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Tony Hwang

wrote:
I have a Rheem Classic 90 Plus furnace. Lately it has been shutting
down, normally at night and sometimes just switching the power off
then back on is enough to get it going. At other times turning the
power off and on will do nothing and then the furnace will start
working again on its own several hours later. We had a technician in
and he checked the furnace over and said because it was intermittent
he couldn't do much, cost $60.00 When the problem next appeared it was
a little different in that the burners would fire up for a couple of
seconds then shut down, then fire up and shut down, then the flame
light would flash on the control board. I cleaned the Remote Sensor
and the spark ignition and sensor and it seemed to work for about 4
days before it shut down again. Now it just tries to cycle on (no
Burn) and then shuts down, keeps trying to cycle on and at some point
is successful as the furnace eventually starts and runs. The other
evening it shut down and it was about 40 degrees when I got up, trying
to recycle the power did nothing. We called a technician right away,
but he showed up 5 hours later and by then the furnace had restarted.
He checked the inlet and outlet pressures which were OK and he said
the air inlet pipe was slanted downward going outside. He corrected
this so now it is slanted up going outside. That cost me $110.00 and
the following morning the furnace had once again shut down. Recycling
the power switch got it going again. The inlet pipe is 4" PVC which
has one 90 degree elbow and then reduces to 2 1/2" PVC going outside,
total length is about 6 feet. The outside inlet pipe is horizontal
with no 45 or 90 degree elbow. There is a moisture hose on the 4" PVC
inlet and there is water in the trap. Could wind or snow blowing into
this pipe cause the above problems? Any other suggestions, it is cold
up here and local technical help is limited where we live?

Hi,
Most furnace retries 3 times before it goes into lock up mode. You can
initialize logic board by powering on/off or it will reset itself to
normal mode after 3 hours or so and try again. With my little bit of
experience, it is usually inducer pressure switch or flame sensor
causing that kind of symptom. Does your logic board give out trouble
code by way of blinking LED? Once I had a problem on logic board. High
Wattage resistor caused a cracked solder joint making the furnace
intermittent. It is a simple sequential logic, to trouble-shoot logical
sequence you need logical mind, LOL! If it reaches a ignition
stage(flame on), next sequence is sensing the flame by sensor and then
after some delay fan comes on. Trying new flame sensor may not be a bad
idea. Also check loose wires/connectors I always keep spare ignitor and
flame sensor.
Good luck,