Central Heating Programmers keep breaking

[nick]

I have an old floor standing gas boiler CH system with hot water storage tank.

This has worked just fine for few years. The only things needing replaced were the HW/CH valves that control the water flow.

Problem
The control unit
Horstmann Centaurplus C27 Heating Programmer
broke about a year ago so I replaced it. The replacement only lasted about nine months, I figured I had a duff unit and replaced it again. The new one has gone after about three months.

They all broke in the same way. Unit appearers to be working, all timing and lights work as normal however the boiler turns on and stays on no matter what the unit is set to.

The unit appears to suppress the boiler operation. If it is removed completely the boiler stays on for both HW & CH.

There is a fused switch that supplies the power to the unit backplate and I can turn this off to turn off the boiler.

Has anyone experienced this before? Or got any ideas. I don't know if it is a system of the CH system or there is a problem with the house electrics.

 

[JohnKay]

Hi
Am I right that the boiler stays on even if you remove the programmer from the backplate ?
If this is the case, then the most likely problem is a motorised valve.

 

[nick]

Hi
Am I right that the boiler stays on even if you remove the programmer from the backplate ?
If this is the case, then the most likely problem is a motorised valve.

Yes the boiler stays on even if I remove the programmer from the backplate. However only if the fused switch that supplies the power to the backplate is also on.

I understand that the motorised valves could stick open and if they have a micro switch they could override the controll unit, but can tehy cause it to fail?
Remember that when I replaced the programmer it worked as normal for several months before the problem reappeared. So I don't understand how it could be caused by a motorised valve. Open to persuasion if you can explain it.

 

[JohnKay]

The programmer operates the valve via the thermostats. The boiler and pump are switched by the valves. In the situation you describe, the valve is defective.

How can the programmer be keeping the boiler running if it's not even fitted ?

 

[nick]

The programmer operates the valve via the thermostats. The boiler and pump are switched by the valves. In the situation you describe, the valve is defective.

How can the programmer be keeping the boiler running if it's not even fitted ?

Good question. I will check the valves and see.

 

[JohnKay]

Let's know exactly what valves you have nick, and we can sort it out.

 

[nick]

Hi All,

A big thanks to everyone who helped.

Problem was on the automated valves.

One of them was corroded, this was caused by a minuscule leak.
the other had plastic failure, the posts which held the return springs have bot broken off so the valve was jammed open with the microswitch activated.

 

[JohnKay]

Thank you for the feedback nick, good to know it's all sorted.