How to Change a Thermostat

By Dave Rongey - Summary:

Thermostat Problems and How to Fix Them: Wiring a Heating and Air Conditioning Thermostat.

Replacing a Thermostat

Electrical Question: I have two thermostats, one downstairs in the hallway and the other one is upstairs in my bedroom. I wanted to replace them with a digital thermostat. I was able to change the downstairs thermostat, but when I tried to do the upstairs I had no success.

  • Installing a Digital Thermostat
    I bought two digital thermostat at Lowe’s, not knowing that the thermostat upstairs required a thermostat that has some kind of pump. Well I did the one downstairs first, got it hooked up & it worked, went up stairs took the White-Rodgers old thermostat off & put in the Honeywell, I got done wires crossed, so I called Honeywell, that’s when she told me I had the wrong thermostat for upstairs. I needed a special one that’s for a pump.
  • Exchanging the Thermostat
    I take that one back, get the one she told me to get, hooked it up, didn’t work, I got so frustrated, I just took it back & got a refund. I tried to put the White-Rodgers back on, and it didn’t work either. Hmm.
  • The Power Supply
    It was working fine before I took it off the first time. I really feel like I blew something inside the house. No smoke or burnt smell taken place. How do I go about finding if I blew a fuse or a circuit breaker?
  • Problem with Two Thermostats
    the I would like to check that first before I call a air & heating person. I really would like to go digital. One is fixed and the other is broken. I have not run the downstairs because I don’t want to put stress or wear and tear on it by trying to cool the the whole house.

What do you think I did wrong?


This electrical question came from: Jason, from Atlanta, Georgia.

Dave’s Reply:
Thanks for your electrical wiring question Jason.

Wiring a Heating and Air Conditioning Thermostat

Application: Replacing and Installing a Thermostat.
Skill Level: Beginner to Intermediate.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on personal level experience and ability to work with tools.
Precaution: Identify the circuit for the furnace or heat pump, turn it OFF and  Tag it with a Note before working with the thermostat wiring.
Troubleshooting and Testing: Most thermostats may be tested using a Volt/Ohm Meter. The thermostat battery should be tested and replaced as needed.
Notice: Make sure to get the exact replacement thermostat.

Guidelines for Replacing a Wall Thermostat

Replacing a Thermostat can be tricky, but it is possible when you follow these Guidelines

  • All thermostats are not alike, some work with Low Voltage, and some with Line Voltage or the circuit voltage.
  • If the wiring is not small similar to door bell wire or telephone wire the the thermostat may be Line Voltage.
  • When replacing any thermostat the circuit for the equipment must be identified and turned OFF.
  • Make a drawing of the wiring connections BEFORE removing any wires, or take a photo or two with a digital camera.
  • Make sure to get the right replacement or one that is compatible.
  • Purchase a good quality brand thermostat which has a toll free support phone number or website which will assist you if you have problems. Take your time be patient and don’t break any wires.

Common Thermostat Problems and How to Fix Them

  • The Thermostat Battery is Dead and Needs Replacing

    • Not all thermostats have a battery, but most digital or programmable thermostats do have a AA Battery in the wall mounted thermostat.
  • Problems with a Energy Saving Programmable Thermostat

    • When a home has been equipped with energy saving devices often a programmable thermostat is installed and the programming may be very difficult to understand and the digital display may be difficult to read or understand.
  • Default Program Settings

    • Most energy savings thermostats work very well and have a default program and only a few settings are required which are best programmed by the installing service technician.
    • If a programmable thermostat is too difficult to understand or is not performing then a non-programmable standard thermostat may be a better solution, such as a Honeywell or White Rogers thermostat.
  • Make sure the heater or air conditioner has power to the unit

    • The circuit power to the heater, heat pump or air conditioner must be available and working properly otherwise the heating and air conditioning system will not work even if a new thermostat is installed. A HVAC, Heating Ventilation and Air Conditioning technician should be called to check the HVAC system and the circuit power and components.

More about Wiring a Thermostat

How to Install a Programmable Thermostat for Room Heating Unit

Electrical Circuit for Caret Baseboard Heaters: When we tried to convert from ceiling heat to a cadet baseboard heater we found three bedrooms were all on the same circuit.

Wiring Instructions for a Honeywell Thermostat: I bought a Honeywell Heating thermostat. There were no directions about how to wire it.

How to Install Electrical Wiring for a 240 Volt Wall Heater

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2 Responses to “How to Change a Thermostat”
  1. Dave Rongey says:

    Hi Jer,
    The thermostat that you are describing is typically used to control the 240 volt circuit, consisting of the Line and Load circuit wiring. Please refer to the wiring diagram which is included with the thermostat of the baseboard heater.
    I hope this helps,

  2. Jer says:

    I bought a cadet 6 foot baseboard heater and they sent me a 4 pole thermostat and I only need a 2 pole, how can I make the 4 pole one work? or can I?
    Thanks, Jer


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