Rheem heater cycling - http://www.hvacmechanic.com/ Forums
Original message
| tstro
 |  "Rheem heater cycling"
, posted Tue 25 Oct 09:24  
I have a 14 year old Rheem natural gas heater, 80 or 85% efficiency (RGDE-10EQAGR). It is the type that uses the hot surface ignitor also as the flame sensor.
The unit comes on, ignitor lights, gas lights, and runs for about 1.5 minutes to 2 minutes at which point the gas shuts down. The system will then recycle but the next time only run for abut 30 seconds before cycling again.
I replaced the ignitor and adjusted it's postion to make sure it was in the flame. I tested and jumpered the limit controls - same operation. I tested the pressure switch with and ohm meter and it appears to be working - not sure how to jumper it as it has two wires. I checked all connections on the circuit boards and cleaned the unit.
The unit has the older type piggyback circuit card without any indicator codes. There are a few test points on the card but I do not know how to test them.
Any suggestion as to what the problem might be?
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Replies:
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| Freon
| "Re(1):Rheem heater cycling" , posted Tue 25 Oct 15:36
See if you can find the blower/limit switch. In a furnace that old it may be in a 3X5 box on the front of the furnace near the heat exchanger location. The front of the box should come off and inside you'll see a dial with sliders pointing to various temperatures. Call for heat and watch that dial. It should rotate as the main burners are heating. At one point the main blower should come on (middle slider switch). After the blower is on, if the dial keeps going to the last slider (high limit) then you may have a bad switch (that unit slides out) or there's not enough air flow through the furnace causing the high limit to stop everything. Another possibility is the flue limit switch, if present. Be sure your flue doesn't have any nests or other blockage.
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