Honeywell Thermostat Error Codes List: Every Alert Code Explained

Every Honeywell thermostat error code we could verify against Honeywell's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.

How to read and retrieve error codes on Honeywell thermostats

On T-series models an active alert puts the alert icon on the home screen (on the T6 Pro Z-Wave, the alert symbol and the alert NUMBER appear in the clock area). The full report lives behind Menu > ALERTS on touchscreen models — Menu > ALRT, then Select, on the button-style T6 Pro — where each alert shows its 3-digit code and its definition, and multiple alerts are paged through with the arrow keys. The same alerts are manageable in the Resideo app (select the thermostat, Settings, Manage Alerts) on connected models. VisionPRO 8000 (RedLINK) announces alerts differently: a red alert light and a plain-text message on screen — there is no numeric table to look up, the message is the diagnosis. VisionPRO IAQ hides its codes one layer deeper: an 'Err' in the time field of the home screen means the thermostat has detected an error on the communication bus, the code itself is read in the manual's Table 14 system (and via diagnostic recall), and the EIM's communication LED gives the bus's own verdict — rapid blinking is normal transfer, continuous blinking or always-off is a wiring problem, always-on means the EIM may need replacement. Practical rule across all lines: photograph the alert screen before dismissing anything — a dismissed reminder restarts its timer, and a fault alert that clears when its cause clears leaves no owner-visible history behind.

The complete Honeywell thermostat error code list

How to reset / clear error codes on Honeywell thermostats

Honeywell alerts do not clear like appliance fault codes, and the T-series splits them by kind. Maintenance reminders (181-189) are timers, and clearing one IS resetting its timer: on touchscreen models, replace/clean the item first, then touch 'Dismiss' on the alert screen — Resideo's table wording for every reminder is 'Reset the timer by touching the dismiss button after it is replaced'; on the button-style T6 Pro, press Menu, step to ALRT, press Select, then either snooze (SNZE, 7 days) or clear (CLER). Resideo's caution heads both flows: some alerts cannot be snoozed or cleared — those are the fault alerts (164, 168, 170, 173, 177, 178), which clear only when their cause is fixed or the dealer replaces the failed part, and Resideo's instruction when an alert will not clear is to call your heating and cooling professional. Informational alerts (171, 175, 210, 388) clear by doing the small thing they ask (set the clock, register the thermostat) or, for 175, by simply being read — power already resumed. VisionPRO 8000 (RedLINK) works the same way in words instead of numbers: Dismiss clears the alert message and turns off the red alert light, and each IAQ reminder has a Reset Timer control. VisionPRO IAQ error codes are diagnostic reports on a communicating system; they clear when the underlying condition (a failed sensor, a duplicate device, a silent bus) is corrected by the installer. No Honeywell platform here has a 'clear all codes' owner button, and a power cycle re-reports any standing fault rather than clearing it.

How to diagnose any Honeywell thermostat code

Work the problem in this order: (1) write the code down exactly, including its letter prefix — on a smart thermostat the prefix names the family (a power report, a wiring report, a connection report), and the family matters more than the number; (2) remember what the thermostat is: a witness, not the patient. Most thermostat codes report the heating/cooling equipment — a furnace that lost power, a float switch that tripped, a wire that is not seated — so the second stop is always the equipment itself: is its power switch on, its breaker untripped, its access panel fully closed (the panel switch kills power on many furnaces), its condensate drain clear; (3) check the wiring at the thermostat base with the equipment powered OFF — a wire pushed beside its terminal instead of into it is the classic cause of wire-not-detected codes; (4) restore power and let the thermostat re-read the system before judging the result, because power codes clear only when the equipment actually delivers power again; (5) if the equipment runs normally from its own test mode but the thermostat still reports the fault, the wiring run or the thermostat itself is the remaining suspect — and 24V wiring faults inside walls or at the equipment board are a technician's job.

Honeywell's numeric alert system is real — and the 'E1 to E5' tables all over the internet are not

Search 'Honeywell thermostat error codes' and the top results will confidently explain E1, E2, E3, E4 and E5 — a sensor error, a memory error, a power error, neat as you like. Now open the manuals Resideo actually publishes for the current Honeywell Home lines — the Lyric T6 Pro Wi-Fi user guide, the T6 Pro Smart user guide, the T6 Pro Z-Wave install guide (33-00294-03), the Lyric T6 guide (33-00170E-01), the VisionPRO 8000 with RedLINK manual (68-0312-01), the VisionPRO IAQ manual (68-0287-04) — and search them for an E-code. There isn't one. Not a single E-prefixed alert appears in any of them. What the manuals contain instead are two genuinely different numeric systems and one system with no numbers at all, and keeping them apart is the whole skill of reading a Honeywell display. The T-series system (T5, T6 Pro, Lyric T6 Pro Wi-Fi, T6 Pro Smart, T6 Pro Z-Wave) uses three-digit alert numbers in the 54-508 range: service faults in the 160s and 170s (164 heat pump needs service, 168 Wi-Fi radio error, 170 internal memory error, 173 thermostat sensor error, 177/178 wired sensor errors), maintenance timers at 181-189, an informational power notice at 175, registration prompts at 210 and 388, and connection reports at 399, 400 and 508. Even inside this one family the membership moves: the Z-Wave model drops the Wi-Fi-only codes and adds its own (252 AC power lost, 546/547 for its Z-Wave radio, 405/407 for its batteries), because the table belongs to the model's feature set, not to the brand. The VisionPRO IAQ (TH9421C) system is a different dialect entirely — two- and three-digit error codes (027, 035-040, 050-054, 089-091, 118, 119, 121) that describe a communicating system of thermostat, Equipment Interface Module and zoned devices: duplicates on the bus, faulty discharge and outdoor sensors, equipment gone missing from the data interface. Its numbers must never be read with the T-series table, and the T-series numbers mean nothing on an IAQ display. The confusion is understandable because the IAQ world also uses look-alike numbers for installer setup — but those are four-digit (0172 system type, 0670 keypad lockout), while the error codes are the short ones that appear after 'Err' in the time field. And the VisionPRO 8000 with RedLINK skips numbers altogether: alerts are plain-text messages beside a red alert light, cleared with Dismiss. So where do the E-tables come from? Other brands' systems genuinely do use E-codes — Nest's help codes are the famous example — and content sites copy a plausible table from one brand's pages onto every other brand's, pad it with generic causes ('check wiring, reset, call support'), and rank. The tell is always the same: no manual, no document number, no model scope. A real Honeywell code can be pointed to, in a named Resideo document, with a definition in Resideo's own words — every code on this page can. Quote the number AND the model when you search or call: '173 on a T6 Pro Smart' is a diagnosis; 'E3 on a Honeywell' is a rumour.

Maintenance reminders vs real faults: which Honeywell alerts are timers, which are failures, and why they clear differently

A Honeywell T-series alert list mixes two species that look identical on screen and behave oppositely, and telling them apart is worth real money — one species wants a fifteen-minute chore, the other wants a dealer, and treating either as the other wastes both. The reminders are 181 through 189: replace air filter (1) and (2), clean the humidifier tank and water filter, replace the humidifier pad, replace the dehumidifier filter, clean the ventilator core, clean or replace the ventilator filter, replace UV bulb (1) and (2). Every one of them is a timer, not a measurement. The thermostat does not sense a dirty filter, a scaled pad or a faded UV lamp; it counts run-time or calendar days against an interval the installer set, and announces that the interval expired. That is why Resideo's definition for each is a two-step instruction — do the maintenance, then 'reset the timer by touching the dismiss button' — and why dismissing without doing the work is self-defeating: you have not cleared a warning, you have restarted a countdown that will expire again in a filter's lifetime whether or not a filter was ever changed. The button-style T6 Pro makes the same distinction tactile: reminders can be snoozed for 7 days (SNZE) or cleared (CLER) from Menu > ALRT, which is the system trusting you that the work is done or scheduled. The faults are the other species: 164 (heat pump needs service), 168 (Wi-Fi radio error), 170 (internal memory error), 173 (thermostat temperature sensor error), 177 and 178 (wired indoor/outdoor sensor errors), and on the VisionPRO IAQ line the sensor, duplicate and communication errors. These are measurements and self-tests reporting a present condition, and Resideo's definitions for them end with the same phrase — 'contact dealer' — because there is no dismiss path that fixes a failed sensor: the alert clears when the condition clears, which usually means a part or a wiring fault was repaired. The platform even encodes the difference in behaviour: Resideo notes that some alerts cannot be snoozed or cleared, and if you meet one, the system may require service — an un-dismissible alert is the thermostat telling you which species you are holding. Between the two species sit the notices that are neither: 171 (set the date and time), 175 (AC power resumed — an event log), and the registration/connection prompts 210, 388, 399, 400 and 508, which ask for a small administrative act — set a clock, register in the app, restore a network — and then go away on their own. The owner's rule of thumb is simple: 18x means schedule the chore and then dismiss; a 16x/17x fault means the chore is a phone call; and if an alert refuses your Dismiss, believe it — you have misread which species it is.

The most searched Honeywell thermostat codes, in detail

175 — AC power resumed

Alert 175 is the odd one out in the Honeywell T-series table: it is not a fault, a reminder or a request — it is the thermostat logging an event that already ended. While power was gone, the thermostat could show nothing at all (a C-wire-powered model goes dark with the system; a battery-backed model rides the outage out on its batteries). When AC power returns, the thermostat restarts, notes that power was lost and restored, and files 175 in its alert list so the gap in operation is explained rather than mysterious. One normal behaviour follows it and is often mistaken for a second fault: heating or cooling does not restart instantly. Resideo documents a built-in compressor protection feature that prevents the compressor from restarting too soon after a shutdown, and states explicitly that this startup delay also applies after AC power loss — on the button-style T6 Pro the same protection shows as 'Cool On' or 'Heat On' flashing, and the manual's instruction is to wait 5 minutes for the system to restart safely, without damaging the compressor. The alert itself may sit in Menu > Alerts until you look at it; it is information, not a block. What 175 cannot tell you is why the power went away: a neighbourhood outage, a tripped breaker you reset, someone switching the system off at its power switch for other work, and a furnace door left ajar after a filter change all produce the same single line in the alert list. A single 175 after a storm is the end of the story. A 175 that keeps coming back, with no outage to explain it, is the thermostat witnessing an intermittent power problem — and then the alert stops being trivia and becomes the evidence.

Most likely cause: A utility power outage that has ended — The textbook 175: the grid dropped, the system lost its 24 VAC supply with everything else in the house, and power came back. The thermostat's wording — 'restored after a power failure' — assumes exactly this story, and Resideo's instruction for it is no action.

First check: Read the alert properly first: Menu > ALERTS (touchscreen models) or Menu, then +/− to ALRT, then Select (button models). If 175 is the only alert and the system is heating or cooling normally, Resideo's guidance is that no action is needed — note the date and move on.

If it keeps coming back: A returning 175 is the whole diagnostic content of this code. Read the pattern before the part: returns that match storms or neighbourhood flickers are the grid's story and end when the grid settles. Returns with no house-wide witnesses — the microwave clock keeps time while the thermostat logs outages — localise the loss to the HVAC power chain: a door switch that opens under blower vibration after a filter change, a system switch with a failing contact, a breaker weakening toward repeated trips, or a 24 VAC supply that sags under load. Each return also restarts the compressor-protection delay, so a system losing power several times a day spends its life waiting to restart and never quite heating or cooling — that comfort complaint, plus the log of 175s, is what to hand the technician.

Less common and model-specific codes

Search data shows owners also meet these codes on Honeywell thermostats: 051. They are not part of the core code list Honeywell publishes for most models — several are series-specific, abbreviated display readings, or codes carried over from a sister platform — so we do not publish meanings for them rather than guess. Treat them by symptom: note what the machine was doing when the code appeared (filling, draining, heating, spinning), run one full power cycle (5 minutes off), and if the code returns, match the symptom to the closest documented family in the table above and check the tech sheet stored inside your machine for the model-specific definition.

Deep-dive guides for the most searched codes

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Facts on this page were checked against manufacturer documentation: manuals.plus · cdn-cms.f-static.net · manuals.plus · manuals.plus · dhb3yazwboecu.cloudfront.net · manuals.plus · manualzilla.com · safe-manuals.com · pimmedia.winsupplyinc.com