Boiler firing even when off

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Hi folks,

My boiler is firing up at several points throughout the day and night. CH is switched off (as you'd expect - it's July), and HW is scheduled once a day, in the morning.

I've noticed the sound of a pump running in my downstairs WC, which is where all the (boxed-in) pipework from the boiler heads off to radiators and HW cylinder.

My theory is that either the pump is stuck open and that's causing the boiler to fire up to give it hot water, or that the controller has some sort of problem that's causing it to kick in even though the HW cycle is not active.

Any other ideas? Any thoughts on how to diagnose?
 
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You will need to add some more detail, before you can be offered help...

Which boiler, what timer, what thermostats do you have, have you a separate frost 'stat, is it an open vented, what sort of valve(s) do you have 3-port?
 
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It is most likely that you have an S plan system, and one of the zone valve end switches is sticking in the made position, very common , post some pics of what you have
 
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Hi folks, just wanted to follow up. Haven't had the time to look at the problem until recently, and now I'm more confused than ever.

The boiler is a Worcester Bosch unit (Danesmoor 20/25). It's open system (not combi). Pipework is S Plan with Danfoss HPA 2 motorised valves.

I discovered that the valve for the hot water was seized CLOSED. Yet still the boiler was being triggered and the water was being heated.

I've unseized the valve so it moves freely, put the actuator back on and reapplied the power. The pump immediately started and hasn't stopped (two hours later). The boiler was fired up after about 90 minutes. The control unit has both HW and CH set to Off.

So net difference is I've unseized a valve and nothing has actually changed.

This makes no sense to me. Can anybody advise on next steps to troubleshoot this?
 
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you may have unseized the valve mechanically but the switch inside might still be made and thus calling for heat.
what pipes get hot? do the rads get warm?
 
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Hi Stu,

The weird thing is that on the outlet side of the valves, the pipes aren't that hot. Which suggests water isn't flowing. Yet my hot water is, well, hot. Which makes me wonder whether I've got a simultaneous problem with my immersion heater. That's controlled by a Horstmann Electrisaver E30 which I installed about seven years ago.

Rads don't get warm, although I did notice the return spring on the CH actuator is a little weak (and evidence of corrosion), so I'll probably replace the actuator to be safe.
 
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The weird thing is that on the outlet side of the valves, the pipes aren't that hot. Which suggests water isn't flowing. Yet my hot water is, well, hot. Which makes me wonder whether I've got a simultaneous problem with my immersion heater. That's controlled by a Horstmann Electrisaver E30 which I installed about seven years ago.

Turn it off, there should be no need for an immersion heater and it would cost three times as much to heat water as via gas.

You need to ensure your valve actuators are properly working and valves move freely, otherwise your heating will misbehave.
 
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Well yes, as far as I'm aware it IS off. Hence my comment that there may be a problem with it. I'm not using it by choice :D

Edit: Tested, no fault on immersion heater or controller.
 
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You need a multimeter and know how to use it. Isolate the power to the system, disconnect the orange and grey wires from each valve in the junction box. Test for continuity; if you find it then there is the fault.
In freeing the valve, you may now be able to turn the spindle, but that does not mean the valve is opening. The 'weak spring' on the C/H valve may be because that is the valve that is stuck open and causing the boiler to run. You may find you need to replace valve bodies as well as actuators.
 
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I've ordered two new actuators (CH one was a little corroded as I said previously), they arrived today but I haven't had the chance to fit them.

The HW valve was seized closed, but I guess not completely closed because water was still getting hot. Since I freed it up and closed it, HW hasn't been getting hot. Hoping that new actuators will solve the problem.

Thanks all for advice
 
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Ok, replaced both actuators and that's fixed the problem. Thanks to everybody who helped out (y)
 

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