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Posted by Tony Hwang on February 16, 2007, 8:24 pm
bcooper@adga.ca wrote:
> Tony Hwang wrote:
>
>>bcooper@adga.ca 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,
>
> If it was a consistent problem it would be easier to fix. The first
> time it went off for a long time, well over 3 hours and would not come
> back on by recycling the power. The next time it would reach ignition
> stage for a few seconds and then shut off then reach ignition again,
> then shut off and show a blinking Flame LED. This was when I cleaned
> the Flame sensor and the Ignitor and Sensor combination. This worked
> for a few days. Now, at least this morning, it would not get to the
> ignition phase until I reset the power. The furnace has worked well
> since this morning, but I am worried about tomorow morning. I
> understand the logical sequence, but this is not logical, it is random
> and that much harder to diagnose. This furnace is about 6 years old
> and all the wires/connectors seem fine and there is no noticeable
> cracking anywhere on the logic board. The technican supposedly checked
> the pressure switch and said it was working to specs. Any other
> suggestions?
>
Hi,
If logic board has cracked or cold soder joints by vibration of heat
from big resistor, it's underside of the board.(opposite of component
side)
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