Cannot turn off Central heating

[Christoph88]

Hi, I have a Worcester greenstar Ri on a Y plan system with hot water cylinder. Problem I'm having is heating won't switch off once on, it ignores the room stat and programme and stays on. I've tried; new 3port motorised valve, new programmer/timer and also new room stat. I've also disconnected the frost stat, no change. Had an electrician out he seemed to want to blame the cylinder hot water thermostat.
Any help on this would be very much appreciated?

 

[Knappers]

Its unlikely to be a fault with the boiler but sounds like a job for a heating engineer.

 

[Christoph88]

Its unlikely to be a fault with the boiler but sounds like a job for a heating engineer.

Hi and thanks for replying, I've had 2 plumbers and 2 electricians out (3 if you count the fact the last visit there was 2 guys). And I'm still stuck with the fault.
The last guys tested the cylinder stat and said it was faulty and likely causing the fault, said they'd be back to fix last week but haven't. I'm a bit frustrated with it. Can a cylinder stat send a faulty signal keeping CH from turning off?

 

[Knappers]

In some circumstances yes

 

[John.g]

Think I read somewhere that the diverter (normal) 60V de magnetising voltage can, in some cases keep the boiler running and a capacitor should be installed somewhere or other at the boiler. (probably the switched live)

With the cylinderstat and roomstat at minimum, check the diverter valve in the HW position (port B ?) then turn up the roomstat and see does the diverter move across to CH (port A), turn roostat down again and see if the diverter remains in the CH position which I think it should (but with boiler off) turn up the cylinderstat and turn down the roomstat and the valve should move back to HW (port B) (with boiler on) turn up roomstat and valve should move to mid position.

If you kill the power to the boiler while running when it shouldn't and then restore it does it restart?.

If its only happening on CH then could be this voltage and apparently some diverter valves give a higher voltage than others.

"I have solved the problem now. It turns out that honeywell and similar 3 port valves have a residual voltage left when the heating is satisfied. Talking to Biasi the boiler manufacturers, they told me this is becoming a common problem which can be solved in one of two ways. Replace the honeywell valve for a Drayton as the residual voltage is less than 20v on that one or put a 0.47 microfarad capacitor across the switch live and neutral to take the power away."

 

[Murdoch]

Doesn't sound like any of them knew how to fault find central heating. ..............

 

[Christoph88]

Think I read somewhere that the diverter (normal) 60V de magnetising voltage can, in some cases keep the boiler running and a capacitor should be installed somewhere or other at the boiler. (probably the switched live)

With the cylinderstat and roomstat at minimum, check the diverter valve in the HW position (port B ?) then turn up the roomstat and see does the diverter move across to CH (port A), turn roostat down again and see if the diverter remains in the CH position which I think it should (but with boiler off) turn up the cylinderstat and turn down the roomstat and the valve should move back to HW (port B) (with boiler on) turn up roomstat and valve should move to mid position.

If you kill the power to the boiler while running when it shouldn't and then restore it does it restart?.

If its only happening on CH then could be this voltage and apparently some diverter valves give a higher voltage than others.

"I have solved the problem now. It turns out that honeywell and similar 3 port valves have a residual voltage left when the heating is satisfied. Talking to Biasi the boiler manufacturers, they told me this is becoming a common problem which can be solved in one of two ways. Replace the honeywell valve for a Drayton as the residual voltage is less than 20v on that one or put a 0.47 microfarad capacitor across the switch live and neutral to take the power away."

Thanks for the in depth reply, the system is quite old, and has worked OK for the past few years. Only recently this fault has happened.
If the valve is in position B and you turn the room stat up it'll move all the way over to A and CH comes on, turn room stat down it stays in position and boiler continues to burn (although every now and again it'll cut off then relight, then cut off and relight, like it wants to power down but then it gets a signal to re fire over and over). If you turn boiler off and on again, it'll try and relight even with the room stat still off. The only way to turn it off is to cut supply to the whole system, port valve will move back and the faulty demand goes away.
I've put 3 different motorised heads on 2 honeywell and one aftermarket.

It's confusing as it worked OK for years?

 

[John.g]

Is the boiler shutting down normally if on HW only??
If so then on CH only and roomstat turned down with boiler still running (wrongly) just remove the switched live and see if the boiler shuts down, if it doesn't then the fault is within the boiler.
If the boiler is behaving normally on HW only (turning the stat up/down) then difficult to see a cylinderstat problem.

 

[Murdoch]

Is the boiler shutting down normally if on HW only??
If so then on CH only and roomstat turned down with boiler still running (wrongly) just remove the switched live and see if the boiler shuts down, if it doesn't then the fault is within the boiler.
If the boiler is behaving normally on HW only (turning the stat up/down) then difficult to see a cylinderstat problem.

are you sure giving such instructions to unknown DIYers is such a good idea? I don't

 

[Christoph88]

Is the boiler shutting down normally if on HW only??
If so then on CH only and roomstat turned down with boiler still running (wrongly) just remove the switched live and see if the boiler shuts down, if it doesn't then the fault is within the boiler.
If the boiler is behaving normally on HW only (turning the stat up/down) then difficult to see a cylinderstat problem.

Switched live is orange wire on the motorised valve (I believe looking at plans) , if I remove orange wire whilst running CH goes off straight away.

 

[John.g]

All I can say is if the boiler continues to run on CH with the roomstat turned down then either some wiring fault or the voltage supplied via the resistor(s) to the orange wire is sufficient to keep the boiler firing.

 

[Christoph88]

All I can say is if the boiler continues to run on CH with the roomstat turned down then either some wiring fault or the voltage supplied via the resistor(s) to the orange wire is sufficient to keep the boiler firing.

Hi again, I switched out the honeywell for a Drayton valve to reduce residual voltage...same fault. But!! It works fine with the motorised head is off the valve, I noticed the 3 port diverter doesn't turn all the way, its seized on the last little turn meaning the motorised head isn't able to complete it's full rotation.
So now I need to change that port valve..do I need to drain the system? Or can I isolate it from the pump valve?

 

[John.g]

Good to hear you have tracked it down, thought you had changed the whole valve previously but obviously the actuator, presume you can't free up the valve by opening/closing it to its limits?, you may have to drain down the system to change the valve except its high up in a airing press where a partial drain down will suffice.

 

[Christoph88]

Good to hear you have tracked it down, thought you had changed the whole valve previously but obviously the actuator, presume you can't free up the valve by opening/closing it to its limits?, you may have to drain down the system to change the valve except its high up in a airing press where a partial drain down will suffice.

Cheers for your help. I'm just refilling the small header tank now, I just blocked off the float and drained that. Changed to a brand new drayton valve. Fingers crossed this fixes it. Tried grips on the old port but it was stuck solid once it got near to the end of travel.

I'll bleed rads first. Wish me luck haha.

 

[Christoph88]

Good to hear you have tracked it down, thought you had changed the whole valve previously but obviously the actuator, presume you can't free up the valve by opening/closing it to its limits?, you may have to drain down the system to change the valve except its high up in a airing press where a partial drain down will suffice.

Well the original fault has gone, but there's an airlock in the system now, and boiler cuts out rather quickly with some loud knocking gurgling noises air lock...I was afraid of this. Any further tips?

 

[Gasmk1]

when you refilled did you have the valve open manually, just turn boiler right down and keep turning the pump on and off to move air

 

[Christoph88]

when you refilled did you have the valve open manually, just turn boiler right down and keep turning the pump on and off to move air

Thank you, I think so but the valve was stuck so it wouldn't go all the way over.
I'll try this. Thanks

 

[John.g]

Hope you got rid of the air and everything is back to normal, you did very well to test with the actuator removed from the valve because despite not going fully over to CH only, once the white wire which feeds the orange wire falls to zero volts via either a satisfied roomstat or the CH programmed off then the boiler should still have shut down IMO.

 

[Christoph88]

Hope you got rid of the air and everything is back to normal, you did very well to test with the actuator removed from the valve because despite not going fully over to CH only, once the white wire which feeds the orange wire falls to zero volts via either a satisfied roomstat or the CH programmed off then the boiler should still have shut down IMO.

It was a strange one indeed, actuator worked great off the valve, once on the valve it stuck on ch, valve was rusted inside most likely 30years old.
But it's all fixed now. New 3 port diverter, new drayton actuator, all the system bled...I had to bleed the boiler, then the bleed valve in the attic, then bleed all the rads from the bottom valve into a bucket. Only then did everything work as it should...phew.

Thanks to everyone who chimed in on this I've been puzzling over it for the best part of 6months.