When furnace temps don’t match

Short-cycling fixes

You set the thermostat at a certain temperature, but the furnace never seems to generate enough heat to match your chosen temp. Instead, the furnace stops for a while.

Your problem may be “short-cycling.” It’s wearing down your system and it’s not delivering the temperature you want.

What’s wrong?

• The cause may be in the thermostat. Are the batteries dead or low on power?

• It also could be due to a dirty or clogged air filter that keeps all the heated air from reaching your rooms.

• Also check the flue, which could be clogged by leaves or an animal that crept inside, eager to enjoy your heat.

If none of these is the problem, then you may have more serious concerns.

• The fan limit switch may have died or sensed trouble with the system. This switch is important – it controls the flow of hot air. It will shut down if it determines there is too much heat.

• You may have trouble with the flame sensor, an L-shaped rod that tells the furnace that a flame is present while the gas valve is open.

If the flame sensor doesn't detect a flame, it shuts down the furnace.

And if it gets dirty, the sensor can’t detect flames.

• All these concerns can be fixed, but another issue should be dealt with immediately: If you smell gas building up, evacuate your home immediately and call 911.

Lighthouse HVAC’s experienced technicians repair and install furnaces in Brooklyn, Manhattan, Queens and Long Island. 24/7 service.