"bill horne" wrote in message
...
I have a 20-year old Carrier 58SS furnace with a 646A-X gas valve converted
for LP. Beginning at the point in the heating cycle when main burners are
burning, the symptoms a

- When the thermostat is satisfied, the main burners turn almost off, but
continue to burn for about 5 seconds with much reduced vigor, and with 2-4
inch orange flames burning vertically from the orifices.

- the pilot continues to burn, but also with a much smaller flame.

- later, when the thermostat calls for heat, the main burners never light
off.

Troubleshooting revealed the following:

- if the gas supply is turned off, the pilot, of course, goes out, and if
the gas supply is turned back on, the pilot hisses.

Workaround is:

- when the thermostat is satisfied, and the main burners go nearly out, I
turn off the gas supply and the thermostat.

- when I want heat, I turn on the thermostat, the igniter starts sparking,
and I turn on the gas supply. The pilot ignites, and in less than a
minute, the main burners ignite normally.

I speculate that the gas valve is not closing completely when the
thermostat is satisfied, and if I'm correct, can the valve be fixed
(cleaned?), or must it be replaced?

You REALLY need to call in someone that knows what they are doing. A gas
furnace is nothing the experiment with......