5 Reasons Why Your Furnace Won’t Ignite

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The thermostat says your furnace should be heating your home, but the system just won’t light. What now?

Fortunately, there are a few troubleshooting steps you can take to get your furnace going before you call a technician. Below are some of the most common problems that prevent furnaces from igniting, along with some tips to solve them.

1. Your furnace isn’t getting power.

Even if you own a gas-powered furnace, if it has an intermittent pilot light or hot surface ignition, it still needs electricity to ignite. Therefore, if the power is shut off to your furnace, it won’t light. Check the circuit breaker panel and see if your furnace tripped the breaker on its circuit.

If the circuit breaker is still switched on, look for an ON-OFF switch next to your furnace. Make sure that this power switch is turned on so that the unit can receive electricity.

2. The furnace door isn’t properly shut.

Most furnaces are equipped with at least a few safety features. In some models, that includes the door of the furnace itself. If it isn’t closed snugly, then the unit won’t light. Try opening your furnace’s door and closing it until snaps firmly into place.

3. Your furnace isn’t getting gas.

First, check to see if other gas-using appliances are getting gas. If you have a gas stove or range, see if it will light. If it does, then you know that gas isn’t going to your furnace specifically.

If the rest of your home is getting gas but your furnace won’t light, check your furnace’s gas shut-off valve. Sometimes the valve will get turned off by a technician for safety reasons while they service the unit. It’s also possible that someone in your home switched the valve off at the end of the last heating season as a safety precaution.

If the shut-off valve lever is perpendicular to the gas line (forming a “T” shape), then the valve is closed, and gas is not reaching your furnace. To turn the valve on, adjust the level until it’s parallel to the gas line.

4. Your furnace doesn’t have the correct “gas-to-air” ratio.

In a natural gas furnace, the flame is actually fueled by a mixture of natural gas and oxygen. The gas-to-oxygen ratio can become altered over time. When that ratio changes, it can result in delayed ignition: in other words, your furnace takes longer to light than it should.

When a safety device in your furnace detects that gas is filling up the combustion chamber without igniting, it will kill the gas supply to your furnace to prevent the gas from exploding when it finally does light. In newer furnaces, that safety device is the flame sensor, and in older furnaces, it’s the thermocouple.

For any gas-related repair or maintenance on your furnace, it’s essential that you involve a licensed and trained professional to avoid safety hazards.

5. There’s an issue with your furnace’s ignition sensor or thermocouple.

As mentioned above, the flame sensor in new furnaces and the thermocouple in old furnaces will shut off the gas supply if they detect that the furnace is taking too long to light. However, there’s always the possibility that the safety device itself is faulty or that there’s something affecting its performance.

For instance, a flame sensor can:

  • Accumulate dust
  • Corrode from carbon buildup
  • Move out of position

These issues can best be prevented by routine preventative maintenance.

Heating Services in Winston-Salem

At Logan Home Energy Services, we’re proud to offer quality heating system repairs, replacements, and maintenance with unmatched customer service. Schedule your appointment by contacting us online or giving us a call at (336) 203-7630.

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