F.28 Vaillant thermocompact boiler will not reset?

this is low water pressure= leak on system or boiler or the PRV has blown off or is leaking.
Just changed a PRV on a thermocompact and this cured the problem first time.

Riverside
May 2011

i don't know if your problem is the same as mine, but i did this and it fixed the problem....
Fault F28
this means drop in the pressure(gas or water, not sure, but probably the gas)... if you see on the boiler panel, there is a gauge measured by Bar... your gauge and pressure must be somewhere between 1 and 2 in the green area. yours is probably well below the 1 Bar(and not in green area) that you get this fault code,F28

to fix this fault, underneath or around the boiler case somewhere, there is a little valve connected to pipe( in my boiler there is just one valve), open that valve carefully while keeping an eye on the Bar Gauge i said earlier. opening the valve MUST increase the pressure and push the gauge to the green area. when the guage hand reached somewhere betwwen 1 and 2, close the valve again and fire up the boiler... it should fix the problem....
hope it helps.

Hadi
December 2010