mains pressure lower than minimum combi system pressure

[Andrewww]

We have a vaillant combi boiler that over ~ 2yrs loses a bit of pressure, and recently after 2 weeks away and no use the system would not fire and errored with F75.

We attempted to refill, but the mains pressure is only 1.0bar, and the combi needs more than that to light.

I ended up removing the front cover, letting air out the expansion vessel, refilling to main pressure of 1 bar and then pumped up the expansion vessel again.

A bit of a faff, and there must be a better way of getting the system pressure up rather than this bodge?

 

[Deleted member 120897]

Oh dear, F75 can be a couple of things but usually one main culprit. Did you leave a drain point open when you pumped the expansion vessel back up? Most Vaillants I know of will work at 1 bar pressure. Did you carry out a 26.9 check after removal of the cover?

 

[ShaunCorbs]

As above 1 bar is more than enough vallants cut out at 0.8 bar so need to be above that