Tricks of the trade

How to diagnose common central heating system problems

Heather Mahr, a Ferguson author

by Heather Mahr


Cold weather makes furnaces and heating systems work overtime to warm a space, which means heating and cooling professionals often have to work overtime as well. Central heating systems are complex and have a wide range of components that can malfunction, especially at night when temperatures drop. When a customer calls you in the middle of the night because they lost heat, it’s important to have the right parts on hand to help you troubleshoot and fix heating issues. Make sure your heating and cooling business is ready to tackle an influx of service calls around the clock this winter with our list of common heating problems. Keep your customers warm by stocking your work truck with the proper HVAC equipment to help you diagnose and repair heating issues fast.

Tips to diagnose and tackle common heating problems

  1. Nothing happens when I turn my thermostat on.

    HVAC professionals know that there are a number of reasons why a thermostat could fail to activate a heating unit. HVAC professionals also know it’s better to start with the simplest solution first, then work towards troubleshooting the more complicated problems. After checking the circuit breaker to make sure the thermostat is powered, the next step is to inspect the thermostat itself. If the thermostat components are in good repair, a more advanced reason for a heater to fail to activate when the thermostat is switched on could be the control board. If the control board goes bad, it can lead to complete heating system failure.

    Pro tip: Make sure to keep your voltage meter at the ready in your tool belt to help you check electrical connectivity to the thermostat and other heating unit components.

    Bonus pro tip: Because heating systems often vary from one customer to the next, it’s smart to stock up on a wide range of heating repair parts that work interchangeably from unit to unit.

  2. The heater is running, but warm air isn’t blowing out.

    If the customer switches on their thermostat and hears the heater run but their house is still cold, then it’s time to open up the heating unit and take a look inside. A defective furnace ignitor could be what’s preventing a unit from producing heat, or a fan limit control switch that isn’t sensing heat that is being created. If the limit control switch works, then it’s possibly a defective blower that is failing to push out heated air.

    Pro tip: Consider offering a biannual HVAC system inspection service at low or no cost to your customers. This will help you spot possible heating system problems before they happen and ensure repeat work for your HVAC business.

    Bonus pro tip: In gas furnaces, don’t assume there’s something wrong with the furnace itself. It’s not uncommon that the lack of heat could be due to the gas being turned off from the regional gas company for gas-powered heaters.

  3. My heater runs and my house is warm, but my power bill is high.

    It’s not surprising for HVAC professionals on service calls to find that a customer forgot to change their air filter. Failing to change air filters allows dirt and dust build up inside the heater, and can eventually block air ducts and diffusers. This causes the heater to run less efficiently, and makes power bills soar. Another reason for high heating costs is improperly sealed air ducts that allow heat to escape. Sealing your customers’ ducts can help you cut their energy costs by up to 30%. Saving a customer that much money will likely make them your customer for life.

    Pro tip: If a customer’s central heating system is operating correctly but their power bill is still high, offer to upgrade their old thermostat to a new programmable thermostat. Recommend a thermostat with wifi connectivity so your customer can adjust their temperature setting from an app on their smartphone wherever they go. This will help them save energy on heating when it’s not needed, and they’ll have you to thank. will help you be ready when service calls spike this winter. Stock up on the heating and cooling parts you need to keep your customers warm in cold weather.

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Heather Mahr, a Ferguson author

Heather Mahr

As a writer, Heather is dedicated to providing readers with valuable information. She is passionate about helping people find the answers they need to make their life easier with her words.