Oil boiler on when control switch is off

[hedgert]

I've recanted moved into a house with an Aga and separate oil boiler for heating and hot water.
Both work, but the boiler spends much more time on than I would expect and keeps pumping hot water through the radiators long after the time/control switch has switched off.
I've not had an oil boiler before - is there anything fundamentally different about the way it works compared to a gas boiler? Does it for any reason need to remain on/heating when hot water/heating is not required? Would you expect it to continue to pump hot water through radiators even when the control switch shows hearing turned off?

 

[keltoyboy]

sounds like you have possibly got a frost stat which may be set too high....this will override your controls ....really need some more info....boiler make/type /is it an indoor or outdoor etc etc!!

 

[hedgert]

Thanks for the quick reply - agree not much data to go on! Here's some more:
The boiler is indoors - info plate attached as first photo
It's a Trianco Eurostar 180. It's in a cupboard in the utility room against an outside wall with the flue on the outside of that wall.
It has several pumps (at least I assume that's what they are) piped above it:

There are two thermostat controls on the wall outside the cupboard it's installed in - one is the conventional heating controller/timeswitch that I'm using:

The other is a frost stat. When we asked the previous owners about it they said they never used it and suggested it didn't do anything. But I'm interested that you mention a frost stat when I gave you so little information - given that the boiler is inside the house I wasn't clear what a frost stat would be protecting from frost - is it the pipework that goes outside to the tank or something? The frost stat is set at absolute minimum - so I assume it wouldn't be doing anything - unless it's broken. And when I rotate it to see where the thermostat switches, it clicks in the room temperature range so I'd assume that the sensor it's using is inside the house - and again wasn't clear what a frost stat would be used for in this situation.

 

[keltoyboy]

OK frost stat would be used if you were away over the christmas and even though you did not leave any heating timed to come on, the frost stat would do that if the temperature fell low enough around where the stat is positioned...
You say you have several pumps.... i can only see one in the pic and the controller is only a two channel so i think you may be referring to the silver boxes which are motorised valves....another possibility that a faulty one of these may also be calling for heat when it shouldn't.....if you have a volt stick you could check if there is power coming from the frost stat or a motorised valve next time boiler fires up without any input from the controller!

 

[hedgert]

Thanks for your help keltoyboy. The frost stat has no voltage on it at all on or off - so I think it is old/disconnected. Thanks for the guidance I can see the single pump/multiple valves now you've pointed them out. I need to get the firm that has maintained the boiler for the previous owners in for something else so will get them to look at the persistent on problem when they come. Appreciate your time in giving information/suggestions.

 

[SimonG]

Sounds like a motorised valve head problem.

 

[WHPES]

Had something similar a couple of weeks ago and called in my spark (it wasn't a valve actuator). The electrician found that a permanent live supply to a valve was faulty causing it to stay open when the thermostat switched off.