Here is Why Your Furnace or Boiler Won't Start - Frederick Air, Inc.
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Here is Why Your Furnace or Boiler Won’t Start

While gas furnaces and boilers are efficient, they can have problems like any other mechanical system. When the temperature in your home drops below a comfortable level, you will wonder to yourself: why won’t my heater turn on? There are several common reasons why your boiler or furnace won’t ignite. A few troubleshooting steps that you can take will help you to determine the cause.

Reasons Why Your Furnace or Boiler Won’t Start


Ensure that your thermostat is set to the heat position and that the set point is below the current room temperature. Thermostat settings can be changed accidentally. Lower the setting several degrees below the current room temperature and wait several minutes for the system to activate. If the heating system does not come on, go to the next step.

Electrical Problem

Many of today’s modern boilers and furnaces do not have pilot lights. They use electronic ignition. They may also be equipped with a safety blower that vents combustible gases. Boilers are also equipped with circulation pumps. These components require electricity to operate. Verify that your furnace circuit breakers have not tripped. If they have, reset the breakers. Your unit may also have a service safety switch. It looks like a light switch and will be mounted near your furnace or boiler.  For oil systems, it may be at the top of your steps leading down to the basement. Ensure that it is in the “On” position.

Gas Supply

If the thermostat and power are operating correctly, verify that the system is receiving a sufficient flow of gas. Ensure that the shut-off valve is in the open position. It may have been closed during the summer, when the furnace or boiler was not needed, as a safety precaution.

Faulty Component

The final cause of a boiler or furnace failing to operate could be a faulty component. Parts become dirty and wear out over time. There are air and gas flow sensors that require cleaning, as does the orifice through which the gas flows to the burner unit pilot light. The control valve contains a temperature probe that will shut the system off if the probe malfunctions. The thermocouple is a device that stops the flow of gas if the pilot light is out. The electronic ignition system and condensate pump may also be malfunctioning.

You can check the thermostat, reset circuit breakers and open the gas supply valve yourself, but working on supply lines and replacing system components should be left to a professional to minimize the potential of electrical issues or a future gas leak.

Getting Help

Before the cold weather sets in, have your heating system checked. To schedule a maintenance visit by one of Frederick Air’s highly trained technicians, contact our office. This preventative maintenance checkup can help you avoid potential problems with your furnace or boiler. Frederick Air service technicians are also available 24 hours a day in case of emergencies. Call 301-663-0300 to schedule your appointment or book online by clicking here.

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