So I believe it will be ok without additional bypass

That's great to hear, you suspected the flow rate originally,
It would be interesting to see if you now can on UFH only or rads only

Did you also increase the pump speed to 100%?,
Also if you get a chance you might post the flow and return temps.

Thanks.

 

[john G]

That's great to hear, you suspected the flow rate originally,
It would be interesting to see if you now can on UFH only or rads only

Did you also increase the pump speed to 100%?,
Also if you get a chance you might post the flow and return temps.

Thanks.

Can't log in on this PC for some reason or other.

 

[John.g]

Why do I have to reset my password each time I log out since this morning?.

 

[king of pipes]

Why do I have to reset my password each time I log out since this morning?.

One for Shaun John ????

 

[ShaunCorbs]

Please define reset ? You have to change it every time you try and log on ?

 

[John.g]

If I log off or just exit the forum without logging off and go back in it asks me to log on, it then displays my user name and saved(correct) password but when i select log in nothing happens so I then select "forgot password" it then directs me to my given email and asks me for new password + confirmation, I then enter my (saved )+confirmed) password and press save and I am then logged in, the same happens in the central heating forum but not in the Electrical forum (different user name).

 

[skvortsov]

That's great to hear, you suspected the flow rate originally,
It would be interesting to see if you now can on UFH only or rads only

Did you also increase the pump speed to 100%?,
Also if you get a chance you might post the flow and return temps.

Thanks.

Pump was always at 100%. Will post some charts on temps later