Thanks for that Bunnyman. I did get a heating engineer to diagnose and do the work - he said it was the expansion vessel - so ordered the part and fitted it - i did look at your responses to other issues and tried to tell him what i had read but he said he knew what he was doing but no i am...
Help Vaillant 831 boiler F.75 fault and rising pressure. 1st I changed the Pressure sensor - worked no more F.75.. 2nd rising pressure so fitted a new expansion vessel - Pressure rises from low in the grey to max in approx 1 week. Have i missed something - should i pressure the new internal...
