Heating will not 'switch off'

[tony1205]

Dear Forum

I am a newbie on this site - I am not Gas Safe qualified - but am retired, with lots of time but not money! I can find my way around a wiring diagram and am proficient with a multimeter. I'm prepared to have a go wherever I can, if I'm not breaking the law!

CH system has been working well, until the last couple of days, when we have been waking up to a roasting hot house. We have an Concorde WRS boiler, Randall 4033 programmer, a Honeywell 4073a mid position valve and a Honeywell L641 cylinder stat.

I initially thought that the frost stat/pipe stat had failed, but am not so sure now. It appears that if I increase the setting of any of the stats(including the cylinder stat), the boiler fires up. However, when the appropriate stat setting is lowered, the boiler does not cut out and continues to fire( regardless of the programmer setting) The only way to stop it firing, is to switch off the mains power to the system.I re-energise mains power to system and boiler remains off.Then when the system again calls for heat, the cycle repeats itself.

I have not got a problem with calling in an expert if I need to, but I'm prepared to have a go myself, if I can. Does this sound like a problem with the mid position valve to you guys?

I have had a look at the 4073a and I think it's of the older variety, which means I cannot replace the actuator head without draining down the system. If that's the case, it will be a job for a plumber in my opinion. Am I barking up the wrong tree with my assumptions?

All or any advice, greatly appreciated

 

[AaronC]

Dear Forum

I am a newbie on this site - I am not Gas Safe qualified - but am retired, with lots of time but not money! I can find my way around a wiring diagram and am proficient with a multimeter. I'm prepared to have a go wherever I can, if I'm not breaking the law!

CH system has been working well, until the last couple of days, when we have been waking up to a roasting hot house. We have an Concorde WRS boiler, Randall 4033 programmer, a Honeywell 4073a mid position valve and a Honeywell L641 cylinder stat.

I initially thought that the frost stat/pipe stat had failed, but am not so sure now. It appears that if I increase the setting of any of the stats(including the cylinder stat), the boiler fires up. However, when the appropriate stat setting is lowered, the boiler does not cut out and continues to fire( regardless of the programmer setting) The only way to stop it firing, is to switch off the mains power to the system.I re-energise mains power to system and boiler remains off.Then when the system again calls for heat, the cycle repeats itself.

I have not got a problem with calling in an expert if I need to, but I'm prepared to have a go myself, if I can. Does this sound like a problem with the mid position valve to you guys?

I have had a look at the 4073a and I think it's of the older variety, which means I cannot replace the actuator head without draining down the system. If that's the case, it will be a job for a plumber in my opinion. Am I barking up the wrong tree with my assumptions?

All or any advice, greatly appreciated

Sounds to me as if the mid-position valve is faulty

 

[southcoastboile]

no ur probably right in it being the 3 port, not sure what colour wires you have there but normaly you will have earth neutral live then a white and a grey, grey does hw and white htg, if you have nothing on white or grey when programmer is off and 240 on orange then actuator has likely gone, if not then there is probably a fault with other ext controlls i would definitly recomend you get a qualified engineer to fit the part.

 

[Simon F]

test the orange wire it should only be live when programmer and room stat call for heat

 

[tony1205]

Gents,

Many thanks for the rapid replies! I think I will take your advice and contact a local expert. It makes me feel a little better to know it is probably the valve that has gone.

 

[quality]

Please post your location and a respected chap from the forum may be able to help

 

[diamondgas]

If I may add agreement with the others here tony. the silver head (actuator) sounds like it's duff! You can change them but it depends on the age to be honest and isn't to hard a job to undertake if you know how to use a screwdriver and are capable of isolating electricity and swapping wiring like for like ...... IMHO

 

[tony1205]

diamondgas,

Looking at the valve with the cover off, I'm certain it's the type of valve where you cannot remove the actuator, without draining down the system. I'm quite prepared to have a go if this was not the case. But if it means a drain down and pipe alterations, I think I'll be digging a hole for myself! Not good, approaching Xmas!

 

[diamondgas]

diamondgas,

Looking at the valve with the cover off, I'm certain it's the type of valve where you cannot remove the actuator, without draining down the system. I'm quite prepared to have a go if this was not the case. But if it means a drain down and pipe alterations, I think I'll be digging a hole for myself! Not good, approaching Xmas!

Very true 🙂 The removable actuator has two diagonally apposed raised screw heads with a curved recess cut out of the actuator motor base plate. To be honest a new valve is only a cupl of quid more than the head but installing is a darn sight less troublesome 🙂

As mentioned, post your request on the site and you may be fortunate to get a PM from one of us 🙂