HVACopediaAll brands · Heat pump troubleshooting
No mode change / wrong mode
What is going on
Possible causes and checks for: no mode change / wrong mode.
Likely causes
- Reversing valve solenoid burnt (unit stuck in de-energized mode — usually heat)
- Pilot-valve capillaries plugged
- Insufficient pressure differential, O vs B wiring. Valve that won't shift → replace
More heat pump guides
- 2 flashes: HPS open ≥6 s; 3: discharge >263°F; 4: discharge <90°F after 1 h; 5: defrost failure; 6: discharge sensor short; 7: outdoor sensor open/short; 9: bonnet sensor fail
- Excess ice on outdoor coil
- Extremely high head pressure in heating (dual fuel)
- Insufficient heat in cold weather
- Liquid slugging / compressor damage in heating
- Odour at registers (dirty sock)
Take it to the job
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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.