Why Do I Have a Blank Thermostat Screen?

A blank thermostat screen is scary for any homeowner, especially in the middle of winter or the heat of summer. Is it simply a matter of replacing the batteries? Is there faulty wiring somewhere? Or is it something that’s going to cost you major bucks? Maybe your whole HVAC system is broken, and you’re going to need to replace it all!

Don’t panic. If you have a blank thermostat screen, there may be a simple solution to your problem. Here are some of the most common reasons why your thermostat screen might be blank – as well as ways to fix it.

The Circuit Breaker Tripped

If the circuit breaker trips, you’ll see a blank thermostat screen. Simply reset the circuit breaker and see if that solves the problem.

The HVAC Power Is Off

Does your HVAC system have a power switch that can be turned on and off? If so, the switch should be turned to the “on” position.

The Furnace Door Is Open

Honeywell thermostats are particularly sensitive to this issue. If your furnace door isn’t fully and securely closed, the screen on your thermostat might appear blank.

The LCD Display Brightness Is Too Low

Many programmable thermostats allow you to change the brightness setting. If your settings are too low, it might seem like you have a blank thermostat screen. Some thermostats, including the most popular Honeywell thermostats, will dim the screen at a certain time (typically very early morning) to avoid burn-in. Wait and see if the screen brightens again.

The Batteries Are Dead

Some thermostats require battery power, and if the battery dies, your screen will go blank. Try changing the batteries. Clean the battery contacts with a pencil eraser and gently pry out the spring contact so you get the best connection.

Smart thermostats like the Nest use the wires connecting the heating and cooling system to recharge. But if the battery drains down, you’ll see a blank thermostat screen (or possibly a blinking light) as it recharges. Once it’s recharged itself, you’ll be good to go. If this happens on several occasions, some component of your HVAC system may be broken. The thermostat would need to use more power than usual. In this instance, have your HVAC system checked by a technician.

There’s an Electrical Issue

Faulty wiring could be the problem, especially if you’re having trouble right after installation. Thermostats from Wiser Air, for example, require a C terminal, so you might need a special wire extender. Most thermostats need a 24 VAC power supply. If the thermostat was hooked up to 120V or 240V power for any length of time, it could be damaged.

A Blown Fuse

If you blow a fuse on the furnace control board, your thermostat won’t work properly. Open your furnace control panel and check the connection between your thermostat wires. Look for a purple 3-amp or an orange 5-amp fuse on the board, and check that it’s intact. If it’s blown, you have to replace it.

A Tripped High-Limit Switch

Furnaces have high-limit switches to keep them from overheating. If your screen goes blank after several minutes of heating, it could be because the high-limit switch is tripping. This is commonly due to restricted airflow because of broken or dirty parts in the HVAC system. A failing fan motor can cause your electrical components to pull in more amperage than usual, tripping the high-limit switch. Any of these could cause a blank thermostat screen.

A Tripped Float Switch

If your drip pan fills up, it can activate a float switch which will cut power to your HVAC system. This could cause a blank thermostat screen. If you’ve tried rebooting the thermostat and changing the batteries, don’t forget to check the drain pan. Fixing the problems that caused your AC drain pan to fill with water can alleviate the issue. Refer to your manual to see if you need to reset the float switch.  

If you can’t determine the cause of your blank thermostat screen, contact Newcomb and Company. We can diagnose and fix the issue.

Need help? Call now.