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ERR

Honeywell · T10 Pro Smart Thermostat with RedLINK Room Sensor

Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor ERR Error Fix: "Err" Displayed on Screen

The thermostat is showing "Err" on the display indicating an internal hardware fault or sensor failure — this rare error typically means the built-in temperature sensor has failed or the internal circuitry is damaged; try removing the thermostat from the wall plate, waiting 30 seconds, and reattaching; if "Err" persists, the thermostat needs replacement

Medium severity2 fixes available✨ Free fix available

Quick Answer

Error ERR on the Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor means: "Err" Displayed on Screen. The top-ranked community fix is “Replace Thermostat Temperature Sensor or Thermostat Unit” (hard difficulty, ~45 min, DIY cost: $10-$20). 2 community-ranked fixes available below.

Published February 2026 · 2 fixes · thermostat

Content is based on manufacturer service documentation, community repair experience, and OEM technical bulletins. Always verify with your owner's manual.Learn about our editorial standards.

When to Call a Professional

While many thermostat repairs can be done safely at home, consider hiring a qualified technician if:

The repair involves electrical wiring, gas lines, or refrigerant
You've tried the top-ranked fix and the error persists
You smell gas, see sparking, or notice water leaking
The repair requires specialized tools you don't have
Your appliance is still under manufacturer warranty

Average professional repair cost for this issue: $120-$200.

Other Honeywell Models with Error ERR

RTH7600D 7-Day Programmable Thermostat with Backlit Display

thermostat · 2 fixes

RTH9585WF Wi-Fi Color Touchscreen 7-Day Programmable Thermostat

thermostat · 2 fixes

T6 Pro Programmable Thermostat (TH6320WF / TH6220U)

thermostat · 2 fixes

T9 Smart Thermostat with Smart Room Sensor

thermostat · 2 fixes

TH4210U2002 PRO 4000 5-2 Day Programmable Thermostat

thermostat · 2 fixes

TH6220D1028 FocusPRO 6000 2H/2C Programmable Thermostat

thermostat · 2 fixes

TH8321WF1001 VisionPRO 8000 Wi-Fi Programmable Touchscreen Thermostat

thermostat · 2 fixes

Other Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor Error Codes

APP-OFFLINE

Thermostat Shows Offline in App

"Aux Heat" Displayed

Blank/Dead Display — No Power

2 fixes

BLOWN-FUSE

HVAC Control Board Fuse Blown

2 fixes

COOL-ON-FLASH

"Cool On" Flashing on Display

2 fixes

EM-HEAT

"Em Heat" or Emergency Heat Mode

2 fixes

FAN-WONT-STOP

Fan Running Constantly

2 fixes

FILTER-REMIND

"Filter" Reminder Displayed

2 fixes

People Also Ask About Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor Error ERR

What does error code ERR mean on a Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor?

Error code ERR on the Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor means: "Err" Displayed on Screen. The thermostat is showing "Err" on the display indicating an internal hardware fault or sensor failure — this rare error typically means the built-in temperature sensor has failed or the internal circuitry is damaged; try removing the thermostat from the wall plate, waiting 30 seconds, and reattaching; if "Err" persists, the thermostat needs replacement

How do I fix error code ERR on my Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor?

The most successful fix is "Replace Thermostat Temperature Sensor or Thermostat Unit" (hard difficulty, ~45 minutes). Estimated DIY cost: $10-$20. HomeMD has 2 community-ranked fixes for this error.

Is error code ERR on a Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor serious?

This error is rated medium severity. It should be addressed soon, but your appliance may still function in a limited capacity.

Can I fix Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor error ERR myself?

Yes — the top-ranked community fix ("Replace Thermostat Temperature Sensor or Thermostat Unit") is rated hard difficulty and takes about 45 minutes. Tools needed: Flathead screwdriver, Multimeter.

How much does it cost to repair Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor error ERR?

DIY cost: $10-$20. Professional repair typically costs $120-$200. Many homeowners save money by trying the top-ranked community fix first.

What other error codes does the Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor have?

The Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor has 8 other known error codes, including: APP-OFFLINE (Thermostat Shows Offline in App), AUX-HEAT ("Aux Heat" Displayed), BLANK-SCREEN (Blank/Dead Display — No Power), BLOWN-FUSE (HVAC Control Board Fuse Blown), COOL-ON-FLASH ("Cool On" Flashing on Display), and 3 more.

Which other Honeywell models have the ERR error?

Error code ERR also appears on 7 other Honeywell models: RTH7600D 7-Day Programmable Thermostat with Backlit Display, RTH9585WF Wi-Fi Color Touchscreen 7-Day Programmable Thermostat, T6 Pro Programmable Thermostat (TH6320WF / TH6220U), T9 Smart Thermostat with Smart Room Sensor, TH4210U2002 PRO 4000 5-2 Day Programmable Thermostat, TH6220D1028 FocusPRO 6000 2H/2C Programmable Thermostat, and 1 more. The fix may vary by model, so check each model's specific page for tailored repair steps.

What other error codes does the Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor have?

The Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor has 8 other known error codes:

APP-OFFLINE — Thermostat Shows Offline in App (2 fixes)
AUX-HEAT — "Aux Heat" Displayed (2 fixes)
BLANK-SCREEN — Blank/Dead Display — No Power (2 fixes)
BLOWN-FUSE — HVAC Control Board Fuse Blown (2 fixes)
COOL-ON-FLASH — "Cool On" Flashing on Display (2 fixes)
EM-HEAT — "Em Heat" or Emergency Heat Mode (2 fixes)
FAN-WONT-STOP — Fan Running Constantly (2 fixes)
FILTER-REMIND — "Filter" Reminder Displayed (2 fixes)

Which other Honeywell models have the ERR error?

Error code ERR also appears on 7 other Honeywell models:

RTH7600D 7-Day Programmable Thermostat with Backlit Display (thermostat) · 2 fixes
RTH9585WF Wi-Fi Color Touchscreen 7-Day Programmable Thermostat (thermostat) · 2 fixes
T6 Pro Programmable Thermostat (TH6320WF / TH6220U) (thermostat) · 2 fixes
T9 Smart Thermostat with Smart Room Sensor (thermostat) · 2 fixes
TH4210U2002 PRO 4000 5-2 Day Programmable Thermostat (thermostat) · 2 fixes
TH6220D1028 FocusPRO 6000 2H/2C Programmable Thermostat (thermostat) · 2 fixes
TH8321WF1001 VisionPRO 8000 Wi-Fi Programmable Touchscreen Thermostat (thermostat) · 2 fixes

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