Thermostat Clicks, but the Furnace Doesn't Turn On

The Thermostat Clicks, but the Furnace Doesn’t Turn On – What to Do

Once the summer is gone, you probably turn on the furnace to keep your home nice and warm. You want the house to have a comfortable temperature when you come home after a busy day at work. The last thing you want is to come back to a house feeling freezing or incredibly hot. Even though you hear the furnace clicking, the furnace doesn’t turn on and doesn’t heat your house.

Many HVAC technicians get calls from homeowners with thermostats that click, but the furnace doesn’t turn on. The thermostat will click, but nothing will happen after that sound.

The thermostat clicks, but the furnace won’t turn on. What’s the problem?

More often than not, we discover that there’s a problem with the furnace after we turn it on. We should start by highlighting that there are ways to prevent this sort of problem. Sticking to a maintenance schedule with certified HVAC technicians reduces the risk of issues with your furnace.

Having said that, we present you the most common reasons why the furnace might not turn on, even after the thermostat sends the command for heating.

There’s something wrong with the thermostat

One of the first things to check out when the furnace doesn’t start, even though you hear the thermostat clicking, is the thermostat. For some reason, something could be wrong with the thermostat. A lack of power could be why you only need to replace the batteries. However, it can also be a complex issue with the thermostat. Replacing the thermostat could be the only solution.

Digital thermostats are available and the manufacturers provide customers with guides for troubleshooting the devices. Sometimes, an improper setting could be the only reason why the thermostat clicks, but the furnace doesn’t start. You need to check out if you’ve set the correct temperature. The thermostat should be on the Heat seating, not Off or Cool and the fan should be on “Auto” or “On” for proper airflow into the room.

Remember that the furnace will only start to heat if you set the ideal temperature to warm the room. Check the temperature settings and make the necessary adjustments to see if the room will begin warming. There will be no warming activity when the room’s temperature is the same as the system’s. As a result, the furnace won’t turn on. See that the other settings are also appropriate for the efficient performance of the furnace.

Another cause for the furnace not starting even when the thermostat clicks are using the wrong thermostat for the furnace. The thermostat should match the furnace when it comes to capacity and ability. When you set the faulty thermostat for the system, there could be miscommunication between the thermostat and the system. The system could fail, so ensure you always have a thermostat compatible with your furnace.

The air filter is clogged

Another common issue for furnaces and air conditioning units is the clogged air filter. When you turn on the furnace, but it doesn’t start heating or doesn’t blow hot air, the filter could be clogged. It happens because dirt and dust build up on the filter, decreasing airflow throughout the system and making the furnace shut down.

Check out the air filter when the thermostat clicks, but the furnace doesn’t turn on. Cleaning the air filter is relatively straightforward, but filters will need replacing after some time. Buy the air filter according to the size of your furnace.

If the filter is clogged, we recommend you check the whole system. Soot might have gone into the system due to the clogged filter. When the air filter is clogged, the furnace can malfunction in many ways, with the thermostat clicking without the furnace heating. Ideally, you should replace the furnace filter every three months or at the beginning of every season.

The furnace’s performance will decline when you don’t clean or replace the filter whenever necessary—a furnace filter costs around $5, much less than a new furnace.

The wiring is bad

Frayed wires, loose connections, and old wires can make the thermostat lose its connection to the furnace. Check out the wiring carefully and see that all connections are tight. Replace wires if necessary, or contact an HVAC technician to do it for you.

The breaker has tripped

Sometimes, for various reasons, the circuit breaker to the heater may trip and turn off the furnace. Check out all the breakers and see that their condition is fine. Additionally, the furnace comes with a switch that turns the furnace off. It happens because of a problem and might have been switched off by accident. Make sure that nobody turns the furnace off for a specific reason.

There’s a problem with the blower or the belt

Sometimes, there’s nothing wrong with the furnace, but the blower isn’t performing as expected. When you hear sounds coming from the furnace (high-pitched ones), the blower might be damaged. If so, you should take it to the professionals and have an HVAC technician examine and fix the furnace. Sometimes, the belt could be dry and require oiling, or it’s worn out and needs replacing.

Replacing the motor or the blower can be expensive, which makes the maintenance routine even more important than you think.

The pilot ignitor is defective

Take a look at the pilot ignitor when you hear the thermostat clicking, but the thermostat doesn’t start to heat the air. Gas furnaces are sensitive to dust, debris, and dirt that can deposit on the pilot igniter. Sometimes, you only need to clean the pilot ignitor. You will need to replace it if it’s cracked or damaged.

Use a brush and compressed air to clean the pilot light. Use the brush to clear away debris and blast it with air to remove the deeply set dust. The pilot ignitor will be clean and able to run the furnace whenever the command for heat comes from the thermostat.

The capacitor isn’t in good shape

A defective capacitor can also make the furnace not start even if it receives a command for heating from the thermostat. The capacitor stores the electrical charge that the furnace uses to turn on the compressor; its role is similar to a battery’s.

If the capacitor is faulty, you should notice a buzzing sound after the thermostat clicks. The sound informs that the compressor is starting, but there’s no charge from the capacitor. It’s not a problem to solve on your own. You do have a clue that the capacitor is faulty, so you can help the HVAC technician when he comes to handle it.

We want to warn you that the capacitor has stored voltage and can cause shocks when you mishandle it.

The gas line is disconnected

Gas furnaces won’t run when the gas line is disconnected. Even if you adjust the thermostat, the furnace won’t start to heat when there’s no gas connection. Turn the furnace off so that you safely check out the gas lines.

You can reattach the gas lines if you don’t see any damage. In time, the gas lines can become loose even if the connection wasn’t tight initially. Call the emergency services immediately if you notice a gas leak near the furnace’s gas line. It’s a fire hazard you cannot overlook.

Gas furnaces cannot run without gas and the gas valves should be opened, especially if the thermostat clicks and the furnace doesn’t heat. You should turn it on slowly and notice if the furnace begins to start.

Other causes

When the thermostat clicks and there’s no heat coming, a frayed wire or an electrical problem that it’s tricky to diagnose could be the cause. The furnace doesn’t break easily.  Should that be the case with your furnace, other signs will tell you it’s time to go shopping for a new unit.

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