Central heating sysytem tripping electrics during off period

[Steelman]

I have a heating system using a Thorn programmer which is identical to the Honeywell ST699. On occasions, at the same time in the early hours the socket breaker is tripping and will only reset once the power to the heating system is switched off. In the morning the system will be allowed to switch back on and it will be ok for another week or so.
Any ideas, could it be the timer as it is the only part taking power at that time

 

[Softus]

Could be many things, but likely to be either boiler or pump.

Which boiler do you have?

Have you checked for leaks around the boiler and in the airing cupboard?

 

[Steelman]

The boiler is a Thorn Apollo. I have checked and there is non sign of a leak. The boiler is in the airing cupboard.

The pump is a Pegler Terries and is only 2 years old, it seems to be operating normally.

 

[Dan Robinson]

Zone valves? how many? where are they? bet there is a drip landing on one somewhere...