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Thread: Central heating stuck on!

  1. #1

    Central heating stuck on!

    Hi, looking for an advice. I've a call in to a plumber but might be sometime before he can get to me.

    My central heating has started sticking on full blast. Turned the thermostat off, still on, turned the programmer off and still on. The only way Iíve managed to reset is to turn the mains power off and back on and then all is well for a few hours.
    Iím assuming the programmer (timer box) is knackered. Boiler and programmer are two years old

    Any ideas.?

  2. #2
    Master
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    Have you got a tank or combi system?

  3. #3
    Master murkeywaters's Avatar
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    Mine was doing the same and is a tank fed system, it was a diverter valve getting stuck, looks like a rectangular metal box on the pipe work near the boiler.

    If you have a combi then something else I imagine?

  4. #4
    Could be an electrical failure in any of the parts listed, I'm guessing the thermostat.

    Best wait until the guy arrives, they have the test equipment to check these things out.

  5. #5
    Thanks guys, itís a tank system

  6. #6
    Master
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    Quote Originally Posted by awright101 View Post
    Thanks guys, itís a tank system
    Probably just the diverter valve sticking Ďoní

    Very common fault at this time of the year.

  7. #7
    Master blackal's Avatar
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    Quote Originally Posted by CaptainSlow View Post
    Probably just the diverter valve sticking ‘on’

    Very common fault at this time of the year.
    But - the diverted valve switch is dependent on there being a signal from the programmer.

    So - the issue would appear to be in the programmer.

    If it was the thermostat in the room - then switching off the timer on the CH would negate that.


    Google image: Central Heating Y-Plan - you should be able to logically work through what must be wrong
    Last edited by blackal; 22nd November 2019 at 18:25.

  8. #8
    Quote Originally Posted by blackal View Post
    But - the diverted valve switch is dependent on there being a signal from the programmer.

    So - the issue would appear to be in the programmer.

    If it was the thermostat in the room - then switching off the timer on the CH would negate that.


    Google image: Central Heating Y-Plan - you should be able to logically work through what must be wrong
    Thanks, I will look that up

  9. #9
    Master murkeywaters's Avatar
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    Quote Originally Posted by murkeywaters View Post
    Mine was doing the same and is a tank fed system, it was a diverter valve getting stuck, looks like a rectangular metal box on the pipe work near the boiler.

    If you have a combi then something else I imagine?
    Like I said above, it should look like this, my system has 2 but only one plays funny buggers every now and again -



    Where the little slot and lever are is where I squirt a bit of WD40 every time mine plays up, this un-sticks the internal mechanism and allows it to switch. It does have an electrical supply which should be controlled by the programmer, if its stuck open it will continue to tell the boiler to run no matter what the thermostat or programmer say.
    In the past I have stripped it down but you have to isolate everything being an electric fed switch.
    Last edited by murkeywaters; 22nd November 2019 at 18:47.

  10. #10
    Master blackal's Avatar
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    Quote Originally Posted by murkeywaters View Post
    Like I said above, it should look like this, my system has 2 but only one plays funny buggers every now and again -



    Where the little slot and lever are is where I squirt a bit of WD40 every time mine plays up, this un-sticks the internal mechanism and allows it to switch. It does have an electrical supply which should be controlled by the programmer, In the past I have stripped it down but you have to isolate everything being an electric fed switch.
    It still only en-passes the signal from the programmer.

  11. #11
    Master murkeywaters's Avatar
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    Quote Originally Posted by blackal View Post
    It still only en-passes the signal from the programmer.
    So when mine plays up, I switch the programmer to off = no signals being sent, thermostat in frost mode = no signal being sent but the heating still runs at full blast, this is because this diverter valve gets stuck and keeps asking the boiler for heat, I have repaired mine about 3 times now over several years and it works every time.

    Combi being fitted after Christmas so i'll be glad to rip all this old antiquated system out!

  12. #12
    Master blackal's Avatar
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    Quote Originally Posted by murkeywaters View Post
    So when mine plays up, I switch the programmer to off = no signals being sent, thermostat in frost mode = no signal being sent but the heating still runs at full blast, this is because this diverter valve gets stuck and keeps asking the boiler for heat, I have repaired mine about 3 times now over several years and it works every time.

    Combi being fitted after Christmas so i'll be glad to rip all this old antiquated system out!

    Mmmmm....

    - - - Updated - - -

  13. #13
    Master
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    OP

    Switch your programmer to off for the heating and hot water, turn down your thermostat to 5c and let us know what happens.

  14. #14
    Quote Originally Posted by CaptainSlow View Post
    OP

    Switch your programmer to off for the heating and hot water, turn down your thermostat to 5c and let us know what happens.
    Will do. For now itís working again as I turned the mains off and on. When it gets stuck again Iíll do as you suggest.
    Many thanks

  15. #15
    Master blackal's Avatar
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    A quick scan of the S-Plan or Y-plan indicates that the solenoid valve gets a supply to operate the solenoid, and a supply to en-pass to the boiler to switch on.

    The en-pass signal comes from the boiler, to me

  16. #16
    Craftsman
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    Has said most of the problems are usually caused with the port valve sticking in one position.
    Usually if it is this it usually omits a buzzing sound.
    Usually when your heating is on all the time the port valve is jammed in one position, sending power to the boiler (turning it on)

  17. #17
    Master yumma's Avatar
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    My three way valve went wrong/jammed recently, cost £140 for a good plumber to replace and the heating is all hunky dory again. Good luck.

  18. #18
    Master
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    Exactly the same problem here about 4-5 years ago and it was the valve sticking also

  19. #19
    Master Kirk280's Avatar
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    Just open the windows a bit.

    HTH

  20. #20
    Grand Master
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    Quote Originally Posted by Kirk280 View Post
    Just open the windows a bit.

    HTH
    Or sit around in shorts pretending youíre on holiday

    Itís better than the central heating failing in winter!

  21. #21
    Master blackal's Avatar
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    Looking at all the people who have responded who experienced a stuck motor valve - Surely your heating (or hot water) were still being Ďdemandedí by the programmer? i.e - if the programmer was set to Ďoffí on both CH and HW - then there was no boiler demand? Is what you are describing - the boiler running full bore while the timer demands either HW or CH?

    In that above scenario - yes, freeing up the valve/switch, will in all probability - solve the problem.

    From what the OP says - his heating continues to run with the programmer off? That does seem to indicate that the programmer is sending a ďRunĒ signal to the motor valve and on to the boiler, also energising the solenoid to move the motor valve.

    If you have a look at the S-plan and Y-plan, you see that the motor valve being in a Ďdemand positioní is not enough to fire up the boiler.

    https://www.flameport.com/electric/c...ing_Y_plan.cs4

    https://www.flameport.com/electric/c...ing_S_plan.cs4

    The programmer must:
    1) Feed through the Thermostat, and motor valve position switch - to energise the boiler
    2) Energise the motor valve - to move to an open position, and make the position switch above.

    Both the above signals must be present to fire up the boiler.

    (unless there are systems that are wired up weird)

  22. #22
    Craftsman
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    They are really easy to change, providing you have good access. Pull the fuse for the system, trace the wires back to the junction box, ensure no current to the terminals, make a note of the wiring, remove wires, and the switch will be held on by 4 screws underneath. Unscrew the switch and swap out with the new one, reconnect the wires and off you go. I had a heating engineer out first time mine went and watched what he did. There is no need to drain the system down as the seal is in the "T" piece.
    If you need it done asap and feel competent enough have a go, your local plumbing supplier will have them on the shelf.

  23. #23
    Master blackal's Avatar
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    Quote Originally Posted by Beanie View Post
    They are really easy to change, providing you have good access. Pull the fuse for the system, trace the wires back to the junction box, ensure no current to the terminals, make a note of the wiring, remove wires, and the switch will be held on by 4 screws underneath. Unscrew the switch and swap out with the new one, reconnect the wires and off you go. I had a heating engineer out first time mine went and watched what he did. There is no need to drain the system down as the seal is in the "T" piece.
    If you need it done asap and feel competent enough have a go, your local plumbing supplier will have them on the shelf.
    Youíre right - you can investigate a Ďstuck valveí and hopefully sort it without opening up the water circuit. Certainly as plan A. I got severely put down by a Ďplumberí on another forum, who insisted that you ďchange out the entire valve! Iíve been in the trade for XX years!Ē I guess thatís how they make money!

    It should by probability - be just the switch U/S or simply loose. An easy fix. But- the valve itself may be the culprit. (It might not be stroking fully)

  24. #24
    Craftsman
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    The valves also pass the signal on and can be dodgy out of the box.
    I did some work for a boiler manufacturer a while back and we spent days arguing back an forth about a bug in the system very similar to the opís which turned out to be the valve outputting an out of spec signal.
    Weirdly when we moved into our new place a month ago we had odd things happening with our heating, turned out to be, yep, dodgy valve.



    Sent from my iPhone using Tapatalk

  25. #25
    Master IAmATeaf's Avatar
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    Iíd go with faulty programmer or faulty boiler circuit board.

    Iíve got a similar system to the OP and Iíve have on occasions when in the loft manually moved both diverter valves when in the loft just to exercise them and my boiler has never fired up as a result.

  26. #26
    Grand Master oldoakknives's Avatar
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    So this guy is free falling to the ground and as he's falling he sees a chap hurtling up towards him.

    Seeing his chance he calls out, "Hey do you know anything about parachutes?"













    "No...." the chap shouts back "...do you know anything about gas boilers?"

    Start the car.............
    Courage is being scared to death but saddling up anyway.

  27. #27
    After it not working on Thursday and then again on Friday itís been fine since.I've got a plumber coming at 9 am tomorrow but not sure what he will be able to diagnose if itís all working.
    Last edited by awright101; 24th November 2019 at 18:38.

  28. #28
    In the S plan even if the programmer isn't calling for heat the boiler could still fire due to a faulty motorised valve. The valve has a permanent feed to it which is completely independent of the programmer. Its this feed that connects to the boiler switch live when the valve motor is activated.

  29. #29
    Master blackal's Avatar
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    Quote Originally Posted by scottbombedout View Post
    In the S plan even if the programmer isn't calling for heat the boiler could still fire due to a faulty motorised valve. The valve has a permanent feed to it which is completely independent of the programmer. Its this feed that connects to the boiler switch live when the valve motor is activated.
    Just checked - yes, it could.

  30. #30
    Quote Originally Posted by murkeywaters View Post
    Mine was doing the same and is a tank fed system, it was a diverter valve getting stuck, looks like a rectangular metal box on the pipe work near the boiler.

    If you have a combi then something else I imagine?

    THIS - I had the same

  31. #31
    Administrator swanbourne's Avatar
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    Mine did the same, it was the motorised valve. British Gas installed a new system but left the old valve in place.

    Eddie
    Whole chunks of my life come under the heading "it seemed like a good idea at the time".

  32. #32
    Craftsman
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    I had this a couple of times, it was the electronic section of the motorised valve jamming continually sending the boiler a Ďheat requiredí signal, the mechanical part was fine and so I only changed the motor part, 10-15 minute job.

  33. #33
    Master IAmATeaf's Avatar
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    Just read up on a plan and didnít know that the motorised valve(s) actually fire the boiler. So am I allowed to now fall into the itís the motorised valve camp

  34. #34
    Craftsman
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    The valve is stuck. I replaced mine a few weeks ago, which is about the 4th time over 25 years. It has nothing to do with the programmer, once its stuck the cog wheel in the mechanical bit sticks, so even no power it won't return to the closed position. Squirting WD40 through the slot, won't make much difference as the bit that normally breaks is near the top of the box. You can buy the motorised bit separately from Screw fix, just make sure you get the right one, some are two way valves, some are three. It takes about 20 mins to replace the motorised head, the head should be around £70. You shouldn't need the whole valve. But to check, take off the head, its only held on with a couple of screws, then if you can move the actual valve stem then the head is broken. If the actual valve on the bottom is stuck, then you will need the whole thing, but that doesn't happen often. To change the head, you don't need to isolate any water etc, just the electrics and then just wire it up the same as the one you take off.

  35. #35
    Craftsman
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    Quote Originally Posted by IAmATeaf View Post
    Just read up on a plan and didnít know that the motorised valve(s) actually fire the boiler. So am I allowed to now fall into the itís the motorised valve camp
    Sssssh(sucks teeth as per quote time) ... yes ok, takes a good guy to admit he was mistaken. (Never wrong)

  36. #36
    Craftsman
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    Last couple I done were actually cheaper to buy complete than just the electronic component, I just take a picture of it hopefully showing manufacturer name and any part number and plod off to the plumbers merchants, I do get a better deal there than screwfix and better advice too.

  37. #37
    Quote Originally Posted by casbar View Post
    The valve is stuck. I replaced mine a few weeks ago, which is about the 4th time over 25 years. It has nothing to do with the programmer, once its stuck the cog wheel in the mechanical bit sticks, so even no power it won't return to the closed position. Squirting WD40 through the slot, won't make much difference as the bit that normally breaks is near the top of the box. You can buy the motorised bit separately from Screw fix, just make sure you get the right one, some are two way valves, some are three. It takes about 20 mins to replace the motorised head, the head should be around £70. You shouldn't need the whole valve. But to check, take off the head, its only held on with a couple of screws, then if you can move the actual valve stem then the head is broken. If the actual valve on the bottom is stuck, then you will need the whole thing, but that doesn't happen often. To change the head, you don't need to isolate any water etc, just the electrics and then just wire it up the same as the one you take off.
    Thanks. The plumber came this morning and the value was very stiff and felt that would be the culprit. He said there is a spring in the box turn turn the heat to water etc but it does not have that much strength. He said he could try and loosen it but it will stiffen up again. Heís coming back on Thursday to replace the valve and head as together they were not much more.

    Thanks for all the advice
    Andy

  38. #38
    Master blackal's Avatar
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    Apologies for the bum-steer...............

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