Vaillant Turboxmax 824E Combi

Help!! I have a Turboxmax 824E which is about 3 years old and recently I keep getting a red light come on and the display shows an F28 error. The manual tells me that it's something to do with a 'lock out' but it doesn't tell me how to remedy the problem. I can reset the boiler so that the heating and hot water come on but I've noticed that my pressure gauge is at zero. Does anyone know how I can increase the pressure? Also, my clock on the boiler keeps losing time - any ideas????
Any help would be very much appreciated!

Under the boiler there are 2 small brass valves with a flat screwdriver slot in them. Open them both 90d and this should fill the system. When the needle gets to about the 10 O'Clock position, turn them both off.

F28 can also indicate that the boiler is in need of a good service, the minimum burner pressure drifts out on these, as does the sensing electrode/spark electrode gap.

I think you wil find your boiler is more like 5-6 years old!

If the mechanical clock is losing time then it will have to be replaced.

Tony

Thank you very much for your advice, I'll give that a go