Powermax 185 Central Heating won't work but hot water will

Hi

I have a Powermax 185 Boiler, and the central heating suddenly won’t work. I’ve followed the fault rectification instructions but it won’t operate.

When selecting the Operating Switch to Hot Water Cont. I can get the system to provide hot water, but when selecting Timed, neither the HW or CH will work. The boiler is now 13 years old but we've had no issues like this previously.

Can anyone help?

Thanks for your assistance
Andymac