Honeywell Thermostat Error 89? – (Easy Fix Guide)

Is the Honeywell thermostat error 89 frustrating you? You’ve come to the right place.

You want to restore your thermostat functions to normal, but power issues likely cause this error.

The display will go blank, or no heating or cooling is coming out of your system.

To fix the error 89 from your Honeywell thermostat, you must ensure all the wires are connected properly. You also want to look at your thermostat’s settings and configure it correctly.

Let’s fix this in no time!

Honeywell Thermostat Error 89 – 8 Proven Methods to Fix

Don’t worry since we have 10 proven methods on how to fix this error with your Honeywell thermostat.

You don’t need special tools or skills if you follow the steps closely.

#1: Replace the Batteries on Your Thermostat

The first and simplest solution is to check the batteries on your thermostat.

Low or dead batteries can cause this error from a communication failure between your thermostat and the unit.

Replacing the batteries will help, and here’s how you do it:

1. Turn off the power to your thermostat.
2. Remove the thermostat from the wall.
3. Find the battery compartment.
4. Remove the old batteries.
5. Replace them with new ones.
6. Return the thermostat to the wall.
7. Turn on the power and see if the error returns or not.

Pro Tip: Always use fresh batteries when replacing them, as older ones won’t have enough power to keep your thermostat running.

#2: Power Cycle Your Thermostat

If you’re dealing with a Honeywell thermostat error code 89, it’s due to a glitch or error during a power outage or surge.

The most effective way to deal with this is by power cycling your thermostat to flush out bugs.

Follow these steps to do it:

1. Locate the power switch or breaker for your system.
2. Turn off the switch or breaker.
3. Wait for at least 30 seconds to 1 minute.
4. Turn On the switch or breaker.
5. Allow a few minutes for your thermostat to reboot.
6. Check your display for error 89.

If the error message does not appear on your thermostat’s display, it’s fixed, and you have all the functions back.

On the other hand, if it reappears, you need to look at your thermostat’s connections.

To do that, proceed to the next solution below.

#3: Check Your Thermostat’s Wiring Harness

Your Honeywell thermostat has a wiring harness that connects it to the rest of your system.

If any of these wires are loose or damaged, they will cause a communication failure, which results in this particular error.

You want to check your thermostat’s wiring and make sure they’re connected properly.

Here’s how to do it:

1. Turn off your thermostat and system through its power switch or breaker.
2. Remove your thermostat from the wall.
3. Inspect the wiring harness and look for signs of fraying, cracking, or melting.
4. If you see any damage, you need to replace the wires.
5. If you don’t find any damage, check if the cables are securely connected to terminals.
6. Replace your thermostat on the wall.
7. Restore the power and check your display for the error.

Pro Tip: It’s also a good idea to double-check the wiring colors, as it causes errors.

Wire Color	Terminal	Function
Red	R	24-volt power
White	W	Heating
Yellow	Y	Cooling
Green	G	Common
Blue	O/B	Heat/Cool Reversing
Brown	C	Common (optional)

#4: Inspect the Sensor Wire

Apart from the wires in the wiring harness of your Honeywell thermostat, there’s also a sensor wire that connects it to your system.

• It’s a thin wire responsible for transmitting temperature signals between your devices. 

If this is faulty, it will cause an issue that will display the error 89 message.

Here’s how to fix this:

1. Turn off the power to your thermostat.
2. Remove the thermostat from the wall to reveal the wiring.
3. Locate the sensor wire, a small, thin wire connected to the thermostat.
4. Disconnect the sensor wire from the thermostat.
5. Check for signs of damage, such as melting or corrosion.
6. If there’s damage to the sensor wire, replace it.
7. Return the thermostat to the wall.
8. Turn on the power to the thermostat.

Note: Ensure you get the correct replacement for your sensor wire for it to work correctly.

#5: Verify that Your Thermostat is Receiving Enough Power

With the Honeywell error 89, you must verify that your thermostat receives the right power setting. It requires a certain voltage for it to operate correctly.

If the voltage is too low or high, it will cause a failure between your thermostat and the system, resulting in an error.

To verify that your thermostat is receiving enough power, follow these steps:

1. Turn off the power of your thermostat and remove it from the wall.
2. Locate the C terminal in the wiring harness.
3. Use a multimeter to measure the voltage between the C and another terminal.
4. The multimeter should read between 18 to 30 volts AC.
5. If it’s lower or higher, there is a problem with your home’s electrical wiring.

We recommend you contact a professional technician to fix your system’s power supply to get it back up and running properly.

#6: Check Your Compressor’s Fuse

Your compressor is part of your system that helps cool or heat your home. It has a fuse that protects it from overloading or short-circuiting.

If this fuse blows, it causes a communication failure, resulting in the error 89 message.

Here’s how to check your compressor’s fuse:

1. Turn off the switch or breaker to your thermostat and system.
2. Find your compressor from outside your home.
3. Open the access panel of your compressor by unscrewing it.
4. Locate the fuse holder inside.
5. Remove the fuse by pulling it out.
6. Inspect the fuse for signs of damage, like burning, melting, or breaking.
7. If you find damage, replace the fuse with a new one of the same type.
8. If there is no damage, test it with a multimeter.
9. Close the access panel of your compressor.
10. Turn on the power to check if the error persists.

#7: Reconfigure Your Thermostat’s Settings

Your thermostat has settings that control how it regulates your system.

Whenever some of these are incorrect or incompatible, it will show the error 89 message. You want to ensure that you’re using the right configuration.

Here’s how you do it:

1. Press and hold the Menu button on your thermostat.
2. Hold it for 5 seconds until you see the Installer Setup menu.
3. Select the one that matches your system type.
4. Press the Next button to confirm your selection.
5. Configure each of the settings to match your system type.
6. Press the Done button.
7. Check your display for the error 89.

Tip: As for your system type, see the table below:

System Type	Acronym
Single-stage heating and cooling	SHC
Multi-stage heating and cooling	MHS
Heat pump	HP
Baseboard heating	BBH
Fan coil	FCU
Zoned heating and cooling	ZHC
Commercial HVAC	CH

#8: Check Your Electronic Interface Module

The Electronic Interface Module, or EIM, is a device that connects your thermostat to your system wirelessly.

It allows you to control your system using a smartphone. If your EIM is malfunctioning, it will cause this error.

Here’s how to fix this:

1. Turn off your thermostat and remove it from the wall.
2. Locate the EIM module at the back of your thermostat.
3. Inspect the EIM for damage like cracks, dents, or loose connections.
4. If you see any damage, you will need to replace it.
5. Make sure that you connect the wires properly.

Note: If you’re unsure how to replace your EIM, we recommend contacting a qualified HVAC technician to help you with more advanced methods.

These methods should help you resolve your Honeywell thermostat error 89.

If you continue to get this error, we recommend contacting Honeywell Support for a more technical solution. 

Recap

Your Honeywell thermostat error 89 means an issue with your device and system. The best way to resolve the issue is by checking your thermostat’s wiring and ensuring they’re properly connected.

You also want to look at power source problems.