What does it do?
send a low voltage signal to the gas
valve, letting the gas valve know there
is a flame and it can stay on.
Why do they go
out? Nothing lasts forever. after a
while a thermocouple is no longer able
to send enough voltage to the gas valve
to keep the pilot button set. and it
needs to be replaced. Some times you can
just relight the pilot and it will hold
for a few days then go out again. Most
of the time this is a week thermocouple.
How to replace
thermocouple scroll down for
First thing that I need to
make clear is the difference between a "Gas Valve" and a "Gas Cock" Many people
call the gas cock a gas valve, but for the purposes of this page I will refer to
it as the gas cock to avoid confusion. all images on this page are thumb nails
click on the image to see a larger version of it.
The Gas valve is the main control of
the gas going to your appliance. There
are many different kinds of gas valves.
The one in this picture is from a Weil
McLain boiler, it is a 24 volt standing
pilot gas valve. Not all gas valves are
24 volt standing pilot. and not all Weil
McLain boilers have this type of gas
valve. Some are mili volt and use a
thermopile instead of a thermocouple and
are not interchangeable. Others are 120
volts. and are also not interchangeable.