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 are:
- 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?
Thanks.