Combi boiler question

[W_sparky_21]

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Got a combi boiler controlled by a Drayton room stat, the one you manually turn the dial round to 30 and the boiler comes on and then turn it round to 10 for it to go off, recently when I turn it round to 10 it goes off but then comes on a minute later and heats the radiators up until they are too hot to touch, only way to stop it is by isolating the boiler at the FCU, any ideas what could be causing this?

 

[telectrix]

broken stat.???

 

[W_sparky_21]

broken stat.???

Could be, it’s not everytime it does it though. Sometimes during the night it will just come on and do the same thing

 

[Paignton pete]

Intermittently broken stat??

 

[static zap]

Is it set to pre-heat hot water from tap ?

If you turn its supply of and on , does the behavior disappear for a while ?
(the other guys will have the answer)

 

[James]

Change stat for a switch
If everything works correctly then the stat was faulty

If still the same problem, could be you have to find a hidden frost stat in a place where it is cold.

 

[240volts]

The thermostat opens and closes the Actuator Valve (Is it Y plan or S Plan ?) you should have a 3 way valve or 2 x 2 way valves controlling the water supply to the boiler and cylinder.
I would suspect ACTUATOR VALVE for heating if its not the thermostat.

 

[James]

The thermostat opens and closes the Actuator Valve (Is it Y plan or S Plan ?) you should have a 3 way valve or 2 x 2 way valves controlling the water supply to the boiler and cylinder.
I would suspect ACTUATOR VALVE for heating if its not the thermostat.

It’s a combi boiler so the above DOES NOT APPLY

 

[PEG]

It’s a combi boiler so the above DOES NOT APPLY

With respect,you could not say that with certainty,without seeing the system,the OP has.

It could be a right old mix-n-match i have seen more than a few combi set-ups,with strange overide switching AND stored hot water.

 

[littlespark]

It’s the old mechanical thermostat with a bi metal strip.... it’s just worn out. Get it replaced.

isn’t there a programmer so you can stop it coming on in the middle of the night?

might be a chance to leap into the 21st century and get one of those new fangled Smart stats....

 

[Leesparkykent]

Are you sure it isn’t a wireless thermostat and the batteries are on their way out?