Why Does My Furnace Sometimes Turn Off at Night?

Woman trying to adjust thermostat after furnace stopped working overnight

Person shivering under a blanket because their furnace shut off.

As the winter season approaches, it is important to remember our furnaces work the hardest during the coldest parts of the day. This is usually in the wee hours of the morning and overnight. Unfortunately, this is also when the furnace may shut down.

Why Does Your Furnace Stop Working at Night?

If your furnace stops working at night, it may be that your furnace cannot drain the condensation as fast as it is produced. Blockage typically absorbs the condensation and may even drain without any problems, but because it is especially colder at night, your furnace may turn off if the condensation cannot drain.

Other reasons why your furnace keeps shutting off include:

  • Your furnace is too large for your home and is short cycling
  • Your furnace's heat exchanger is overheating due to low airflow
  • Your furnace's flame sensor is dirty

How Do Furnaces Work?

A 90% efficient condensing furnace operates through two three-inch PVC pipes. One pipe pulls in air for the combustion of the main burners. The second is an exhaust pipe to expel flue gases. These types of furnaces only lose 90 to 100 degrees of heat through the exhaust when compared to older furnaces losing four to five times more heat through the flue. With this in mind, the 90% furnace can’t heat the flue piping as older furnaces do, thereby creating condensation.

The condensation, with design, simply drains back to the furnace and is routed through a series of rubber hoses to an integrated condensation trap. These furnaces have a motor strong enough to pull in the fresh air and expel flue gases. So a ‘trap’ is needed to keep the furnace from pulling negative pressure on the draining of condensation and monitored by a pressure switch, a safety device.

What Do Condensation Traps Get Blocked?

Herein lies the concern- the intake pipe is always pulling air inward for combustion to happen and at the same time, moisture, dust, dirt, and leaves can be pulled in as well. This debris travels through the piping, into the combustion chamber and is mixed with the condensation. As mentioned everything drains into the ‘trap’. Over time, especially during the summer, this debris and condensation sit at the bottom of the ‘trap’ decaying, drying out, and forming an almost cement-like blockage.

Which Furnace Brands Have Condensation Traps?

All the name brand systems, Carrier, Lennox, Rheem, Amana, etc., have condensation traps. However, Carrier seems to have the biggest issues with these ‘traps’. By the same token, the only real prevention is annual maintenance as recommended by all manufacturers.

What Should I Do if My Furnace Shuts Off Randomly?

Oftentimes, when the furnace stops working, owners will begin frantically searching for a service company to get the heat back on. By the time a technician arrives, the furnace may have already started back up and running fine. This is because it has had time to drain slowly and doesn’t produce as much condensation. If it happened once, it will happen again within the same time frame.

If you get your furnace checked annually and know that there is nothing wrong with your furnace, then you may be more confident to wait until it turns on again later. However, if you suspect that it needs repair, you may need to call a furnace technician in Commerce City for help.

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If you are experiencing concerns with your furnace, call Sunshine Home Services at (303) 622-5526 or complete an online form to schedule an annual or repair heating service.


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