No central heating, boiler not starting. Hot water works.

[SDB]

Boiler - HeatRae 75/100.
Control unit - Horstmann H27. The old timer controls in the Boiler are set to continuous.
2 x Tower 2 port valves (heating)
1 valve (hot water)
2 x Room thermostats (honeywell).
(The lounge is on its own heating circuit hence 2 x port valves and room stats).

Problem - Heating is not coming on, boiler is not firing up, pilot is lit.
Timer is on and neon light showing, room thermostats are turned high.

Hot water is fine.

Heating was not working yesterday, came on this morning, now stopped working again.
I can confirm valves open and close when heating came on. Adjusting room stats turned heating off.

Any ideas? If its the timer I can replace that but cannot find anything on the internet to tell me how to check it rather than just spending £50 for a replacement.
If it is anything else I will have to get someone in.

Thanks.

 

[seco services]

if none of the heating is working then i would check the programmer heating on is giving a live to the stats. check in your wiring cente.