Our boiler is trying to start itself up randomly. It's 4 years old and so far we have had no problems.

Now it goes into the start sequence, lights the burners then shuts down. It repeats this at random throughout the day.night.

It does this, whatever the controller is set to, even with both CH and Hot water off.

Any suggestions what diagnostics I can try before I call out the expensive man

Slatz, June 2008

Looks like the switched live (SL) terminal on the boiler is permanently live. It should only be live when the controls or the frost stat (if fitted) call for heat. If you're comfortable with testing mains electrics, use a suitable mains tester to test this terminal when the system is not calling for heat. If it's live, try disconnecting the incoming wires from the terminal and test them one by one to see where the rogue live feed is coming from.

el scripto, August 2008

maybe an unusual pcb problem, but if boiler is 'switched off' it shouldn't fire, it there a frost stat on your system? if so maybe it's faulty and is firing to protect the system.

But in any case with this type of problem you will need to get you serviceman out

T, June 2008