HVAC & Thermostats: error codes & repairs by brand
Thermostat faults and mini-split error codes — Nest, ecobee, Honeywell, Mitsubishi, Daikin, and LG. Know when it's a $0 fix and when to call an HVAC tech.
Google Nest
Nest Learning Thermostat and Nest Thermostat
3 guides · E/H/W codes (E73, E74…) and power messages
ecobee
ecobee smart thermostats (SmartThermostat, ecobee3/4)
2 guides · Message-based faults (calibrating, no power…)
Honeywell Home
T-series and classic Honeywell Home thermostats
3 guides · Display messages ('Cool On' blinking, 'Wait'…)
Mitsubishi Electric
Mr. Slim / M-Series mini-split systems
2 guides · E/P/U codes and blink patterns (E6…)
Daikin
Daikin mini-split and light-commercial systems
2 guides · Letter-number codes (U4, A-codes…)
LG
LG mini-split and multi-split systems
2 guides · CH codes (CH 05…)
Carrier
Carrier gas furnaces and light-commercial units (Bryant/Payne share the platform)
5 guides · LED status codes (31, 33, 34, 13…)
Trane
Trane gas furnaces and light-commercial units (American Standard shares the platform)
5 guides · Status-LED flash codes (2–5 flashes…)
Lennox
Lennox gas furnaces (SureLight and current EL/SL series)
6 guides · E-codes (E200–E271) and Watchguard
Rooftop Units (RTUs)
Packaged rooftop units, all brands, ~3–25 ton — the machine over most offices
2 guides · Common failure guides (economizers, belts, drains)
All Brands — Universal
Cross-brand furnace and AC fixes every office should know
2 guides · Symptom-based guides