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I recently replaced my flame sensor and Robertshaw SP735L control module with a new ICM293 control module on my Lennox G20 furnace. This seems to fix the erratic pilot sense issue I was having, but it created another problem - my blower won't stop blowing air.

The thermostat is in the heat setting and the fan in the automatic mode. If I call for heat, the furnace operates as expected. It's when you've reached your heat setting and the unit turns off the gas heat (flames go off and damper door closes), the unit continues to run the blower continuously instead of turning off after 90 seconds per the jumper setting on the BCC. It even runs the blower motor if I turn the thermstat setting to 'off'. I made sure the green (fan) thermostat wire was not getting 24VAC and even went the extra step to remove the green (fan) thermostat wire from the BCC circuit board terminal so I know the turn on blower signal is not coming from there.

I reinstalled my original Robertshaw SP735L control module and the blower turns off as expected (90 seconds after gas heat has switched off). I suspect this tells me that the BCC timed blower off circuitry is operating correctly. Reinstalling the ICM293 once again results in the same blower not-turning-off issue.

Has anyone experience this odd issue. Supposedly, the ICM293 is a suitable replacement for the Robertshaw SP735L.

Thank you in advance for any insights!


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Personally I have found ICM replacement aftermarket control boards to be of much lesser quality than OEM and have had problems with them not only failing shortly after installed but bad out of the box. I make this comment knowing what few OEM boards have this kind of problem from my experiences.
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