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?
On Feb 26, 11:20 am, email@example.com wrote:
well it could be a number of things. If you are very low on gas (on LP
gas) or your pressure regulator (at the supply head) is frozen it can
easily cause this problem and is most likely. You could also have a
bad thermal cutoff switch telling your furnace's gas valve to cut
best bet is the first option. It really sounds like you're low on gas
pressure. If you find that your gas supply is just fine and there are
no problems there- your best bet is to call a licensed professional to
have them service your furnace.
On 26 Feb 2007 08:20:18 -0800, firstname.lastname@example.org wrote:
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
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
hmmm, fan belt, I'm not sure his unit is that old. I haven't seen a
fan belt on a residential furnace ever.
I agree with the low pressure of the gas, the regulator maybe.
Another thing that was eluded to is this, the thing that starts your
fan in heat mode is a temperature sensor in the furnace. When the gas
first ignites, it heats up the heat exchanger and a temp sensor senses
that the furnace has warmed up and then turns on the fan. Also, when
the gas shuts off, the fan continues to run until the temperature
sensor in the furnace gets down to the shutoff point.
How long do your burners shoot out flames before they shut off? If
it's more then about 15 seconds, then the furnace temp sensor that
tells the fan to come on may have not been working and the burners
stayed on until the high limit temp sensor cut them out, the furnace
cooled some and the burners came back on but then the high limit cut
them out again. I'm guessing maybe the temp sensor that turns the fan
on was flakey or if your unit is new enough, the electronic board
malfunctioned and the reset cleared it.
The high limit temp sensor is a safety and keep the burners from
running too long without the fan blowing, ie, the furnace would get so
hot it would burn up the house.
What is the furnace brand? Take the door off and see if there is a LED on
the board that flashes while it goes through its sequence of operations, if
so find a trouble shooting guide and follow the instructions.
Have you had anybody work on it in the past? If so, did they change out the
control board or fan motor? Some furnaces when you change the intergrated
control board need a separate wire that comes in another kit, if you change
the board in A/C you wont notice until Heat that you did it wrong. It could
also be caused by someone changing the fan motor and not reconnecting the
ground wire properly.
Could be the negative pressure switch getting weak and not keeping
If you have L/P make sure it was converted, if not converted, the manifold
may have gotten clogged with ash and the over temperature switch may be
tripped. If you have natural gas don't worry about any frezzing valves or
whatever that guy was talking about.
My guess would be the negative pressure switch, they are easy to check if
you have the right tool.
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