Gas oven thermostat

[Reentrant]

Our gas-oven thermostat has failed again - they only seem to last about

5 years. It's one like this: it is relatively straightforward - I've done it twice now - but I have a couple of queries.

1) Although it's called a thermostat in the service manual, the bulb sits directly in the gas flame so presumably its main job is to confirm the pilot-light is lit. How does it regulate the oven temperature if it's in the burner (or is it not literally a thermostat?)

2) The connecting copper tube is very thin. Is it a capilliary tube, and pressure in the bulb opens the gas control valve, or is it solid and just conducts heat to a sensor in the control valve?

I wish I'd kept one of the failed ones to check.

[cynic]

If the sensor sits in the gas flame its not going to be a simple oven thermostat. Flame failure devices (FFDs) which this appears to be sit in the flame and register the presence of the main flame. When they do not detect the flame they shut the gas supply down to pilot gas rate to stop gas pouring at high rate into the oven and hence the room. Whats the part number and what cooker does it belong to as the photo you linked to doesn't give sufficient detail to know what its full function is, however I would expect an oven stat to have a sensor bulb high up in the baking space and respond to the surrounding temperature according to the gas regulo number or temperature you set on the control knob.

[Reentrant]

this:

>>> Changing it is relatively straightforward - I've done it twice now -

D'oh you're right - I was confusing two separate repairs. The bulb on the Flame Sensing Device looks rather like the thermostat bulb (p/n

930751900) that lives in the top of the oven.

I'm still impressed that such thin copper tube manages to work without kinking and blocking the capilliary.