I switched my boiler off at the control unit. So why does it fire up?

[Jimbo]

I work away during the week, so I turn my HW and CH off at the control unit (Danfoss FP715).

Once or twice I've gotten home at the end of the week and switched CH on to warm the place through, and the boiler doesn't fire, although the radiators tick away and get hot. If I put my hand on the boiler case it's warm. Clearly the boiler is firing up even though it's switched off.

A couple of times I've heard it fire up during the night, even though it's on a timer and most definitely NOT supposed to be on at 2am.

Any ideas?

 

[ianmcd]

sticking end switch/seized synchron motor on one of the zone valves if S Plan or faulty actuator if Y plan, really need more information boiler make and model you may also have a frost stat that is operating

 

[mogget]

Just a hunch, is this a thermal store system?

 

[75pete]

Frost stat?

 

[Jimbo]

It's a Worcester Bosch Danesmoor 20/25. It's just been serviced although I forgot to mention the problem to the engineer.

Where would I find the frost stat and is it an easy job to replace?

 

[ianmcd]

It might be the frost stat but as I already said could also be zone valves or 3 port ,I dont know what system you have as you havent said

 

[rhinosaw]

I'm no expert but have had a similar problem to yours but mainly in the warmer weather. Ch & Hw both turned off at programmer (s plan).
Boiler fires up sporadically for no apparent reason. Turned room stat down to zero, problem solved, realise yours could be a different problem though

 

[stem]

Ch & Hw both turned off at programmer (s plan). Boiler fires up sporadically for no apparent reason. Turned room stat down to zero, problem solved

You haven't really solved anything. The room thermostat should not be operating if the CH is switched off at the programmer. The thermostat should only receive power from the programmer when it is 'on' according to the 'on times' entered. When the programmer is 'off' the room thermostat shouldn't do anything.

Having said that, there is a possible exception. If you have a programmable room thermostat that has been added later, the programmable thermostat can take over the time control functions normally associated with the programmer. In which case the existing CH channel of the programmer may have been disconnected and therefore not do anything. Although if this was the case, I would expect you as the user to know that and not be trying to use the CH channel.

I suspect also, in your case that the radiators are getting hot. With the OP the radiators aren't getting hot but the boiler still is.

 

[rhinosaw]

I understand what u are saying stem.
Nothing added or taken away in the last 20 yrs.
I wired the programmer myself many years ago. Must have miswired it probably.

 

[MeldrewsMate]

Is this Jimbo's thread or Rhinosaw's?