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I bought Ecobee Lite thermostat last summer and connected it properly to the furnace using C wire. Air conditioner worked without any issues. But no luck with the heat. When the furnace gets the call from thermostat the exhaust fan starts but no glowing on HSI. Asked my neighbor (HVAC certified) to take a look into this problem. He measured all voltages and resistance but did not give me any answers. Installed the jumper between R and W wires and furnace gets heat right away. After he installed the brand new thermostat with C wire - no luck. I called another tech and he said my thermostat (Ecobee) is broken. He installed the thermostat( simple one with batteries inside) without C wire (Rh and Rc have jumper) and furnace has heat. So I realized, before I switched to Ecobee my old LUX thermostat was operated without C wire. The furnace is 19 years old and the brand is HEIL.

Can someone give me some directions how to trace the problem? Would be possible even to resolve the issue and use smart thermostat?

I tried to eliminate C wire and even installed ecobee with the PEK - no luck.

Thank you.

  • There's something wrong with your description because you would never put a jumper between R and C (Rc is not the C wire). That would be shorting out the transformer which would either blow a low voltage fuse or eventually cause the transformer to fail. A call for heat is typically R connected to G for the fan and R connected to W for heat. – JPhi1618 Nov 13 '19 at 15:30
  • You can edit your question to clear up any confusion. Unless you call for the fan and heat, there could be a pressure sensor that doesn't allow the ignition to begin. – JPhi1618 Nov 13 '19 at 16:26
  • I edited my question as you suggested. Why is pressure sensor works when thermostat is not connected to C wire? – Serghei T Nov 13 '19 at 16:57
  • It could be that the "C" wire isn't properly wired. Since the system works with a "dumb" thermostat, the C wire could be wrong, or there could be a software setting on the ecobee to select the correct type of heating system. For instance, if it was accidentally set up for a heat pump application, it might not work properly with a standard furnace. – JPhi1618 Nov 13 '19 at 17:01
  • "C" wire goes directly to C terminal on the board. Even I sent pictures to Ecobee tech support person and we verified that thermostat wired properly. The second brand new thermostat (not the smart one) that requires C wire does not work either. I will get home and measure the voltage between C and R terminals on the board, resistance between the C terminal and other ground point and visually inspect the preasure switch. Thank you for your help. – Serghei T Nov 13 '19 at 17:14

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