Sounds like a simple enough question, no? How do I get my furnace to do what I paid it to do?
How do I motivate this furnace to ‘kick on’ and do its job?
You could try talking to your furnace but that probably won’t work.
Your furnace not kicking on could be caused by a few different factors, some of them mild and easily fixable and others, well not so easily fixable.
Let’s start with the easy, fixable stuff.
If you are reluctant to call a professional HVAC technician, there is some home troubleshooting you can do on your own.
The first step is to check the thermostat to make sure it is set to “heating” and that it’s also set high enough to warrant kicking on. If the thermostat says “fan” then make sure you change it to heating. This is a commonly forgotten step in the winter.
Isn’t funny how every summer, we forget Winter is Coming?
You could also try turning your temperature setting higher (by 5 degrees or more) to see if that triggers the furnace to kick on.
Dirty Air Filter
A dirty or clogged air filter can cause a furnace to shut off. Air filters need to be cleaned routinely for your furnace to run efficiently.
BEFORE YOU START CHANGING THE AIR FILTER, be sure to turn off your furnace’s shut off switch (right on the furnace itself) and set the thermostat to off.
Regular air filter replacement is essential to keep your furnace running efficiently full the full term of its life span (usually 15-20 years for a well-made quality furnace).
Power Supply Issues
Electric or gas, the furnace still needs the power to operate. 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”.
Is the little red light on the furnace’s circuit board on? Most modern furnaces have an indicator light to tell you it is getting power.
If the furnace still won’t kick on, it could be caused by a blown circuit breaker or its associated wires having been chewed through by rodents or corroding. This is more involved service work and better handled by a Professional HVAC Technician.
No Gas Supply
Your furnace needs gas to operate, much like many other home appliances.
Check your fuel supply by testing another gas appliance in your home, such as your stove. If it doesn’t work either, you may need to contact your gas company to resolve the issue.
If your home has gas service, it is possible the gas valve is not turned fully on, so the furnace has a sufficient supply to fire up the system.
Oftentimes, the furnace does not kick on because the homeowner thought that the valve should only be partially turned for safety reasons. The valve should be either all the way on or all the way off (this is one reason why many manufacturers have switched to switches and buttons).
No Pilot Light
For older furnace systems that operate with a traditional pilot light, you will need to check underneath the furnace to make sure the blue pilot light is lit.
A pilot light being out is quite a common occurrence that can be remedied with the strike of a match.
And now the hard stuff that an experienced HVAC technician is better suited to handle:
Blower Motor Issues
There should be an inspection window on your furnace, but that does little if you don’t know what to look for. A flashing green light indicates a working blower system, but if it is red or not blinking, there are issues. An experienced HVAC technician is best suited to inspect the motor, control board, transformer, and other components that may have malfunctioned.
There is a condensation pan on the furnace that collects excess water and if the reservoir is full the furnace won’t turn on.
Simply draining the pan isn’t a viable solution (but could work temporarily) because it doesn’t fix the issues causing this. There could be blockages preventing the water from draining or the condensation removal pump may have gone bad. An experienced HVAC technician is most capable of diagnosing this issue and performing the necessary repairs.