In this case, you'll want to check for the following: Tripped Circuit Breaker: The main issue here is not with the thermostat itself but with the electrical panel. Go to the breaker panel and locate the circuit breaker for your thermostat. If it's off, try to reset the breaker switch.
The most common reasons for a blank thermostat screen are dead batteries, a power outage, a tripped circuit breaker, faulty wiring, or a failed thermostat. The screen will be completely dark and unresponsive when there is an issue with power reaching the thermostat.
Place the multimeter's red probe onto the thermostat terminal marked R for red; you can place the black probe onto any of the other terminals. The multimeter reading should be at or close to the thermostat's voltage level.
If your furnace won't kick on when you turn the thermostat up, it could be due to a variety of reasons such as a tripped circuit breaker, a faulty thermostat, or a problem with the furnace itself like a malfunctioning igniter or gas valve. Checking these components might help you figure out the issue.
Check the circuit breaker panel.
The next simplest solution for a thermostat that has no power is a tripped circuit breaker. This is a common cause for appliances, power outlets, and HVAC equipment not working. Open your electrical panel and look for a switch that is not aligned with the rest.
Flip the circuit breaker that powers your thermostat to the 'off' position. Wait 30 seconds. Flip the circuit breaker back on. Switch the thermostat mode from 'off' to 'auto', 'fan', 'cool', or 'heat'.
When low batteries eventually die, you'll see a black display screen, the thermostat will stop working and your heating or cooling units won't function. The heating and cooling system cannot respond to nonexistent temperature commands.
There is usually a small reset button somewhere on the thermostat. Finding this button may require that the thermostat panel be removed and pressing this button may require something like a paperclip to push. Hold the reset button down for 5 seconds and the thermostat should reset.
The common wire, sometimes referred to as the c-wire, is what's responsible for delivering constant power to your thermostat. For programmable and smart thermostats, c-wires are required for setting a heating or cooling schedule.
Check the Power Source: Ensure your thermostat is receiving power. Replace batteries if your model requires them or check the circuit breaker if it's hardwired. Inspect the Wiring: Over time, wiring can degrade. Inspect for any loose connections or signs of wear.
No power: If the thermostat isn't working at all, there could be a power issue. Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
Replacing a Thermostat. You'll pay between $15 and $300 for the unit in addition to labor ($65 to $100 per hour) to replace an old thermostat with a new one.
The most obvious sign that you need to change your thermostat batteries is when the thermostat literally tells you the batteries are about to die! Most programmable models will now flash a low battery warning, usually about a month or two before the battery completely dies.
The most common reasons for a blank thermostat screen are dead batteries, a power outage, a tripped circuit breaker, faulty wiring, or a failed thermostat. The screen will be completely dark and unresponsive when there is an issue with power reaching the thermostat.
The Lifespan of a Thermostat
On average, most thermostats last about 10 years, depending on the model, usage, and proper maintenance. However, many people decide to replace their unit sooner to take advantage of new energy-saving technologies.
This can happen if there is a power surge or if the thermostat is connected to a faulty electrical circuit.
A bad transformer or bad wiring can also cause your thermostat to go blank. Another possibility is simply that the thermostat is broken and needs replacing. All thermostats reach the end of their lifespan at some point. If yours is an older one, it's a good idea to replace it with a programmable one.
If your thermostat is blank, the first thing you should do is check the batteries. Chances are, the batteries have died and the thermostat simply can't power on. Replace the batteries and see if your thermostat turns back on. Most thermostats display a low-battery symbol when the juice is running low.
A blown fuse inside your thermostat will cause the device to malfunction. You'll need to open the panel and locate the fuse. This is a small, clear cylinder with metal ends and a filament running through the center. If this filament brakes, the fuse has blown and will need replacing.
Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.