There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.
If your furnace won't kick on when you turn the thermostat up, it could be due to a variety of reasons such as a tripped circuit breaker, a faulty thermostat, or a problem with the furnace itself like a malfunctioning igniter or gas valve. Checking these components might help you figure out the issue.
One of the most common reasons why thermostats don't work is dead batteries. If the batteries your the thermostat are dead, the thermostat will not be functional. Therefore, you will need to replace its batteries. If the thermostat still does not work after you do this, you may need to call a professional for help.
If the batteries in a thermostat are almost dead, it can cause the thermostat to malfunction, which may result in the furnace not working properly (1). The thermostat relies on power to regulate the temperature and communicate with the furnace, so low or dead batteries can disrupt its functioning.
Possible causes include a broken thermostat; the thermostat being set too low; an out pilot light; a blown fuse or circuit breaker; a closed gas valve; or electronic ignition problems.
If your boiler stops responding to your thermostat or heating controls, it's worth checking the batteries. Not all thermostats use batteries - some are wired into the mains but have backup batteries in case your power fails. If you've experienced a power cut, your thermostat's backup battery might've run out.
Checking your thermostat is the best place to start. Make sure it's set to “heat” and that you've set the temperature higher than the current room temperature. If that doesn't resolve the problem, try switching your fan to “on” to force the furnace to start working.
If your thermostat is fully functional and you're still unable to feel any heat coming from the vents, you may be dealing with some of these problems: Dirty evaporator coils. Clogged pipes. Full air filters.
There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.
Furnace Not Igniting Because of Incorrect Thermostat Setting
Make sure the thermostat is set to heating and that the temperature is set high enough to actually turn the furnace on. It may be set at too low of a temperature to activate the furnace.
The cause of your furnace not blowing hot air could be the thermostat configuration, a dirty air filter, the high limit switch, a clogged condensate line, insufficient fuel, leaky ducts, ignition problems, a blocked burner, flame sensor issues, gas valve malfunctions, a cracked heat exchanger, or a clogged coil.
Look for loose wires or relay connections that you can tighten. Or, turn off the breaker to the unit, wait a couple of minutes, and turn it on again (or reset the breaker if it has tripped). The thermostat should start working; if not, it may need to be replaced.
Check the configuration of the thermostat to make sure it is controlling the equipment properly. Verify that the thermostat is wired correctly. Make sure all of the wires are secure and in the correct terminals. Make sure the voltages are between 18 and 30 VAC or 20 and 30 VAC depending on the thermostat model.
At your electrical panel, make sure all switches related to the HVAC system are on. Reset any tripped breakers and replace all blown fuses, and your furnace should kick back on. Gas supply leaks: If you smell gas, leave the area immediately and contact your gas company for emergency services.
Faulty Wiring or Equipment: Bad wiring can prevent power from reaching your thermostat. It can also increase the risk of a short circuit or fire. Check whether the thermostat's wiring is frayed, broken, or installed incorrectly (the wires/terminals are usually color-coded).
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
Check the Power Source Sometimes the problem between the thermostat and your furnace is as simple as replacing the batteries. Many digital thermostats use standard batteries to power their functions. Also make sure to check there is power at the furnace as well.
It Won't Turn On
Check your breaker box for a blown breaker or tripped fuse. You may be able to fix this AC issue with the flip of a switch. If that doesn't do the trick, check the wiring in your thermostat. A loose or frayed wire could also prevent your unit from turning on.
So, if your furnace is failing to ignite, it's a good idea to check the air filter. If it looks clogged up, then this is probably the source of the problem. Change the air filter and see if your ignitor will then begin to work again. If not, then this isn't the cause of the issue.
Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires. If you spot any problems, contact an HVAC technician for assistance.
If your furnace doesn't switch on, the circuit breaker could be shut off. Check your circuit breaker panel to make sure all switches for your HVAC system are set to “ON.” Check Your Thermostat: If your furnace doesn't turn on automatically, the thermostat may have lost its programming or reset.
If your furnace's problems continue, contact an HVAC expert. Also, if you notice discoloration when you check the pilot light, get professional help. If there are cold spots in your home, even though hot air is coming out of the air vents, the issue could be different from your furnace not working.
If your thermostat won't turn on the heat in your home, change out the batteries and see if that fixes the problem. If not, your faulty thermostat could be the result of the following: A tripped breaker. Loose wiring.
If your heater doesn't start, chances are the problem stems from having a dirty furnace. Having dirt on your blower motor or flamer sensor could render your furnace unable to perform. When the blower motor is too dirty, it won't pass enough cool air to the heat exchanger, leading to equipment failure.