potterton combo boiler only hot water, not central heating..

[disaster_diy]

Hi everybody who can give me a hand.
After one month in the warm Spain I've just come back to England to find out that, thought I can get hot water, the central heater seems to refuse to work at all.
I'm freezing while thinking what has happenned in one month. Everything was fine, then.

I switched off completely the electricity of the house and today I find out the the light of the radiator on doesn't turn on: no noise, nothing.

I have a Potterton performa 28 combi boiler.

The only neon that are on are the power on neon and the flame failure neon (perhaps is only indicator of 30° C?). I have tried to reset the neon without success.
The pressure is OK (2.5 bars).

When I turn on the hot water, the domestic hot water mode and the burner on neons switch on and I get hot water, but no way to switch on the central heating on mode neon before or after the taps are on (I have selected CH/hot water position).

Can anybody give me a light?

Thank you very much.

 

[ChrisR]

This sounds like a problem with the Diverter Valve, which will need to be replaced. The part costs something like £90.