Radiators Hot When Both Water and Heating Off

weby72

Hi. I'm looking for some advice on diagnosing what's wrong with my central heating system.

I have a Glow Worm Flexicom 30sx boiler running a sealed system. There are two 2-port motorised valves in the airing cupboard. The timer is a Drayton LP722. The boiler was new in 2011 and the system hasn't been changed since the house was built in 2004.

We have the hot water on from 6 in the morning through to around 9pm. Heating comes on for a couple of hours in the morning and several in an evening.

Two days ago, I noticed the radiators were very warm (not full-strength hot) during the day when the CH was off. Same happened yesterday. After looking around online, the most likely issue was that a 3-port motorised valve was stuck open and supplying hot water to both the tank and the CH (I hadn't checked that I had a 3-port, just assumed; now I realise I have two 2-ports instead).

Then last night, I woke feeling really warm. And wanting a wee (I've reached that age ). When I went the loo, I felt the radiator and it was 'very warm'. I hoped it was after 6am and was just the hot water 'leaking' into the CH system. But it was 3.30am. I went down to check the boiler and it was fired up - but the timer unit was showing both HW and CH as being off. I also remembered the boiler firing up around 11pm the previous night when, again, both HW and CH were showing as off. The rads are still getting warm today with just the HW on (and CH off)

I've since turned the HW and CH off on the timer, and the boiler does still fire up again.

So the problem is the boiler operating/firing up when the timer is supposed to have turned the HW and CH off.

Can anyone shed any light on what the problem could be caused by?

JGB1955

It's likely to be a problem with your three-way valve.

weby72

JGB1955 said:

It's likely to be a problem with your three-way valve.

I don't have a 3-way valve. I have two 2-way valves.

parcival

Have had similar recently. Changed the 3 way valve but made no difference. Eventually tracked down to a faulty froststat as our boiler is in the garage. Do you have a froststat? 

nofoollikeold

1. I would expect the problem to be with the two way valve on the central heating side.
2. Systems generally work like this:
2a. Programmer enters an "On" period and sends 240 volts to room thermostat.
2b. If room thermostat decides room needs warming, it switches on and send 240 V to motorised valve.
2c. Motorised valve opens.  At the end of its motoring travel it actuates a microswitch.
2d. Microswitch sends 240 V to boiler and it fires and switches on the pump.
3. So if the microswitch in the motorised valve gets stuck, the boiler will fire continuously.
4. Remedies:
4a. If the actuator head on the motorised valve is replaceable, and most modern ones are, replace actuator head.  Purely mechanical / electrical, no need to get wet.
4b. If the actuator is not replaceable on its own, new valve.  This requires a (possibly partial) drain down.
4c. Both require the boiler and wiring centre to be electrically isolated.  Fit the new actuator (or valve), then cut the wires of the old one in the wiring centre, close to where they are attached, but leave an inch of wire with coloured insulation still in the terminal socket.  The, one at a time, replace the stubs of coloured wire with the same coloured wires from the new valve, removing the stub.  Take a good photograph of the wiring centre so that you can replicate all the connections if anything goes wrong.

Slinky

I'm wondering what you are doing that requires the hot water to be on all day?

Jeepers_Creepers

Almost certainly as NFLO says - it's a faulty CH 2-port valve.

Weby, are you up for a bit of DIYing, or is it 'plumber' time? Ideally you want the whole valve replaced since the valve part also wears out over time, but just the head for the moment will likely sort it. (But buy a complete unit, and keep the valve body for later).

How to check? I dunno - perhaps the next time it heats the rads when not asked to, give the CH valve a good thump with a piece of timber - see it that makes it behave...

You can also check it by getting someone to turn the CH demand on and off whilst you listen to the valve - with 'CH' on timer on, someone can turn the room stat up and down. The valve should 'whirrrrr' smoothly and decisively to the open position in around 2 seconds, ending with an audible 'click' as the microswitch is activated (and 'manual' lever on valve goes completely loose across full travel). Ditto in reverse when demand removed - smooth, decisive, 'click' and lever goes back tight and firm against the 'auto' end.

weby72

Slinky said:

I'm wondering what you are doing that requires the hot water to be on all day?

  
Working from home (and having kids at home), I want hot water 'on tap'

Jeepers_Creepers

Oh, if the rads come on when it shouldn't but only when the DHW is also on, then most likely cause is the CH valve letting-by.

I had this exact prob a couple of months back - two zones (two zone valves), one on all day (mum-in-law...) and I suddenly found that the main house's rads were also hot. Replaced the 2-porter, and checked the old one - valve part was really stiff, and motorised head clunky - it clearly wasn't shutting off properly as it should.

Jeepers_Creepers

(The good thing about a sealed system like yours (and mine) is that if you isolate the boiler (F&R pipe valves at the boiler) and depressurise the system (rad bleed screw), you'll likely have very little water loss when you swap them. And it's a job you can do in literally a couple of minutes. Re-use the old nuts and olives (don't remove them from the pipework) and do a quick swap. This works only if there's movement in the pipes, tho'. I ended up having to undo both valves just to allow the shared feed pipe to move enough.

If you do this, clean up the olives and give it and the male threads a smear of Fernox Hawk. Jobbie jobbed.

weby72

nofoollikeold said:

1. I would expect the problem to be with the two way valve on the central heating side.
2. Systems generally work like this:
2a. Programmer enters an "On" period and sends 240 volts to room thermostat.
2b. If room thermostat decides room needs warming, it switches on and send 240 V to motorised valve.
2c. Motorised valve opens.  At the end of its motoring travel it actuates a microswitch.
2d. Microswitch sends 240 V to boiler and it fires and switches on the pump.
3. So if the microswitch in the motorised valve gets stuck, the boiler will fire continuously.
4. Remedies:
4a. If the actuator head on the motorised valve is replaceable, and most modern ones are, replace actuator head.  Purely mechanical / electrical, no need to get wet.
4b. If the actuator is not replaceable on its own, new valve.  This requires a (possibly partial) drain down.
4c. Both require the boiler and wiring centre to be electrically isolated.  Fit the new actuator (or valve), then cut the wires of the old one in the wiring centre, close to where they are attached, but leave an inch of wire with coloured insulation still in the terminal socket.  The, one at a time, replace the stubs of coloured wire with the same coloured wires from the new valve, removing the stub.  Take a good photograph of the wiring centre so that you can replicate all the connections if anything goes wrong.

Jeepers_Creepers said:

Almost certainly as NFLO says - it's a faulty CH 2-port valve.

Weby, are you up for a bit of DIYing, or is it 'plumber' time?

Thanks for the detailed response, NoFool 
And no, Jeepers, I wouldn't be up for trying to replace the CH 2-port valve     I'll give most things a go, but the central heating system scares the bejesus out of me.

Damn. Was hoping it was the timer (I can refit a timer  )