Why Does My Thermostat Click after I Turn It Off?
Ever notice a clicking sound coming from your thermostat after turning it off? This is a common issue that can be attributed to a few different causes. Understanding these causes can help you identify if the clicking is normal or if it might indicate a need for professional attention.
Relay Switch
The relay switch is a common culprit for the clicking sound. Many thermostats use a relay switch to control the heating, ventilation, and air conditioning (HVAC) system. When you turn off the thermostat, the relay may click as it opens or closes, stopping the flow of electricity to the heating or cooling system. This is a normal part of the system's operation and usually indicates that the electricity to the HVAC system has been cut off.
Expansion and Contraction
In some cases, the clicking sound you hear can be attributed to the expansion and contraction of materials in your thermostat. This is more common in older homes or systems where the thermostat is mounted on a wall that experiences temperature changes. As the materials expand and contract, they can make a clicking noise. This is typically not a cause for concern, but if the sound is loud, persistent, or accompanied by other issues, it might be worth having a professional take a look.
Mechanical Components
If your thermostat is a mechanical one, it may have internal components that click as they disengage when you turn the unit off. Like the relay switch, this clicking is usually a normal part of the system's operation. Mechanical thermostats often use a bell or other mechanism that can make a clicking sound as they operate.
System Shutdown
The HVAC system itself may produce a clicking noise during its shutdown process. This is particularly common when the system is cycling off. Some systems are designed to make a clicking sound during this process, which is perfectly normal. However, if the sound is loud, persistent, or along with other issues, it may be a sign that there is an underlying problem with the thermostat or the HVAC system.
The Click of Contacts
The clicking sound you hear is often the set of contacts inside the thermostat either opening or closing. When you turn off the thermostat, the contacts open the circuit, stopping the flow of electricity. When you turn it on, the contacts close the circuit, allowing electricity to flow and activate the HVAC system.
Older vs. Newer Thermostats
With newer thermostats, the clicking sound is more pronounced due to the use of electronic relays. Older thermostats, such as the Honeywell T87, utilized a Mercury bulb to operate the heating and cooling equipment, making the process silent. In contrast, newer electronic thermostats operate via relays, which are essentially electrically powered switches. A low control voltage on the thermostat powers the coil side of the relay, and the load side of the relay makes or breaks your HVAC control voltage, typically 24 Volts AC for various devices like fans, compressors, valves, and pumps.
Depending on the season and your HVAC configuration, you may hear several clicks. For example, when a call for cooling is made, one relay controls the compressor while another controls the indoor fan. Sometimes, some systems run the fan for a short period after the compressor stops for increased energy efficiency. Therefore, when a call for cooling ends, you may hear a click of the relay when the compressor shuts off, followed by another click 30 to 60 seconds later when the fan is turned off.
Conclusion: While the clicking sound your thermostat makes after you turn it off may be nothing to worry about, if it is loud, persistent, or accompanied by other issues, it may be a good idea to consult a professional to ensure there are no underlying problems with your thermostat or HVAC system.