My Miller gas furnace occasionally stops in mid cycle, the ignitor works, gas starts up blue, just as it starts blowing it goes ''poof'' and shuts off, but the fan keeps blowing for a few minutes. It is getting worse. lately it has also started up again immediately after a successful cycle ends (Like the fan will shut off as usual, and then click, it starts up again....Help?
If the flame looks good prior to the room air blower starting but becomes unstable when the blower starts, you have a crack or hole in the heat exchanger. I strongly suggest your technician do a test on it to see.
1. Thermostat calls for heat.
2. Draft inducer motor starts.
3. Pressure switch attached by a small plastic or rubber tube senses the negative pressure produced by the draft inducer and closes.
4. Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small metal probe about 1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops with no ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back off and on again. Then the sequence starts all over again with no ignition of the gas.
Solution:You probably need to purchase and install a new ignitor. I would suggest that you inspect your ignitor closely for cracks.Make sure you do not touch the ignitor with your bare hands. If you do not visually see a crack, then you could have a furnace control board problem or a limit, rollout switch problem. Please see "limits, rollout switches & furnace control boards" further down on this page. The furnace's control board might not be supplying the voltage to the ignitor. If your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then you need to clean your flame sensor with light sand paper or steel wool. You might need a new flame sensor, but most of the time they can be cleaned an will work well after cleaning.
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1.
Thermostat calls for heat.
2.
Draft inducer motor starts.
3.
Pressure switch attached by a small plastic or rubber tube senses the
negative pressure produced by the draft inducer and
closes.
4.
Draft inducer runs for 30 seconds to a minute before you hear a gas hissing sound. The ignitor did not glow, the flame sensor (a small
metal probe about 1/8" in diameter, with a white
porcelain base) does not sense the flame, so after 8
to 10 seconds the hissing sounds stops with no
ignition of gas to heat your home. Your furnace shuts down and goes into a lock out condition until you turn your power switch back
off and on again. Then the sequence starts all over
again with no ignition of the gas.
Solution:You probably need to
purchase and install a new ignitor. I would suggest that you inspect your
ignitor closely for cracks. Make sure you do not
touch the ignitor with your bare hands. If you do not
visually see a crack, then you could have a furnace control board problem or a
limit, rollout switch problem. The furnace's control board
might not be supplying the voltage to the ignitor.If your furnace
lights and the gas stays on for 8 to 10 seconds, then shuts right back off, then
you need to clean your flame sensor with light sand paper or steel wool. You
might need a new flame sensor, but most of the time they can be cleaned an will
work well after cleaning.
1. Thermostat calls for heat.
2. Draft inducer motor starts.
3. Pressure switch attached by a small plastic or
rubber tube senses the negative pressure produced by
the draft inducer and closes.
4. Draft inducer runs for 30 seconds to a minute
before you hear a gas hissing sound. The ignitor did
not glow, the flame sensor (a small metal probe about
1/8" in diameter, with a white porcelain base) does not sense the flame, so after 8 to 10 seconds the hissing sounds stops
with no ignition of gas to heat your home. Your
furnace shuts down and goes into a lock out condition
until you turn your power switch back off and on
again. Then the sequence starts all over again with no ignition of the
gas.
Solution: You
probably need to purchase and install a new ignitor. I would suggest that you
inspect your ignitor closely for cracks. Make sure
you do not touch the ignitor with your bare hands. If
you do not visually see a crack, then you could have a furnace control board
problem or a limit, rollout switch problem. The furnace's
control board might not be supplying the voltage to the ignitor. If
your furnace lights and the gas stays on for 8 to 10 seconds, then shuts right
back off, then you need to clean your flame sensor with light sand paper or
steel wool. You might need a new flame sensor, but most of the time they can be
cleaned an will work well after cleaning.
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Thank you , but No, the flame stays consistant, I checked, The problem is intermittent, but happens at least once a day. If I "reset" the thrermostat by turning it off, moving the temp dial up and down and then setting on 70 again, then it usually works fine for the next several cycles. However I usually awake (The coldest hours of the morning) to hear it miscyclingg again..
UPDATE" The fast cycling has been solved with new filters (I know... I know :-(), but the intermittent shutting off right when the blower starts is still happening.
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