Boiler on constantly

TheGreenFrog

I have an oil-fired boiler.  Recently it has been on constantly, even though the timer is switched to the off position.  There is a frost thermostat which I thought might be the problem and so I replaced it but it made no difference.  I have switched off the boiler itself but the central heating pump still runs so I am therefore assuming the that timer must be faulty, but wonder if I am missing some other potential issue?  

ThisIsWeird

Type of system? I presume it ain't a combi, and you have a hot water cylinder? In which case you'll have a motorised valve or two, probably located near the cylinder. One of these could be stuck open, therefore telling the boiler to run. Or, the wee switch inside it could be faulty and ditto.

When your boiler was running, what heated up - your rads or your hot water, or both?

What type of timer do you have? Does it appear to work ok - does it 'click' positively when you turn it on and off, and do any indicator lights come on/off to confirm?

TheGreenFrog

It's a big system with 7 motorised valves - six are easily accessible and one not so easy.  So if the zone valve is faulty it will override the timer? Timer seems to be working OK.  I'll try to track down which CH zone or water tank (there are two separate hot water systems - one pressurised and one gravity - for complicated reasons) is heating up.  I have changed head units before (but in those cases the valve was stuck shut) so hopefully that is the issue and the faulty one is not the inaccessible one......

molerat

So if the zone valve is faulty it will override the timer?

It is the microswitch in the zone valve, which has permanent power, that calls for heat triggering the pump and boiler, the timer simply tells the zone valve to open and clicks the microswitch.  A failed microswitch, stuck open valve or water leaking from the valve into the head can cause the spurious call for heat.

TheGreenFrog

Thanks - it may well be a switch then as all the valves appear shut (I took the head units off) and so all that is heating up is a towel rail circuit which is not controlled by a zone valve (it just heats up whenever the boiler comes on for hot water or central heating).  Sounds like I need to find a CH engineer (hens teeth where I live) as don't know how to find which valve might have the faulty switch and I don't want to do a trial and error switch of each unit.

Veteransaver

It hasn't got a test switch on it (maybe inside the cover) which has been inadvertently turned on has it?
It could be one of the zone valves though, sticking microswitch. You may need to replace the motorised head, its relatively simple, no plumbing, just wiring the new head in.

TheGreenFrog

Veteransaver said:

It hasn't got a test switch on it (maybe inside the cover) which has been inadvertently turned on has it?
It could be one of the zone valves though, sticking microswitch. You may need to replace the motorised head, its relatively simple, no plumbing, just wiring the new head in.

The problem is I have seven valves so it is knowing which one is faulty without doing a trial and error replacement one by one. Will have a look for test switches although can't think how the swicth (if there) would have been switched on.

Rodders53

Microswitch in head stuck in and 'on/call for heat' is common place.

Usually when one operates the manual levers to open the valve one can hear the microswitch click on, and click off as the spring returns the arm and valve closes.

The stuck on one might not click... and then you have your most likely suspect.

If you've changed heads you'll have been in the wiring centre(s) to do so... so must be "competent" to DIY work on the electrics
Lifting individual motorised heads' 'call for heat' wire (parked into a temporary connector block) could also identify the six that are OK and the one that is stuck on and calling.  Taking all the usual precautions (isolating mains, do a 'test' wiring change, only then re-power etc.,.)  

Repair is clean up a mechanical stickiness, replace the microswitch, or the complete head unit).

Calling in a heating electrician will cost in the time taken to do something very similar to the above process I've described to identify which one is faulty.  

ThisIsWeird

SE7EN motorised vales?!!! Hell's teeth, man

How is each one controlled - individual room stats or what? I guess two will be for the DHW systems? They'll have timers?

Assuming they are 'normal' motorised valves like ordinary folks have, you go to each one in turn, first try moving the manual lever through its full travel, and listen for a 'click' at the end of travel. It's possible that the 'manual' travel won't quite make the microswitch go 'click', so if you don't hear a 'click' then ask someone to turn on the controlling thingy for that valve. Listen closely - it should 'whirrrr' smoothly for 2-3 seconds, and end with the desired audible 'click'. Then shout at the person to 'turn it off', whereupon it should 'click' again and whirr back to the standby position.

Move on to the next one.

Do them all.

In fact, if you have a helper, do them all by asking the helper to 'turn it on'.

Then go back to the 'dodgy' one - the one that wasn't decisive - and hit it with a lump of wood. See if the boiler now turns off.

It's all very scientific.

TheGreenFrog

ThisIsWeird said:

SE7EN motorised vales?!!! Hell's teeth, man

How is each one controlled - individual room stats or what? I guess two will be for the DHW systems? They'll have timers?

Assuming they are 'normal' motorised valves like ordinary folks have, you go to each one in turn, first try moving the manual lever through its full travel, and listen for a 'click' at the end of travel. It's possible that the 'manual' travel won't quite make the microswitch go 'click', so if you don't hear a 'click' then ask someone to turn on the controlling thingy for that valve. Listen closely - it should 'whirrrr' smoothly for 2-3 seconds, and end with the desired audible 'click'. Then shout at the person to 'turn it off', whereupon it should 'click' again and whirr back to the standby position.

Move on to the next one.

Do them all.

In fact, if you have a helper, do them all by asking the helper to 'turn it on'.

Then go back to the 'dodgy' one - the one that wasn't decisive - and hit it with a lump of wood. See if the boiler now turns off.

It's all very scientific.

They are all controlled by manual switches next to the programmer.  Rads are all thermostatic valves.  I will try the suggestions above! 

TheGreenFrog

Rodders53 said:

If you've changed heads you'll have been in the wiring centre(s) to do so... so must be "competent" to DIY work on the electrics
Lifting individual motorised heads' 'call for heat' wire (parked into a temporary connector block) could also identify the six that are OK and the one that is stuck on and calling.  Taking all the usual precautions (isolating mains, do a 'test' wiring change, only then re-power etc.,.)  

Repair is clean up a mechanical stickiness, replace the microswitch, or the complete head unit).

Calling in a heating electrician will cost in the time taken to do something very similar to the above process I've described to identify which one is faulty.  

My previous changes were on a far simpler system!