Lennox Diplomat Furnace

Problems related to residential installations.

Lennox Diplomat Furnace

Postby sam » Tue Nov 06, 2012 2:08 am

I’m having a problem with a Lennox Diplomat furnace. I am getting a 2 LED flash error code which indicates the flame cannot be sustained. The flame shuts down after about 10 seconds and tries to re-ignite. Sometimes it does and sometimes it doesn’t. A couple of times I decreased the setting on the thermostat and waited for about 5 minutes. I increased the setting on the tehermostat and the furnace did exactly as described above. Any suggestions?
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- Lennox Diplomat Furnace

Postby Freon » Wed Nov 07, 2012 4:10 pm

Most likely you have a dirty flame sensor, out-of-alignment flame sensor, faulty grounding of the furnace frame or a bad control circuit.

The flame sensor is a rod that has a voltage applied for the purpose of creating a current flow through the actual flame. A gas flame will conduct electricity. The control board monitors the current flow and if the current is not adequate, because there is no flame, then the furnace is shut down.

The causes for an inadequate current flow can be a dirty sensor rod (clean with steel wool or emery cloth), improper positioning relative to the the flame and the burner (the current has to flow from the rod, thru the flame to the burner or other grounded metal surface of the furnace), or a poorly grounded furnace frame (check all 120 volt wiring back to the main circuit breaker box for good connections).
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