Furnace Will Not Turn On With Thermostat

When people can no longer tolerate the cold weather, they rush to the thermostat for comfort. Pressing a few buttons should turn the furnace on and start a heating cycle. In a few minutes, warm air should flood the home and provide relief. It’s a reliable system used in millions of households. However, some might encounter problems such as a furnace that will not turn on with the thermostat. This can induce dread and anxiety in the middle of winter. Read on to learn more about why it happens and what can be done about it.

My Furnace Won’t Turn On With The Thermostat

This unpleasant surprise can be prevented with regular maintenance. An annual visit from professional HVAC technicians is typically scheduled in the fall to make the furnace ready for winter. They will inspect the system for signs of wear, imminent failure, safety hazards, excessive dirt, and other potential problems. By taking care of all these right away, the furnace is more likely to work as intended. If you have not gotten professional maintenance yet and the heating system refuses to turn on, then it might be due to any of the following:

Thermostat Issue

The thermostat is the command center of the entire operation. Hence, this is the logical start of all troubleshooting steps. If the commands you entered are not getting through, then the thermostat might be failing. This could occur in a number of ways.

Thermostat Settings

thermostat settings

Machines are designed to do as they are told. If they are behaving in a way that is different from what you intended, then check the settings. These may be the root of the problem. For example, the thermostat may be set to COOL or OFF. If you want the furnace to produce warm air, then set the thermostat to HEAT. The exact temperature setting also deserves a look. Perhaps this is too low to produce a discernible effect. Consider increasing this by five to ten degrees and see if that makes any difference.

Thermostat Not Receiving Power

If you checked the thermostat and found the settings to be in order, then you need to look elsewhere. Perhaps the problem lies with the power. If the thermostat has a dead battery, then you just need to insert a replacement and try again. Maybe the furnace will turn on immediately after this. If not, then you might be dealing with a faulty power circuit. Let technicians diagnose the situation and provide their professional recommendations.

Wrong Thermostat For Furnace

Keep in mind that thermostats come in different types. They will only work with compatible systems. If the unit installed does not match with the heating system’s capabilities and capacity, then you may end up with sub-optimal performance. There could even be miscommunications between the thermostat and the furnace. These could lead to frequent failures. Before making a purchase, do extensive research or consult an expert HVAC professional.

Bad Furnace Wiring

bad furnace wiring

Command signals and power are all sent through a network of wires. Over time, these wires could come loose, get frayed, or suffer other forms of damage. Bad furnace wiring may evenly sever the connection between the thermostat and the heating system. It is a common problem that deserves attention. Homeowners who are knowledgeable about wiring should check once at least a year. They could also hire technicians to come in and perform this as part of annual maintenance.

Clogged Air Filter

furnace filter

Air filters are designed to catch dirt for better indoor air quality and longer system lifespan. However, they have a limit to the amount of dirt that they can absorb. Once airflow becomes severely compromised, it’s time to replace the clogged air filter. Otherwise, the system’s efficiency and performance will drop significantly. The furnace may even shut down because of the strain. Check the filters every month and change them out when needed. Purchase compatible filters in bulk to make this easier.

Tripped Circuit Breaker

Furnaces may run on gas, propane, or heating oil but parts of the system relies on electricity. The circuit breaker protects the system from power surges and other anomalies. If the heater suddenly stopped working, then this might be the culprit. Look into all of the breakers that are connected to the system. See whether they are in good shape. You should also search for the furnace switch to check whether it is in the right position. Accidental movements could have switched this off. If so, then just bring it back to the correct setting and try again.

Furnace Belt Or Blower Problem

There are cases wherein the furnace is working but other issues might give the impression of a major problem. For example, it would be hard to ignore noise coming from the blower since this is usually high-pitched. It may simply require a fresh application of lubricant or a replacement of a worn belt. It may need a complete blower replacement. Let the professionals handle this matter to ensure a lasting and effective solution.

Check the Furnace Drain Pan

HVAC systems can reduce indoor humidity by removing moisture from the air. This collects in a drain pan and flows out automatically. However, a clog may develop anywhere along this channel and prevent proper flow. The water pump may also fail to move the liquid. This keeps the pan filled with water which may, in turn, trigger a float switch that will keep the furnace from turning on. In order to move forward, you must empty the drain pan and ensure that the water pump is working correctly.

Furnace Pilot Light

Many heating systems will not turn on if the pilot light is out. This can happen due to drafts, tripped failsafe, and system issues. Without a pilot light, furnace ignition is not possible. Relight this with a few simple steps. First, remove the access panel and look for the pilot light assembly. Turn off the reset switch and wait for 10 minutes. Come back and turn the switch to PILOT to let the fuel flow. Use a match to relight quickly. If the problem persists, then call a professional HVAC technician for assistance.

Furnace Fuel

HVAC Technician Cleaning A Natural Gas Furnace

Even if every part of the furnace is working correctly, it will not be able to produce any heat if there isn’t enough fuel coming in. The next step in the troubleshooting process is to check the gas or oil supply.

  • Heating Oil Tank or Propane Tank is Out of Fuel: Heating oil and propane are both stored around the house using tanks. Call the delivery company for a fresh refill before the fuel level goes too low. Track usage patterns to determine how much you need and when you have to get more.
  • Issues with Natural Gas Supply: If there is another appliance in the house that depends on the same fuel, then see if it still works to determine whether there is a supply issue. Examples include the stove or the water heater. Call the fuel company for assistance in case of a supply interruption.


Thermostats should be able to control heating systems without any problems. If your furnace is unresponsive no matter what you do, then go through the list above to figure out what’s going on. You can also seek the help of professional HVAC technicians to save time and effort. With their expertise, you will be able to understand the problem better and go back to normal right away.