Honeywell Thermostat Service Codes (164, 168, 170, 173): Meaning & Fixes

Honeywell T-series service alerts are the codes in the 160s and 170s — 164, 168, 170, 173, 177 and 178 — and they share one trait that separates them from everything else the thermostat displays: Resideo's definition for every one of them ends with 'contact dealer' or 'contact a professional'. This guide walks each code with its exact Resideo meaning, what the thermostat is actually reporting, and the few owner checks that are worth doing before the call — so the call you make is the right one.

How to read a T-series service alert

An active alert puts the alert icon on the home screen; on touchscreen models, touch Menu > ALERTS to read it, and on the button-style T6 Pro press Menu, step with + or − to ALRT, and press Select. Each alert shows its 3-digit number and its definition, and if several alerts are active you page through them with the arrow keys — read all of them before acting, because codes arrive in families (a 175 power notice beside a 173 fault tells a different story from a 173 alone). Write the number down exactly, with the model name from the thermostat's DEVICE INFO screen. One behavioural rule from Resideo's guides matters here: non-critical alerts can be snoozed or dismissed, but some alerts cannot be snoozed or cleared — and an alert that refuses dismissal is not being stubborn, it is classified as a fault whose cause is still present. Every code on this page is in that class: they clear when the underlying fault is repaired, not when they are acknowledged. That is also why power-cycling the thermostat is not a fix for anything below — a standing sensor or memory fault simply re-reports itself at the next self-test.

164 — Heat pump needs service

Resideo's definition is short: 'Heat pump needs service. Contact dealer to diagnose and service heat pump.' Note what the code does and does not say. It does not name a failed part, a refrigerant problem or a compressor fault — the thermostat is reporting that the heat pump system needs professional diagnosis, and on wired installations the signal path is physical: the T-series UWP mounting system provides an L/A terminal documented as the heat pump fault input, so on many systems 164 is the outdoor unit's own fault signal being passed through the thermostat to you. Owner checks before the call are therefore about context, not repair: is the outdoor unit running at all, is it icing, is the breaker on, and did the alert arrive with a loss of heating or cooling or on a system still performing? A 164 on a system that has stopped heating is an urgent call in winter; a 164 on a system still holding temperature is still a prompt call — heat pumps that report faults and keep running are usually degrading, and the dealer's diagnostic will start from this code. Do not dismiss-and-monitor 164 the way you might a filter reminder; there is no timer to reset, and the code's whole purpose is to start a service visit. One scoping note: 164 belongs to heat pump systems. A conventional furnace-and-AC installation has no heat pump to service and no fault input driving this alert, so a 164 on such a system points back at configuration — the thermostat may be set up as a heat pump controller it is not — which is again installer information, best reported exactly that way ('164 on a conventional system, no heat pump fitted') rather than silently cleared.

168 — Wi-Fi radio error (Wi-Fi models)

Resideo's Lyric T6 Pro Wi-Fi table defines 168 exactly: the Wi-Fi radio of the thermostat does not work, and wireless features are not available — and its recommended action is to contact Lyric (Resideo) technical support. The critical distinction is between 168 and the connection codes (399, 400, 508, covered in the Wi-Fi guide on this site): those describe a healthy radio failing to reach a network, a router or the internet. Code 168 describes the radio itself failing. Router reboots, password re-entry and network changes — the correct medicine for 399/400 — do nothing for a radio that has reported its own hardware error. Before calling, one observation is worth making: confirm the thermostat otherwise works (it should still control heating and cooling locally, because Wi-Fi is not in the control path), and check whether the alert followed a power surge or outage, which is useful information for support. Then make the call Resideo prescribes. On the T6 Pro Z-Wave model this code does not exist — its radio reports are 546 (Z-Wave not configured) and 547 (Z-Wave radio error), with the same 'contact dealer to replace the thermostat' endpoint.

170 — Internal memory error

Resideo's definition, identical in the Wi-Fi and Z-Wave tables: 'The memory of the thermostat has encountered an error. Please contact dealer for assistance.' The thermostat's settings, schedule and configuration live in that memory — the T6 Pro guide notes settings are permanently stored and do not require battery power — so a memory error is a fault in the one part of the thermostat everything else depends on. There is no owner procedure for 170: no reset in Resideo's documentation clears a memory error, and experimenting with factory resets on a thermostat whose memory is already faulting risks losing the configuration that a dealer will want to read or transfer. Note what still works (does it hold a setpoint, run the schedule, show the correct time?) and whether 170 arrived alone or with a 175 power-resumed notice after an outage — a single post-surge 170 that the dealer sees in context is a better diagnosis than a code reported cold. Then follow the manual: dealer assistance, with thermostat replacement the likely outcome, since the memory is not a field-replaceable part.

173 — Thermostat temperature sensor error

Resideo's definition: 'The sensor of the thermostat has encountered an error. Please contact dealer to replace the thermostat.' This is the thermostat's own built-in temperature sensor — the one that reads the room the thermostat sits in — and its failure is fundamental in a way the sensor codes below are not: without a trustworthy room-temperature reading, the thermostat cannot control anything, because every heating and cooling decision starts from that number. Symptoms that fit a genuine 173 include a displayed indoor temperature that is frozen, implausible, or wildly at odds with the room while the system runs long or not at all. Do not confuse 173 with a calibration complaint: a thermostat that reads a degree or two off is a placement or offset question, not a sensor error, and it will not set 173. Equally, do not let anyone sell you a remote sensor as the cure — 173 is the internal sensor, and Resideo's stated fix is thermostat replacement by the dealer. While you wait for that visit, the system has no reliable automatic control; run it manually and conservatively, and protect against the extremes (frozen pipes in winter, heat stress in summer) the way you would with any dead thermostat.

177 — Indoor temperature sensor error (wired remote sensor)

Resideo's definition: 'Wired indoor temperature sensor is not connected or there is a wiring short. Please contact dealer for assistance.' The Lyric T6 guide's alert list phrases the same fault as: the remote indoor temperature sensor is not connected or the wiring is faulty (noted as a T6-only feature in that guide). Two things follow. First, 177 only exists on systems that actually have a wired remote indoor sensor on the S terminals — if your system has none and 177 appears, the thermostat's configuration believes one is fitted, which is itself diagnostic information for the installer. Second, unlike 173, this fault lives in a replaceable external part and its wire run: the sensor itself, a short in the run, or a connection lost at either end. The fix is methodical installer work — prove the wiring, test or swap the sensor — not thermostat replacement. Owner contribution: report any recent work near the sensor or its wiring (painting, picture hooks, rodent activity in a wall are all real-world causes of suddenly-open sensor runs) and whether the displayed temperature reverted to the thermostat's own sensor or vanished, both of which help the installer start in the right place.

178 — Outdoor temperature sensor error (wired outdoor sensor)

Resideo's definition mirrors 177 exactly, one wire-run further out: 'Wired outdoor temperature sensor is not connected or there is a wiring short. Please contact dealer for assistance.' The outdoor sensor (also on the S terminals) feeds the thermostat information that, depending on configuration, drives the outdoor-temperature display, heat-pump balance-point and dual-fuel changeover decisions — so a failed outdoor sensor can degrade heat-pump control strategy even though the house still heats. That is the reason to take 178 seriously on a heat pump system and treat it as routine-but-booked on a conventional system that only displays outdoor temperature. Causes sit in the same family as 177: a failed sensor, a shorted or open run of wire, or connections lost at the sensor or the thermostat — with weather, sunlight and garden tools added to the suspect list, because this sensor lives outdoors. Owner checks stop at observation: is the sensor still physically present and intact where it was mounted, and did the alert follow any outdoor work? The electrical proof (the manuals publish resistance behaviour for their NTC sensors) is installer work with a meter, and Resideo routes the code to the dealer for exactly that reason.

Sensor error or equipment error? Reading the service family as a whole

Step back and the six codes divide cleanly by where the fault lives. Codes 173, 177 and 178 are the sensor family — the thermostat's own temperature sensor, then the two wired remote sensors — and they divide again by replaceability: 177 and 178 are external parts and wiring an installer can test and swap, while 173 is internal and ends in thermostat replacement. Code 170 stands alone as the thermostat's own electronics (memory), also ending at the dealer and likely at replacement. Code 168 is the thermostat's radio — hardware again, routed to Resideo support. Only 164 points away from the thermostat entirely: it is the heat pump asking for service, with the thermostat as messenger. That division is the practical value of reading the exact number: a homeowner who reports 'a sensor error' sends the dealer in blind, while '178, outdoor sensor, on a dual-fuel system' sends them in with the right sensor in the van. It also protects you from the two classic misdiagnoses — replacing a thermostat for a broken outdoor-sensor wire (178 misread as 173), and resetting a thermostat for a heat pump fault (164 misread as a glitch). Match the number to its definition in Resideo's table, every time, before any part is bought.

54 — Thermostat humidity sensor error (the code the Wi-Fi tables skip)

One more service-family code deserves a line because owners meet it on the Z-Wave and button-style models whose tables include it: 54, thermostat humidity sensor error — in Resideo's words, 'the sensor of the thermostat has encountered an error', with the same endpoint as 173: contact the dealer to replace the thermostat. The Wi-Fi models' alert references start their tables at 164, so a T6 Pro Smart owner will not find 54 listed even though the code circulates in T-series documentation; scope is per model table, not per brand. The fault itself is the humidity counterpart of 173: an internal sensing element the thermostat uses for humidity display and for humidification/dehumidification control has failed its self-check. A wrong humidity reading alone — a few percent off a reference hygrometer — is not a 54 and sets no code; 54 means the sensor reported an error, not an inaccuracy. Because the humidity sensor is internal, the fix path is the internal-sensor path: no wiring to reseat, no external part to swap, and Resideo's stated cure is dealer replacement of the thermostat. If humidity control matters in your house (a humidifier or dehumidifier under the thermostat's control), treat 54 as more than cosmetic: the thermostat is making moisture decisions from a sensor it has itself declared faulty.

What to tell the dealer (and what not to do first)

Resideo routes every code on this page to a professional, so the owner's job is to make that visit count. Report: the exact code number and model (from DEVICE INFO), when the alert first appeared, what the system was doing at the time (heating, cooling, defrost, just after an outage), any companion alerts (175 and 171 place the event in a power story), and any recent work anywhere near the thermostat, sensors or outdoor unit. Photograph the alert screen before the visit if you can — a fault alert that happens to clear leaves little behind. What not to do: do not factory-reset the thermostat (you may erase the configuration the dealer needs, and no code on this page is documented as reset-curable); do not open the thermostat or the equipment to 'check the sensor wiring' (Resideo's installation cautions treat wiring work as power-disconnected, trained-technician work); and do not keep a failed-sensor system (173) running unattended on automatic control — a thermostat that cannot measure the room cannot be trusted to protect the house. The codes did their job by naming the fault family precisely; the fastest route back to automatic comfort is a dealer who arrives already knowing which family it is.

Key takeaways

• Quote the full code AND the model when you call — 177 and 173 differ by one digit and opposite fixes (a wire run vs a thermostat replacement).
• An alert that cannot be snoozed or dismissed is Resideo telling you it is a fault, not a reminder — believe it and book the visit.
• Photograph the alert screen: fault alerts clear when their cause clears and leave no owner-visible history.

Resetting the Honeywell thermostat

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.

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Related guides

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