In the winter, a furnace that doesn’t stay on is a frustrating problem that usually requires immediate professional attention. Called “short-cycling,” this problem shows up by your system turning on, heating up for a few minutes or seconds, and then turning back off before your home reaches the target temperature. So, why won’t your furnace stay running and why won’t your burner stay lit? Here are five potential issues causing your furnace to stop heating before it’s supposed to.
1. A bad thermocouple
The thermocouple in your furnace is a heat sensor installed next to the pilot light. Its purpose is to close the gas valve if the pilot light goes out, so gas doesn’t fill your home and cause a dangerous and potentially deadly situation. A malfunctioning thermocouple may lose the ability to sense heat from the pilot light, causing it to stop the flow of gas randomly. Knowing this, check the pilot light if your furnace won’t stay on. If it’s not staying lit, a bad thermocouple is the likely culprit.
2. A malfunctioning thermostat
A short-cycling furnace could mean that your thermostat isn’t calibrated correctly. This means that your thermostat is telling your heater that it has reached the desired temperature before it actually has. As a result, your system is turning off after only running for a short time. An easy test is to purchase a basic thermostat and replace yours with it temporarily. If the short-cycling problem continues, your thermostat isn’t the problem (and you can return the test thermostat).
3. A full condensation pan or a broken pump
Condensing furnaces generate condensation, which drips into a pan and then drains away by force of gravity or via a pump. However, if your furnace’s drain is clogged, the pan will begin to fill up. When the rising water reaches the full-pan sensor, your heating system automatically turns off to prevent a spill. You can easily check the condensation pan. If it’s full, then either the drain is clogged, or your condensation pump isn’t working properly.
For a clogged drain, insert a straightened wire clothes hanger to clear out the clog. We also recommend pouring an algaecide or bleach solution down the drain regularly to prevent future drain clogs. Likewise, checking your condensation pump’s condition is easy. First, check to make sure it isn’t unplugged or that a breaker hasn’t tripped. If the unit has power, inspect the hose leading from the pump for clogs. If you find any (or the hose is full of water), turn off the power to the pump, disconnect the hose, and use your trusty wire hanger to clean it out.
4. The blower motor isn’t running
This is another straightforward check. Simply put your hand over a supply register when your furnace is running. If you can feel hot air coming from the vent, your furnace’s blower motor is operating normally. If you don’t feel hot air, the blower isn’t moving air well (or at all), and your furnace is turning itself off to prevent its heat exchanger from overheating. The motor’s fan relay could have failed, or the blower motor belt might be worn out. A non-working blower motor requires immediate professional attention.
5. An air flow restriction
If the air flow to and from your furnace is less than ideal, it will overheat, then turn off to cool down, then reignite. If not addressed, an air flow restriction will cause your furnace’s high limit control switch to fail. A dirty furnace filter is the most common cause of an air flow restriction. We recommend that you change your filters regularly – at least every other month, or more often if you have pets. Blocked or closed registers are another common cause. Contrary to popular belief, closing the vents in unused areas of your home won’t save you money or ease the load on your heating system. Closing vents will create an air distribution imbalance and cause your furnace’s air pressure switch to shut the unit down to prevent damage.
If you have reviewed all five of the potential issues above and your furnace is still short-cycling, you likely have a more significant problem that needs to be taken care of by our friendly expert technicians right away. Call us today – we’re always happy to help! That’s how neighbors should treat neighbors!™