How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Andrew Smith Your Own Question
Andrew Smith
Andrew Smith, Plumber
Category: Plumbing
Satisfied Customers: 3767
Experience:  City and Guilds qualified plumber
Type Your Plumbing Question Here...
Andrew Smith is online now

My central heating system won't turn off. I've tried

This answer was rated:

My central heating system won't turn off. I've tried turning the thermostat down and switching off at the timer (Honeywell st7100) but even when that says it's off - it's still pumping and it seems, on full power.
The only way to switch it off is at the mains which switches off the whole system and shuts down the boiler - an old (not combi) boiler (potterton Promax HE).
It appears to have two valves: a myson compact which looks like the heating one and a blue one that has an AB switch And the writing 'valve actuator CODL BGMVSP-2'
If I turn it on at the mains again it boots up immediately and fires up the boiler. It's difficult to tell if the hot water is also coming on and sticking on.
Hope you can help!
You are looking in the right place.Is it the hot water or heating that is staying on? This is the valve that will be stuck.If you turn the power off to the heating, check the levers on the valves and see if they are still slack. If one is slack then it means it is still stuck open - this will keep the pump and boiler running.
Customer: replied 2 years ago.
Thanks for this.Hard to tell but I think it's just the central heating as a) there seems to be a change when I override the controller box to turn the water on and b) the central heating override no longer seems to work - it's permanently on the off setting but obviously permanently onHard to tell re valves:The myson compact doesn't have a lever but has a switch with three settings on it. These seem to change the flow - none of them turn it off but the audible tone is higher/ mid/lower depending on which setting the switch is on. It's been on the highest and doesn't click through independently at any point.The blue valve has an A/B indicator on the side and a black lever on the front. It doesn't feel slack as such and when I turn it when the system is on it simply slides slowly back into the A position, it's default. It does change from a to b when I switch the water though - so I guess clearly the hot water system. This seems to happen smoothly going back to a when water turned off at box.So, looks like heating rather that water. Could it be the digital controller box?
Customer: replied 2 years ago.
Ah- one more thing. There is also a Honeywell box at a similar height to the blue water valve box that may be the valve for the heating. The switch goes from one setting to 'man' and doesn't change by itself no matter if on at the mains or any other setting. I can change it but it seems to do nothing.
I think you have found it.The valve that is stuck is the problem, you will find that the microswitch inside is stuck 'made' keeping your pump and boiler running.You should change the head, but if the pin underneath does not move then you may have to change the body also.
Customer: replied 2 years ago.
Thanks. I'm not clear on what the head / body means? Also, is this something I can do myself, removing the casing when turned off at the wall? Finally, are replacements something I can find in most plumbers merchants? Thanks, Matt
The silver Honeywell box is held on with 2 screws once you get the cover off. It is a sealed box so you do not need to drain the heating.If this does not cure it then you will need to drain the heating and swap the body.
Andrew Smith and other Plumbing Specialists are ready to help you
Customer: replied 2 years ago.
Spot on, thanks. Have replaced it and now all working correctly. :-)