If you are seeing this code, you might notice your home getting uncomfortably chilly or warm because the furnace or air conditioner simply won’t kick on. You might also see a frozen screen, or hear a faint clicking sound as the thermostat tries—and fails—to engage the system. Don’t worry, though! While “memory error” sounds high-tech and scary, many times it’s just a digital “brain fart” that we can fix together with a few simple steps. We’ve got this!
| Category | Details |
|---|---|
| Difficulty | Easy to Moderate |
| Estimated Time | 20–30 Minutes |
| Tools Needed | Phillips Head Screwdriver, Fresh AA/AAA Batteries, Multimeter (optional) |
| Estimated Cost | $0 (Reset) to $150 (Replacement) |
Symptoms
Identifying Error 170 is usually straightforward because the thermostat is quite vocal about its distress. Here is what you should look for:
⚠️ Safety First: Read Before Repairing
For your safety and to avoid voiding the warranty, please check the official docs.
- The Error Display: The numbers “170” will typically flash or remain static on the digital display, often accompanied by an “Alert” or “Service” icon.
- Unresponsive Interface: You might press the “Up” or “Down” arrows or try to enter the menu, but the screen remains frozen or fails to register your touch.
- HVAC Inactivity: This is the most frustrating symptom—your heater or air conditioner stays silent, even if the ambient temperature is well past your set point.
- Flickering Screen: In some cases, the backlight may flicker or the text may appear garbled as the internal memory struggles to process the display software.
- Frequent Rebooting: The thermostat might try to restart itself repeatedly, showing the Honeywell logo and then immediately jumping back to the error screen.
What Triggers this Code?
To fix the problem, it helps to understand why your thermostat is acting up. An internal memory error isn’t usually caused by something you did; it’s typically an environmental or age-related issue.
- Voltage Spikes and Surges: This is the leading cause. If there was a recent thunderstorm or a power flicker in your neighborhood, a tiny surge of electricity could have traveled through your HVAC wiring. This surge can “scramble” the data stored on the EEPROM (the memory chip), leading to the 170 error.
- Firmware Corruption: Just like a computer or a smartphone, your Honeywell thermostat runs on software (firmware). If a background update was interrupted or if a bit of data was written incorrectly during a cycle change, the software can become “corrupt,” leaving the device unable to read its own instructions.
- Component Aging: Electronic components don’t last forever. Over many years of use, the memory cells inside the processor can simply wear out. This is more common in units that are 10+ years old. The hardware reaches a point where it can no longer “hold” the memory of your settings.
- Inconsistent Power Supply: If your C-wire (Common wire) is loose or your batteries are dying, the thermostat might be receiving “brownout” levels of power. When a computer chip doesn’t get enough steady voltage, it can throw memory errors because it doesn’t have the energy to process data accurately.
Comprehensive Repair Guide
Alright, let’s get our hands dirty (figuratively!) and fix this. Follow these steps in order, as we’ll start with the easiest fixes first.
- Perform a Hard Power Reset:
The first thing we want to do is drain all residual electricity from the unit to clear the temporary memory. Gently pull the thermostat body off its wall-mounting plate. Most Honeywell models pop right off with a firm tug. Once off, remove the batteries. Safety Tip: Go to your breaker box and flip the switch for your HVAC system to “Off.” Wait at least 10 full minutes. This allows the internal capacitors to fully discharge, essentially “rebooting” the brain of the device. After the wait, put in fresh brand-name alkaline batteries and snap the unit back on the wall, then restore power at the breaker.
- Check the Wiring and Pins:
While you have the thermostat off the wall, look at the back of the unit and the wall plate. Do you see those small gold or silver pins? They need to be straight and clean. If one is bent, use a pair of tweezers to very gently straighten it. Use your Phillips head screwdriver to ensure the wires (especially the R and C wires) are snugly tightened into their terminals. A loose connection here causes voltage fluctuations that trigger memory errors.
- The Factory Reset Sequence:
If the error persists, we need to perform a deep factory reset. For many Honeywell models (like the T-Series), you press and hold the “Menu” button for 5 seconds. Use the arrows to scroll to “Reset” and select “Factory.” Warning: This will erase all your custom schedules and WiFi settings, but it is often the only way to clear a corrupted memory sector. You’ll have to set up your thermostat like it’s brand new once this is done.
- Voltage Testing (Advanced):
If you have a multimeter, set it to AC Voltage. Touch one probe to the “R” wire and the other to the “C” wire. You should see a reading between 24V and 28V. If the reading is lower (like 18V or 20V), your transformer is failing, providing “dirty power” that is confusing the thermostat’s memory. If the voltage is steady and the error 170 remains after a factory reset, the internal hardware is likely damaged beyond repair, and it’s time to treat yourself to a new, upgraded model.
How to Prevent Error 170
Once you’ve got your home back to a comfortable temperature, let’s make sure this pesky code doesn’t come back to haunt you!
- Install an HVAC Surge Protector: Most people protect their TVs, but forget their expensive HVAC systems. You can have a technician install a dedicated surge protector at the outdoor condenser or the indoor air handler. This shields the sensitive electronics in your thermostat from those nasty power spikes.
- Annual Battery Replacement: Don’t wait for the “Low Battery” light to come on. Make it a habit to change your thermostat batteries every year—perhaps on New Year’s Day or when you change your clocks for Daylight Savings. Fresh batteries provide the consistent voltage the memory chip needs to stay healthy.
- Keep it Clean and Dry: Dust and moisture are the enemies of circuit boards. Use a can of compressed air once a year to blow out any dust that has settled behind the thermostat faceplate. If your thermostat is near a bathroom with high humidity, consider moving it or using an exhaust fan to prevent moisture from corroding the internal memory paths.
FAQ
Frequently Asked Questions
Q: Can I just ignore Error 170 if my heat is still working?
A: It is highly unlikely your system will continue to work correctly with this code. Even if it seems okay now, Error 170 indicates the “logic” of the device is compromised. It could potentially turn your heater on and leave it on, leading to dangerous overheating or a massive utility bill. It’s best to address it immediately.
Q: My thermostat is only two years old; why is the memory failing?
A: Modern electronics are sensitive. A single nearby lightning strike or a transformer blow-out down the street can send enough of a “jitter” through your home’s lines to glitch a chip. It doesn’t necessarily mean the unit is poor quality; it’s often just a result of an unstable power grid.
Q: Is Error 170 covered under Honeywell’s warranty?
A: Yes, in many cases! Honeywell (now Resideo) typically offers a 1 to 5-year warranty depending on the model. If your unit is relatively new and the “Hard Reset” didn’t work, contact their customer support with your model number and date of installation. They may send you a replacement for free.