How to Troubleshoot a Thermostat

Is your furnace or air conditioner not working and you suspect the thermostat? Here's a way check it.

Things You'll Need

• Screwdriver

Instructions

1. 

   Check Thermostat Temperatures

   There are two temperatures to take into consideration when dealing with a thermostat, set point temp and room temp. Set point is your desired temp and room is your space temperature. So heating equipment will be running when your set point is above room temp. Cooling equipment will be running when your set point is below room temp. If the room temp seems off, check it against another thermometer. A digital thermostat can usually be calibrated. Mercury thermostats cannot be calibrated, but need to be level in order to work correctly.

2. 

   Calibrate Room Temp

   If the room temp seems off, check it against another thermometer. A digital thermostat can usually be calibrated. A user's manual will be necessary to do this, every thermostat is different. Mercury thermostats cannot be calibrated, but need to be level in order to work correctly.

3. 

   Check Connections

   Remove the cover off the thermostat. You will expose the thermostat wire connections. R, W, Y, G, C are the most common connections. R is 24 volt power, W is heat, Y is cooling, G is fan, and C is the common side of the 24 volts. If there is no wire to C the thermostat is battery powered. Depending on how the thermostat is set, R will internally connect to W, Y, or G telling the corresponding equipment to come on. Make sure all connections have good contact and are tight.

4. 

   Take the Thermostat out of the Equation

   To take the thermostat out of the equation YOU need to do what the thermostat does internally. Shut off power to furnace. Once the power is off label and remove the wires from the thermostat. Remember all the thermostat does is connect R to W, Y, or G. So twist the R and W wire ends together, turn power back on and the furnace should come on. Check R to Y and R to G and make sure the cooling and fan come too. If all your equipment is coming on, then your thermostat was the problem.

Tips & Warnings

• Make sure power is off when touching wires.

Resources

• Save on Heating and Cooling