On 26 Feb 2007 08:20:18 -0800, wrote:

I'm trying to get an idea of what my problem might be. The thermostat
triggers the furnace, one by one the gas flame jets start going, then
they cut out, then one by one they try to start up again, then they
all die out except for an orange glow, then the blower comes on and
shoots out the cold air. I turned off power to my furnace for half an
hour, and when i turned it back on, and it worked as expected.
Anybody have any thoughts to the problem?


Take a look at your fan belt and see if it actually drives the fan
when the motor comes on. When the burners fire up and and fan does
not run, the heat exchanger gets over heated fast. The temperature
overheat sensor then cuts off the burners. But the part where you
said that by switching off the furnace and then turning it on restored
normal function will need a recurrence of the problem to nail down the
problem.

Watch for this. The delay in the fan starting up may be due to the
fan belt being old and glazed, due to incorrect tension or even worn
bearings. When the opportunity arises you might as well undo the fan
belt and take out the squirrel cage assembly to do preventive
maintenance. Use the opportunity to vacuum and wipe clean the furnace
compartment and to clean the squirrel cage. Note the direction of the
vanes and reinstall the same way. Take out the bearings and check
against the shaft for wear. The bearings' holes may be ovalled.

Should you need to replace the shaft or the bearings do not use any
grease or lube oil. They are dry bronze bearings and any grease or
lube will be cooked dry by the heat and cause problems. Replace with
a new belt anyway as the cost is negilble. Tension the belt so that
the weight of the motor can just rotate the squirrel cage without
slipping.