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Top 12 Problems/Mistakes when Installing or Replacing a Thermostat! HVAC Tips!


We have had many questions and problems about thermostats and about thermostat installation problems. I found a very good video on the ACservicetech youtube channel. Please click here if you are interested in seeing some of the many outstanding HVAC service and troubleshooting videos.   Below we have an excellent Youtube video that I copied from the ACservicetech channel which shows 12 problems, mistakes that we can make when installing or replacing a thermostat. I hope this helps you out. If you have any questions please email me, Steve Arnold, anytime. Our email address is We would love to help you out and earn your business!

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2 thoughts on “Top 12 Problems/Mistakes when Installing or Replacing a Thermostat! HVAC Tips!

  1. Ok… We have a johnston Fraser model # emjm514879. Earlier in the year the furnace was stunning fully operational when lighting struck… ?? the house? near by? Right after the strike I noticed the blower motor was running and the igniter was cherry red. The inducer motor was not working. (Quickly unplugged the furnace.) Fast forward… Replaced the control board and inducer motor. Now we plug in the furnace, turn up the thermostat and blower motor kicks in and runs constantly. Igniter does not light up and inducer motor does not kick in. Control board is flashing/blinking slow green. What is the problem?!

    1. Hi Amanda! This most certainly sounds like the lightning strike messed up your furnace and may have messed up many of the controls on your furnace. I am sorry, I do not have a Johnston Fraser parts program where I can look up parts to see what parts you have on your furnace. This sure sounds like it is electrical related because the first thing that should happen when calling for heat is that the thermostat should send a signal to the control board through the W (white) wire and the control board should start the draft inducer. I would suggest checking your thermostat wire connections to make sure when the thermostat is calling for heat that you are getting 24 to 28 volts AC between the R and C (com) terminals, W and C terminals. You should not be getting 24 volts between the G and C (com) terminals. Power through the G and C terminals would cause the fan to run all the time. I would suggest disconnecting the green wire and see if this solves the problem with the blower running all the time. If you are getting 24 volts between G and C then you have a thermostat problem. I would suggest that you check all rollouts (if equipped) and limit to make sure the limit and rollouts are all closed and not open. We have lots of furnace troubleshooting advice on the following page: I would suggest going through the troubleshooting flow chart to see what is wrong: We also have lots of troubleshooting questions and answers on the following page: If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem.

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