The thermostat may have a dead battery, so replace them with fresh ones and try again. Your furnace may turn on right away after this. If it doesn't, you may have a faulty power circuit. Have an HVAC professional diagnose this issue, and provide you with professional recommendations.
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.
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.
Check Your Thermostat: If your furnace doesn't turn on automatically, the thermostat may have lost its programming or reset. It may even simply be set on the wrong setting. For test purposes, set your thermostat about 10 degrees hotter than the current temperature to see if the system turns on.
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.
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.
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.
If nothing's happening when you're expecting the whir of a blower, check the circuit breaker and fuse. 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.
The thermostat is the central control of your HVAC system, and malfunctioning can prevent the AC and furnace from turning on.
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.
Try replacing the batteries, then check for a blown fuse or tripped breaker in the electrical panel. If the thermostat is still unresponsive, make sure the breaker is shut off and remove the cover.
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).
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.
There is usually a small reset button somewhere on the thermostat. Finding this button may require that the thermostat panel be removed and pressing this button may require something like a paperclip to push. Hold the reset button down for 5 seconds and the thermostat should reset.
The problem may be because of power, more specifically, the lack of it. The thermostat may have a dead battery, so replace them with fresh ones and try again. Your furnace may turn on right away after this. If it doesn't, you may have a faulty power circuit.
No power: If the thermostat isn't working at all, there could be a power 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.
Make sure your thermostat is set to “heat” and the temperature is high enough to turn on the furnace. Go to your electrical panel and check the circuit breaker. If it's tripped, reset it and turn the furnace back on. Check your furnace filter and if it's dirty replace it with a new one.
A clogged filter is probably the most common reason for this problem, so it's a good place to start investigating. Take a look at your filter and, if it's really dirty and clogged, it means there's restricted airflow to your furnace. This may be keeping it from being able to create heat.
The first thing to check is your thermostat. It might be clicking yet failing to trigger the heating. Ensure it's set to 'heat' mode and the temperature is above the current room temperature. Incorrect settings or a malfunctioning thermostat can be a primary reason for the furnace clicking but not turning on.
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.
Defective Igniter or Pilot Light
If it clicks but your furnace won't ignite after the combustion cycle, the electronic ignition systems probably need to be replaced. In cases where the furnace ignition starts normally but only stays on for a few minutes and then goes out, a new pilot light likely needs to be installed.
Thermostat issues are one of the most common culprits of furnace malfunctions. If your furnace isn't working as well as it should, and you've determined that other issues such as a faulty furnace heat exchanger or dirty air filters aren't to blame, you should inspect and troubleshoot your thermostat.
Clean your Air Filters, Vents, and Ducts – A clogged air filter will struggle to meet the thermostat's set temperature since the dirt and debris buildup prevents air from circulating through the vents. And as airflow into living spaces drops, so do comfort levels.