Originally Posted by Lucy-Lastic
We have a Vaillant Ecotec Pro 831 that is just under 2y old and has started to fail and show a F.75 fault on really cold mornings. It does begrudgingly relight (at the moment) and the pressure is good. What could be causing this? What should I do about it - my installer suggested that I should just contact Vaillant...
LOL.....installers fitting boilers that they know nothing about....bang a boiler in and walk away..
Vaillant are a fantastic boiler and were the only boiler make I used to fit. However, there is one boiler that is not as reliable as the rest....and yes its the "pro".. There is a problem with the pump used in that boiler as to save cost Vaillant used another supplier rather than sticking with Grundfoss. So the pump is the weak part and that's the problem with yours.
When it starts the firing sequence the control board monitors the pump speed. The seals in this pump can stick especially in cold weather and it struggles to start up spinning (so sends the code F75)
This code can also appear if the water pressure drops although the control board is so sensitive it will throw the code F22.
The pump needs replacing and now Vaillant have gone back to grundfoss so any replacement will give more years of fault free service