Good afternoon, My Central heating has decided to stay on even when switched off. I have a 20 year old Baxi Bermuda back boiler with a Horstmann mechanical timer/controller. I turned the hot water off and this seems to work, but not the CH, the rads are on all the time. I turned down the stat on the front of the boiler which does help a bit. Any ideas? The boiler hasn't been serviced for over a year as I'm changing the system soon. Thanks, WM
Sounds like a faulty clock, which if you are upgrading your system will require replacing anyway.
Zone valve actuator sticking, sending a call for heat to the boiler even when the roomstat/timer isn't calling for heat.
Owain
Is it gravity HW and pumped CH, or fully pumped? If fully pumped, can you identify which 'Plan' it is, by referring to
That could certainly be the case if it's an S-Plan system. Being 20 years old, I'm not sure how likely that is though.
It is gravity with pumped CH.
The way in which such systems usually work is as follows:
If your CH is on all the time regardless, *something* is telling the boiler and pump to run. Most likely the CH contacts in the programmer have become welded in the ON position.
But I'm puzzled by your ealier statement saying "I turned the hot water off and this seems to work". Whenever the CH is on, the HW is *automatically* n - unless you've got a C-Plan system (see the Honeywell reference, above) involving a motorised valve and a tank stat. Would you care to clarify?
I probably made a mistake there. What I meant was, that I turned off both HW and CH at the controller and after filling the sink a couple of times for doing the dishes, the water wasn't getting as hot as usual. There are 2 motorised valves.
OK - we need to back-track a bit. If there are 2 motorised valves, it's very unlikely to be a gravity HW system - in the sense I mean, anyway. Maybe you simply meant that the HW gets to the taps by gravity - with a header tank feeding the hot cylinder?
That wasn't what I meant. I was talking about gravity (convection) circulation in the primary circuit from the boiler to the indirect coil in the hot water cylinder. I suspect that this is acually a pumped circuit, along with the central heating?
Any chance of uploading one or two pictures of the valves, and related pipework to somewhere on the net - and posting the URL here?
Have another look at the Honeywell reference which I gave, and see whether your system looks like an S-Plan.
Fixed it, I think. Don't know the science but.. I played around with the Manual-Auto lever on the Sunvic actuator and resetting all the controls/stats to what they were. I also switched it off and on a few times and turning the stat up and down and now it works again. It may be a dodgy valve or actuator giving me an early warning. These will be changed soon anyway. So thanks for all your input.
The science is that the programmer and stat open the valve, and some auxiliary contacts in the valve actuator switch on the boiler and pump once the valve opens. So if the valve sticks open, the boiler continues to run - even when off at the programmer and/or room stat. [This can be seen if you study the S-Plan wiring diagram in the Honeywell reference which I gave earlier].
Operating the manual lever, and exercising the valve a few times, will have unstuck it.
In message , wattie writes
There's a good chance you just freed a sticky actuator.
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