Isolating a Furnace, Bypassing the Thermostat

Every day we receive many calls from frustrated technicians who are dealing with error codes on furnaces that, seemingly, can only be explained by a faulty control board. These codes may vary, but the consistent description is that the board is giving a code that “cannot exist”. One such example would be a pressure switch code when the pressure switch is clearly closed to the board.

One of the first tests that we will have technicians run is simply disconnecting all of the thermostat wires from the control board and jumping “R” to “W”. This may seem overly simple or elementary, but it is amazing the number of furnaces that are made to run correctly simply by removing the thermostat and thermostat wires from the system.

Keep in mind, the thermostat may be “functioning” properly; it may be calling for heating, cooling, or fan as commanded. But there are cases where the thermostat is found to be directly interfering with the boards’ performance. In these cases, the thermostats will need to be replaced.

We recommend that, if jumping “R” and “W” seems to allow the furnace to run correctly, you cycle the furnace multiple times before replacing the thermostat. This will ensure that the furnace itself is actually consistently working correctly.

Jeff Rosenblum
Technical Support
16 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

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