Thorn Apollo Thermocouple

[Daveuk]

I wonder if somebody can give me some advice, I've been lumbered, by my wife, with finding out why her sister's Thorn Apollo Boiler won't work. Basically the pilot won't stay lit, which in my experience, strictly amateur of course, usually signals a thermocouple problem. Sure enough the thermocouple is absolutely knackered, but it is one of those strange ones with I think what is an interruptor in the line. I've purchased a new thermocouple, and fitted it but still no go, what I would like to know is, if what I take to be is a thermostat, which is connected to the terminals on the thermocouple actually fails, will that prevent the thermocouple doing its job, hence pilot light not staying lit.

The said boiler is quite old and I have advised my sister in law that really it should be replaced, but she can't do that for a few months yet, so I would like to help her out.

I would appreciate any help which may be given.
Regads
Dave

 

[ollski]

Yes if the interruptor has gone the circuit will be broken so the pilot valve will not stay open. You have ruled out the more likely fault that the pilot is dirty and so the flame is not reaching the thermocouple?

 

[Daveuk]

Ollski, thanks for that, is the interruptor the small black object which is attached to the spade terminals on the thermocouple and which I take it is a form of thermostat?.

Yes I have ensured that the thermocouple is well immersed in the flame, I was wondering if as a form of test I might be able to bridge the two terminals on the thermocouple with fuse wire thereby completing the circuit and proving whether or not the thermostat has gone. Is that feasible?, if it is and the pilot then stays on, I would obviously not leave it operating in that condition for safety's sake.

Thanks again
Regards
Dave

 

[Gees]

I had a gemini boiler that used the same thermocouple and yes you can just short out the link to do the tests. but for safety reasons you should not leave the link in position. Your problem may lie in the elctromagnet that holds the gas vave open when activated by the current from the thermocouple. I once had the wire come off within this item and needed a new gas valve...

 

[netaheat]

Dreadful things, Thorn Apollo's...
On a Thorn Apollo the interruptor should be brdiged by the overheat thermostat. During normal conditions, the overheat stat should be short circuit; check it with a meter, the stat opens on rise of temp.
There may be a manual reset on the overheat stat.
Hence, if the boiler overheats (say due to the control stat going short circuit) the flame failure device is opened and this cuts out the pilot.
Yes, you can bridge the interruptor but only to prove that the overheat stat is open circuit.
Bridge the interruptor and try to light the pilot, if the pilot flame holds, the overheat stat is o/c.
Next you must find out why the overheat stat is o/c.