Why Does My Thermostat Keep Clicking? (Find Out Now!)

It’s normal for your thermostat to click every time you call for heat (in the winter) or A/C (in the summer). However, if your thermostat is clicking constantly, it’s possible that the thermostat, thermostat wire, or relay connected to your comfort system is beginning to fail.

Before replacing any of these three components, it’s important to understand how they work with each other. Doing so allows you to better identify what’s causing the clicking sound to begin with.

A mechanical thermostat contains a bimetal coil that expands and contracts with changes in temperature. This movement causes the contacts within the thermostat to open (terminate the circuit) or close (complete the circuit).

Let’s say you set the temperature in your home to 70 degrees Fahrenheit. It’s in the middle of summer, and the thermostat registers an indoor temperature of 80°. This causes the bimetal coil to expand, pushing the contact toward a magnet which completes a circuit to your A/C unit. There’s the “click.”

If you have an older thermostat, the “clicking” is caused by the electrical contacts on a mercury bulb to fall to one side (heat) or the other (cool). Thermostats possessing temperature dials often have mercury bulbs.

Whether we’re talking about thermostats with magnets or mercury bulbs, there are a lot of moving parts that, while resilient, are prone to failure. These failures can lead to the incessant clicking you’re hearing.

Older digital thermostats contain many of the components within their mechanical counterparts. The key difference is that they use a constant flow of electricity to power the display.

For example, if you set the temperature to 70°, and the thermostat senses a temperature lower or higher than the one you’ve specified, the contacts will move accordingly. Again, there’s the click.

Note that many digital thermostats – especially the new ecobees and Nests – don’t have any mechanical components to speak of. Such products have small circuit boards (essentially, tiny computers) to register temperatures and complete electrical signals.

Clicking noises aren’t common in the new-school thermostats, even under normal operating conditions. For example, ecobee’s support team noted that a “clicking” sound may be indicative of a bad C wire, or inadequate voltage between the C and RC terminals. Always refer to the manufacturer’s instructions if attempting to install these thermostats yourself – and keep the paperwork!

If the wire needs to be replaced, go to the unit connected to the thermostat you just diagnosed. It will be an air handler if you have central air or a boiler if you have some form of hydronic heat (baseboard, radiators, and so forth).

If you have a boiler, the thermostat should either be connected to a zone valve, or a central relay, depending on the way it was originally set up. In the event you have a furnace and/or air handler, the wire will be connected directly to a circuit board mounted to the unit itself.

At this point, call a technician to figure out the best option for replacing the thermostat wire. Best option, he or she will simply snake a new line along the damaged one and connect it to your thermostat. Test the thermostat again to ensure the clicking has not returned.

All of these scenarios introduce variability. If your thermostat is placed directly near the entryway to your home, it’s constantly encountering cold gusts of air during the winter. This is especially true if the door isn’t sealed properly.

In a case such as this, the thermostat isn’t failing. It’s calling for heat or cool air like it’s supposed to. The problem is where it was installed in the home.

Even a particularly drafty inside wall can be problematic. If it wasn’t sealed properly during new construction, air may travel between the studs, throwing off the thermostat’s “true” temperature reading.

When all’s said and done, the issue may be an easy fix or a sign of something more costly. If minor troubleshooting doesn’t reveal what’s causing your thermostat to click repeatedly, the best thing to do is call an HVAC technician.

Look for someone who has experience with low-voltage. Anyone who’s installed air handlers, furnaces, A/C coils, and heat pumps should be able to figure out what’s at the heart of the issue.

If you have a boiler, get in touch with a plumber experienced in hydronic heating. It shouldn’t matter whether they’re familiar with high-efficiency or mid-range systems.

Related Questions

How can I replace my thermostat?

Replacing your thermostat may be relatively complicated or straightforward, depending on what you’re looking for.For example, if your current thermostat only needs two wires, and the one you want requires four, then you’ll have to run a new wire through your walls and back to your heating or cooling system.That’s easier said than done. Most electricians staple wires to wall studs and ceiling joists, making it impossible to snake the old ones out. In these instances, it’s worth it to call a licensed electrician to run a new wire and hook up the thermostat you want.