The diagnostic light blinks 6 times since I replaced the circuit board that a HVAC tech said was bad. Apparently that was not the problem it still stays on. I have replaced the therostat with a new one. The T/S chart says it's a 115 VAC polarity problem or a grounding problem. How do I know? Nothing has changed with the plug for a ground. Does the thermostat have anything to do with the polarity of something? Mike

The make and model of the furnace will be a big help. If a leg of power was reversed in the process of changing the control board or working on that code will show up. Is this a system that has two units twinned together?

It is a Trane XR80. No this is a single unit. The fan ran before changing out the control board. It still runs after the board change so I am confident the board didn't have an effect on the fan problem. I think I have 2 different problems but I am not an HVAC tech. Thanks for helping so far. Mike

Quote:

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Originally Posted by air0mjb

It is a Trane XR80. No this is a single unit. The fan ran before changing out the control board. It still runs after the board change so I am confident the board didn't have an effect on the fan problem. I think I have 2 different problems but I am not an HVAC tech. Thanks for helping so far. Mike

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Did you try to reverse polarity of the power going to the furnace to see if it gave the same code?

Trane XR80 furnace provides a LED on its integrated furnace control for quick diagnostic. Here is its diagnostic code:

LED Flash Error
Flashing Slow Normal No Call for Heat
Flashing Fast Normal Call for Heat
Continuous On Replace Control
Continuous Off Check Power
2 Flashes External Lockout (Retries or Recycles Exceeded)
3 Flashes Pressure Switch Error
4 Flashes Open High Limit Device
5 Flashes Flame Sensed when NO flame should be present
6 Flashes 115 VAC power reversed polarity or poor grounding
7 Flashes Gas Valve circuit Error
8 Flashes Low Frame sense Signal
9 Flashes Check Ignitor

I have the diagnostic chart. The unit is 4 years old and was running fine until the fan kept running. If the circuit board is fine and now the light blinks 6 times why would changing the leads on the plug fix the problem? I didn't touch anything with that. What ground are they talking about? Would it be in the power cord. I have a 1951 house and there is no grounds through the outlets. It's a 2 wire system, but it was hooked up like that for 4 years with no problems so how could it be a grounding problem?