A mystery for me

[regsmyth]

External oil boiler. Pump, valve and timer in airing cupboard.

Heating has been working fine.
Went away for two nights, came back to a cold house.
Room stat and timer calling for heat but nothing firing.
Flicked switch in external boiler and all started working again.
(The illuminated switch on RH side of black box).

(Not sure what switch is for but I assumed it was a lockout and something mysterious had triggered it).
But later, after timer had switched off, pump was still running and boiler was still firing.

Does anyone know what the switch is? (I'm now assuming it overrides timer and room stat).

Does anyone have any clues what might be the problem?

Thanks for any thoughts.

 

[slapper]

That switch provides a permanent live to the boiler, it overrides programmer etc

Your internal controls will be causing the problem, that switch will keep boiler running 24hrs and only switch off when Boilers reached temperature

The idea of the switch is to allow servicing to be done without using internal controls

 

[regsmyth]

Ok thanks for the info. It all seemed to work again this morning, so I'll keep my eye on it. I'm sure somethings not right though - as you say, maybe a wire's popped out somewhere...