Furnace Stops Working at Night? 8 Easy Things To Check

What can be worse than waking up in a freezing house? This is what might happen to you if your furnace stops working at night while you sleep.

The programming of the thermostat, a clogged flue, and issues with the electricity or gas supply might be to blame. It is normal for the furnace to cycle on and off up to 8 times per hour. However, it should not shut off completely when you need it the most.

Why Your Furnace Stops Working at Night

During the night, two main things are going to happen:

  1. The sun will stop heating your house
  2. Your furnace would have to work harder as the temperature drops

When the sun is shining, you might not pay any attention to the problems with your furnace as the house feels warm anyway. However, at night, when it gets much colder, the problems become noticeable.

If you have a heat pump, then the system can struggle to keep your home warm, when the temperatures drop. But this should not be the case with a furnace as such units are able to keep your space nice and toasty even on the most frigid night.

Do bear in mind that it might not be the dark time of the day that is making your furnace malfunction. Your unit may already have a persisting problem that you, as the homeowner, pay attention to only when the temperature drops.

Read: Is It Worth Getting A High Efficiency Furnace? And Why?

Why Does My Furnace Work During the Day but Not at Night?

1. an issue with the thermostat

furnace stops working at night thermostat

The first thing that you should do is check your thermostat settings. The device might have a timer that switches the system off at a certain time.

The thermostat could have been set so that it won’t allow any heat at nighttime, or is set to a much colder temperature for the night (for better sleep you should keep your bedroom relatively cool).

You can take the programming off your thermostat for a few days and try manually switching the heat on. If the problem persists, then it’s not your thermostat that’s causing the issue.

2. Tripped safety switch

Gas furnaces have a flue through which the system can get rid of the exhaust gases. If it ever gets clogged, a special safety switch will be triggered and the system will shut down.

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Taking into consideration that the outside temperatures are, in general, much colder than during the day, your flue might get clogged by ice build-up.

flue ice buildup

3. an issue with the gas line or the electricity 

The other people that live in your area or building also want to heat their homes during the cold nights. 

A large demand for electricity or gas can cause a utility-based interruption or there might not be enough gas running through the line for everyone to use.

Also, do pay attention to the small things that change during the night.

For example, if you tend to close the door to your furnace room during the night, then a pressure fluctuation and/or the difference in airflow might be the thing that is causing your unit to stop working.

If your furnace is located in an unheated and poorly isolated space and the temperatures tend to drastically drop in that room during the night, then that might be the issue.

Read: Is Furnace Exhaust Dangerous?

Oil Furnace Stops Working at Night

If you have an oil furnace, and none of the tips mentioned above had helped, then you might want to check the oil supply

During the night, the furnace will need to use more fuel to try and keep the house warm. If the oil level is too low, the unit might shut down, or sludge and sediment will get sucked into the lines.

Read: Is Furnace Condensate Toxic?

Can a Furnace Run All Night?

Even though continuously running your furnace might not be the most cost-effective way to keep your house warm, it is completely safe to leave the heating system on during the night.

If the unit is set to ‘auto’, it will cycle about 3-8 times per hour. In general, the furnace will run for around 10-20 minutes, turn off once it reaches the set temperature, and then turn back on as soon as the temperature drops.

Such cycling is completely normal during the day and night. However, if your furnace is running continuously, then there might be something wrong.

  • An excessively drafty house – in such a case, your furnace cannot reach the desired temperature simply because the heat is escaping the house and the cold outside air is entering the space.
  • A clogged filter – the furnace will be working harder (and, in some cases, longer) to draw in the right amount of air.
  • An improperly set thermostat – if the desired temperature that the furnace should reach is way too high, then the unit will never be able to have a break. Make sure to lower the set temperature, especially, during nighttime.
  • Your system is too small – the unit won’t be able to reach the desired temperature if your house is too big for the system that you have installed.

Read: Does A Furnace Use Water?

Why Does My Furnace Randomly Shut Off?

1. Restricted airflow

Check on your filter every 30 days to make sure that it’s not clogged.

dirty filter

Also, experts do not recommend closing the vents even in the rooms that don’t need to be heated.  It’s good to let at least some air run through the ducts regularly.

Otherwise, excess dust buildup can be an issue when you finally open a vent that has been closed for a long time.

Read: How Often To Change Furnace Filter?

2. A thermostat issue

Make sure that the thermostat is on and that it’s set to ‘heat’. If the device is located in direct sunlight or another heat source, you would have to find another place for the thermostat.

thermostat display

Read: Temperature Thermostat Problems

3. An improperly sized unit

A furnace that is too big for your house will end up warming up the place too fast and shutting down. It’s not really the worst problem to have, but it isn’t efficient to have an oversized HVAC system, as your system will tend to cycle on and off much more frequently.

4. A dirty flame sensor

The flame sensor can be covered in soot or be corroded. In such a case, the device won’t be able to sense the flame and your furnace will shut off. This needs to be inspected and then replaced if it is bad.

Your efficiency will suffer with a flame sensor that is not performing optimally. In fact, it may cause your furnace to stop working entirely.

furnace flame sensor

Read: Best Furnace Flame Sensors

5. A dirty blower wheel

The blades that are covered in dirt can’t correctly move the air. As a result, the unit will overheat and shut down. This can also cause the blower wheel to get out of balance. This will eventually wear out bearings and cause excessive noise and vibration.

Clean the blower wheel periodically. Any time air moves past an object, dust build-up is inevitable. Over time, it can become a real problem.

To make the point clear, just think about a ceiling paddle fan’s blades. You can see the accumulation of dust on them over a span of just a few months. Much more air than that moves past your furnace fan in that same period of time.

dirty blower wheel

How Long Should Furnace Run Before Shutting Off?

The furnace can run for 10-15 minutes before shutting off. 7-8 minutes and 20 minutes are also acceptable intervals.

Why Does My Furnace Work Intermittently?

There might be nothing to worry about if your furnace works for longer cycles at night. After all, the unit may need a bit more time to keep the house warm, once the outside temperatures drop.

However, there might be a problem, if the furnace turns on and off too frequently (short cycles).

Make sure that the airflow is sufficient, check the thermostat, and clean the flame sensor.

Read: How To Clean Gas Furnace?

Why Does My Furnace Stop Working When It Gets Really Cold?

The furnace’s workload significantly increases when the temperatures drop.

The filters will get dirty faster, the flue can get clogged by snow and ice, and loss of power or a problem with gas supply might become more frequent during the wintertime.

What Are the Signs of a Furnace Going Out?

  1. Short-cycling
  2. High utility bills
  3. Water leaks
  4. An old unit (15-20 years)
  5. A rusted flue
  6. A change of the pilot flame’s color
  7. Cold spots
  8. Strange noises
  9. Moisture buildup throughout the house
  10. Frequent service calls
  11. Health-related issues (flu-like symptoms, for example)