I have got a Trianco Eurostar boiler, and have been recently
experiencing some weird behaviour, such as, in the middle of the night
the boiler switches itself on.

The CH system has a programmer, which is working fine, and a room
thermostat which again is working fine. The boiler is located in the
house (utility room) and there is no frost stat fitted.

If the system kicks in in the middle of the night, ie even through the
programmer is switched off, the only way I can stop it is to either
switch of at the mains, or to turn the boiler thermostat right down.

First question is: Is this normal behaviour? (I assume not as I feel
the programmer should be the deciding factor)
Second is: What can I do about it?

Thanks for your thoughts.