Thermocouple with interpreter stat :(

[gassafe]

Gas fire
The fault was a pilot not staying lit so I ordered a pilot assembly kit. Fitted it okay, but when releasing the button pilot cuts off immediately

i disconnected overheat interrupter on thermostat & bridged with piece of wire, pilot stays lit & main burner works!

I put multimeter on overheat connectors & its closed circuit so now I'm confused! The overheat stat is not faulty it seems, but the pilot will not stay lit with it connected! I'm hoping a new overheat will fix it, but I'm wondering if it will now!?

New thermo gave 20.1 volts on multimeter when hot, the interrupter overheat said something like 0.8 & is closed circuit always.

Any advice appreciated...?

Test wire removed by the way, so all is safe

 

[firemant]

What fire is it, or is it a stove? Is there a microswitch (or 2)?

 

[mountainman]

I doubt you'd get 20 odd volts from a thermocouple, I suspect your test method is faulty.
If I remember correctly a good TC gives about 39mv and if you have more than minimal resistance on the interrupter then the valve won't hold open.
Replace the TC first.

 

[gassafe]

Thermo has been replaced already.
My testing method may be wrong, I have never understood how people talk about testing a thermo with multimeter I heated the tip with pilot, and then took measurement from tip to magnet end. I think I meant to say 20 on resistance.

The new thermo worked fine with my test wire wrapped around the interpreter connections! Does this mean it would be interpreter & stat?

The interpreter is just a basic overheat stat on base of flue for flue spillage! It's a basic gas type stove with coals, cast iron box! No microswitches!

 

[Billy Bob Bob]

Thermo has been replaced already.
My testing method may be wrong, I have never understood how people talk about testing a thermo with multimeter I heated the tip with pilot, and then took measurement from tip to magnet end. I think I meant to say 20 on resistance.

The new thermo worked fine with my test wire wrapped around the interpreter connections! Does this mean it would be interpreter & stat?

The interpreter is just a basic overheat stat on base of flue for flue spillage! It's a basic gas type stove with coals, cast iron box! No microswitches!

think about this logically,you have ruled out the TC,the interrupter is just a piece of wire,test both ends if you get continuity its fine,if not its faulty,some OH stats are open circuit,some are closed circuit,did you try just bridging the stat on its own? if its a TTB style sensor in the flue is there spillage taking place?

 

[lame plumber]

does it interprept french or german, could be useful if you go on holiday.

 

[mountainman]

Set your multimeter on the millivolts range and test the output from the TC, about 39 is good if my memory serves.

Set your multimeter to low resistance and check the interrupter.
Any resistance should be virtually zero as anything higher will affect the final voltage delivered to the valve.

Your logic of looping out the interrupter is sound but unless you establish that the thermocouple is sound then a tiny voltage loss through the interrupter could cause your failure.

Ten minutes face to face and I could have shown you all you would ever need to know about thermoelectric valves.

 

[gassafe]

It's like this

 

[gassafe]

I bridged it across those pins, and it worked okay, also worked when attached to the overheat stat ( which is a regular boiler looking one, closed circuit always). I had 0.8 resistance through leads/stat, and it bleeps on multimeter to mean a circuit!

Your guidance on thermos would have been appreciated today mountain man! I am now thinking if the overheat stat is closed circuit & seems to be working then maybe new thermo not giving a good enough reading to hold gas valve open! Is this common? But then by puttin the wire across terminals & it works makes me think the oh stat & leads are at fault or creating too much resistance!

Its not cutting out on spillage, its not staying lit at all to activate the stat!

 

[lame plumber]

you have proved the thermocouple is fine by bridging the interuptor, so its either a continuity fault in the wiring of the overheat stat thats failed

 

[gassafe]

you have proved the thermocouple is fine by bridging the interuptor, so its either a continuity fault in the wiring of the overheat stat thats failed

Thanks, that what I was hoping, I just thought that it being closed circuit & passing multimeter tests would normally mean its okay, so it confused me! I shall replace & update!