What’s The Cause Of Clicking Sound From Air Vents When Heat Is ON?

It is absolutely normal to hear a single click coming from your air vents once the heating and cooling system gets turned on. However, continuous clicking can be a sign of a bigger problem and the best thing that you can do is shut the unit down and call an HVAC expert as you might be dealing with:

  • A fan obstruction
  • A failing compressor or capacitor
  • A malfunctioning thermostat or relay switch
  • A problem within the pilot light assembly (in case you have a gas furnace)
  • Damaged ductwork

Below you will find a few tips on how to deal with the issue. In any case, you might want to start with identifying the source of the sound that you hear coming from the air vents.

What’s The Cause Of Clicking Sound From Air Vents When Heat Is ON?

If you hear a single clicking sound when the system kicks in or shuts down, then you have nothing to worry about. The click is the thermostat sending a signal to the capacitors or the ignition starting.

However, a continuously clicking system can become a reason for concern. This can mean that either the equipment is not able to turn on at all, or there is something wrong with one of the elements and it’s making the noise during operation.

No matter where the sound is coming from, you might be able to hear it from the air vents as those are connected to the air ducts that, in their turn, lead to the rest of the HVAC system.  

Read: How To Fix Insulation Blowing Out Of Air Vents?

A Fan Obstruction

One of the most common reasons for a clicking sound coming from the vents is a fan obstruction.

It’s relatively easy to find out if that’s the exact issue you’re dealing with. Pay attention to the noise. If, at first, the clicking sound is very slow, but then it ‘accelerates’, then the chances are high that the fan blades are hitting something as they are spinning.

Pretty much any foreign object that gets into the HVAC system might end up next to the fan blades. Furthermore, if the inside of the system becomes extra dirty, then the debris and dust might start interfering with the fan’s operation as well.

Sometimes, all you would have to do is clean and lubricate the fan shaft, if your furnace is producing a clicking sound.

In the most severe cases, the blades might get bent and the noise that you’ll be hearing would be the sound of the blades striking the fan casing. If the system continues running in such a case, the bent blades might cause internal damage, so it’s better to turn the equipment off and inspect the fan.

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Read: Does Closing Air Vents Help Cool Other Rooms?

Issues with the Compressor

If you have a heat pump and the source of the noise is the outside unit, then the compressor might be to blame. This component is the ‘heart’ of the HVAC system as it compresses and pumps the refrigerant.

An unsecured bolt or flexible refrigerant tubing might be causing the sound. In such a case, all you would have to do is tighten the bolts of the compressor and make sure that the tubing is securely connected.

Read: Why Dust Coming Out Of Air Vents?

Electrical Issues

The main sign of an electrical issue is an HVAC system that is producing a clicking sound but is failing to turn on.

If you hear the noise coming from the outdoor unit (you might sometimes hear it through the air vent), then it might be an indication of a failing capacitor. This element stores electricity and its main job is to provide an initial jolt of power to the motor of the HVAC system.

As the component begins to fail, it might start making a clicking sound. Start capacitors can go bad due to overheating which, in its turn, can occur because of a malfunctioning relay switch. Running capacitors can be affected by voltage irregularities and the surrounding temperature.

It is definitely an issue that should be taken care of by a professional as it involves electricity. If you think that the capacitor is the element that is producing the sound, then make sure to immediately turn the system off and wait for the arrival of an HVAC expert.

Read: Do You Have To Vent A Portable Air Conditioner In Heat Mode?

Thermostat Issues

If your air vent is located next to the thermostat, then the clicking sound might be coming from the wall-mounted device, not the actual vents.

This may be happening because:

  • The heating and cooling unit is short-cycling (this might become an issue if the air filter is dirty, the vent is blocked, or if the unit is not properly sized for the house)
  • There is something wrong with the thermostat’s wiring
  • The relay switch that has to be sending signals from the thermostat to the unit has gone bad

Read: Can An Attic Be Used To Vent A Portable Air Conditioner?

A Problem with the Pilot Light Assembly

If you have a gas furnace with a pilot light and you start hearing the clicking sound, but the unit is not turning on, then the problem might be with the pilot light assembly.

The furnace’s spark ignitor might be failing to ignite the pilot light or the burners.

In a correctly operating system, once the thermostat senses a temperature drop, the fan motor will start pulling air to the burner (at this point, the ignition system would require around a minute to energize), the gas valve with open, and the furnace burners will light.

You will hear the clicking sound if:

  • The gas valve fails to open (this might be because of a malfunctioning thermocouple)
  • There is no gas
  • The pilot flame is not hitting the flame sensor in the right place due to an incorrect air-fuel ratio
  • One of the elements of the pilot light assembly gets clogged or worn down or becomes loose 

In any case, finding the root cause of the problem might be challenging even for experienced DIYers, so it’s better to call an expert. What you can attempt to do on your own is carefully clean the pilot light.

Damaged Ductwork

If your furnace or heat pump is operating normally, but you hear a sound coming from the air vents, then you might have a loose duct or a gap somewhere in the ductwork. Such an issue can cause all sorts of sounds, including a clicking noise.

Fortunately, this is one of the problems that you might be able to solve on your own. Simply inspect the ductwork for any obvious signs of damage.

If you weren’t able to find any gaps, turn the system on, and drag a piece of toilet paper along the ductwork. If the paper starts wiggling, you would have to seal the gap with special tape or mastic sealant.

Final Thoughts

In the majority of cases, a clicking sound coming from the air vents when the heat is on indicates a big problem within the HVAC system that needs to be addressed as soon as possible. If you hear a continuous clicking noise, you have to immediately turn the unit off and call a professional. Leaving the system on can lead to extensive damage, and it doesn’t really matter whether you’re dealing with bent fan blades or an electric issue.