H12 on a Panasonic heat pump: Indoor/Outdoor capacity unmatched
Short answer
On a Panasonic heat pump, H12 means: Indoor/Outdoor capacity unmatched. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Indoor/Outdoor capacity unmatched.
Part involved: Indoor/outdoor PCB capacity rank setting; indoor-outdoor combination.
When it shows: During startup operation of cooling and heating, the capability rank of indoor checked by the outdoor is used to determine connection capability rank abnormality. Service-manual table judgement: 90s after power supply (L, K, J MDC, J MXC, J AIO, H, F, E, D5, D8, C).
Likely causes:
- 1 Wrong model interconnected. 2 Wrong indoor unit or outdo or unit PCB (main) used. 3 Faulty indoor unit or outdoor unit PCB (main).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Not stated in the Panasonic documents opened; protection counters lock out after the stated number of occurrences.
Manual reset: User: 'Error Reset' in the remote-controller Quick Menu (H/J/K/L controllers) or OFF/ON; engineer must clear the underlying cause (service manuals: 'When error happens, the power has to be reset').
What you can check
- Read and note the code shown blinking on the remote controller (also stored under System Check > Error history). Per the Panasonic operating instructions the user may switch the system OFF/ON at the remote controller and use 'Error Reset' in the Quick Menu; if the code returns, leave the system and contact the installer (UK user guide lists Panasonic technical support as the fallback).
What the engineer will check
- Check indoor/outdoor combination against the catalogue combination table; check capacity rank set at the control panel after any indoor PCB replacement; check spare PCB part numbers match the model; check indoor/outdoor connection wiring.
Who to ask for: Heat pump installer / commissioning engineer.
Certification: None statutory.
What you might notice
Sources
- Service Manual Hydromodule WH-SDC0509L3E5/L6E5 with WH-WDG05LE5/07LE5/09LE5 (Order No PAPAMY2307068CE) ↗ · PAPAMY2307068CE · page 189 (error codes table); 191 (self-diagnosis) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026