Central Heating Programmers keep breaking

[nicck]

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.

 

[Aragorn84]

Your saying you can remove the programmer and the boiler stays on?

That sounds more like the zone valves are sticking?

Typically the programmer opens the zone valves, then the zone valves have a microswitch which engages the boiler via a seperate circuit.

If the zone valve were to stick open, the boiler would continue to run.

 

[nicck]

Typically the programmer opens the zone valves, then the zone valves have a microswitch which engages the boiler via a seperate circuit.

If the zone valve were to stick open, the boiler would continue to run.

If this is the case, could it be causing the programmer to fail? And then why did it work as normal for a few months after the programmer was replaced?

 

[45yearsagasman]

In what way has the programmer "failed"? If the system continues to run after the programmer has been removed, then its a fault that has already been mentioned.

 

[nicck]

I will check the zone valves and report back.

 

[hazetimesfive]

did you replace back plate as well.

 

[nicck]

did you replace back plate as well.

No backplate was not replaced, old one was examined carefully and seemed to make right connections. Contacts were tested to be wired correctly.

 

[hazetimesfive]

always replace the backplate.

 

[nicck]

always replace the backplate.

Any particular reason or just good practice?

 

[hazetimesfive]

dirty contacts, bent contacts, fizzle pop.

arcing would never be very good for any kind of leccy gear.

its good practise and I've had to go back and change back plates on replacement programmers, money out of my pocket.

 

[nicck]

Hi All,

A big thanks to everyone who helped.

Problem was on the automated valves.

You can see on the pictures;
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.

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• nicck
• 18 Feb 2013
• 1

Untitled

• nicck
• 18 Feb 2013
• 1

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