I have a gas fireplace which the pilot won't stay lit. It lights but shuts down when I turn the valve to "on."
The gas valve is a Robertshaw.
The thermocouple puts out 0.5 volts. What I don't understand, the pilot light circuit includes a Robertshaw mercury switch in series with the thermocouple. I've attached a schematic. It appears this mercury switch is bad. If I short across the mercury switch terminals the pilot light stays on and the fireplace lights and works fine. Why is this switch there? Seems like it isn't necessary. Is it really needed? The switch probe is next to the thermocouple probe at the pilot light. Mercury switches are hard to get. From what I can find, Robertshaw does not make them anymore. The other switch in the schematic is just an on/off switch to light the burner.
Thanks for the help!