No Heat? Self Diagnose Thermostat First


If your thermostat says heat is on, but you have no heat, there are many things you can do to troubleshoot the situation before having to call in a professional, including taking the proper steps to diagnose your thermostat.

Although sometimes there is an actual problem with your HVAC system, you’d be surprised how many times the issue lies with the thermostat itself. Before calling a professional, take the time to do a little thermostat self-diagnosis. No experience is needed.

5 Ways to Troubleshoot Your Thermostat

  1. Check Power, Heat, and Fan. Before moving on to the list, make sure your thermostat is correctly set to “heat,” that the temperature setting is above the room temperature, and that your furnace’s power switch and circuit breaker are on and receiving power. If you are experiencing constant blower or fan operation, check the fan setting and make sure it is set to “auto.”
  2. Check the Batteries. The first thing you want to do is make sure that your thermostat has the power needed to operate. Although some thermostats do not require batteries, most do. If you have never opened up your thermostat housing to replace the batteries, here is a good video showing you how.
  3. Dust the Inside. Since you now know how to open up your thermostat, now is a good time to blow or brush off any dust or debris that has accumulated inside. Especially for older electromechanical models, dust and other material can affect temperature readings and other interior parts. Use a paintbrush or other small brush to remove any dust and a soft piece of paper to get in between the coils and contact plates.
  4. Location, Location, Location. You want to make sure that your thermostat is out of the way of any heat source, including direct sunlight, heating vents, lamps, space heaters, or anything else that may affect your thermostat’s temperature readings. The furnace will not turn on if it already thinks that it has reached the desired temperature.
  5. Adjust the Anticipator and Level the Mercury Switch. The last thing to watch out for is your anticipator’s setting and the balance of your mercury switch. The anticipator is located inside of your thermostat housing.

The anticipator, as the name suggests, anticipates when your cooling or heating cycles should turn on or off. If you find that your furnace (or A/C) turns on and off too frequently (or not frequently enough), you should adjust the anticipator’s setting. If the heat never seems to reach the desired temperature, turn the anticipator’s small metal adjustor away from the “longer” setting and closer to the shorter setting (and vice versa).

The mercury tube in your thermostat also needs to be adjusted if necessary. Make sure that your thermostat and mercury tube are exactly level. Use a laser level or other tool to straighten your thermostat.

Other Solutions

If none of these steps have solved your problem, you either have a mismatched thermostat or the problem lies within the furnace itself. The best way to make sure you have a reliable and efficient heating system is to have thermostat installations done by a professional who can correctly match the thermostat to your system and always remember to schedule annual heating and cooling tune-ups.

Before calling us, however, make sure you have a clean air filter in your furnace and that the blower door is completely shut. Sometimes it’s a little fix and does not require professional service.

Heating and Cooling Des Moines Since 1997

At Service Legends, we take pride in heating and cooling Des Moines and the surrounding areas. Our HVAC services include furnace and air conditioner installation, repairs, maintenance, and tune-ups. Our lineup of Indoor Air Quality solutions includes whole-home humidifiers, air purifiers, and air filtration systems. We can even help with HVAC financing.

Call 515-657-6634 to contact our Home Comfort Heroes today. We’re standing by 24/7.

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