H90 on a Panasonic heat pump: Indoor/outdoor abnormal communication
Short answer
On a Panasonic heat pump, H90 means: Indoor/outdoor abnormal communication. 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 abnormal communication.
Part involved: Indoor-outdoor connection cable; indoor/outdoor PCB.
When it shows: During operation of cooling and heating, the data received from outdoor unit in indoor unit signal transmission is checked whether it is normal. Service-manual table judgement: > 1 min after starting operation (L, K, J MDC, J MXC, J AIO, H, F, E, D5, D8, C).
Likely causes:
- 1 Faulty outdoor unit PCB (main). 2 Faulty indoor unit PCB (main). 3 Indoor-outdoor signal transmiss ion error due to wrong wiring. 4 Indoor-outdoor signal transmission error due to breaking of w ire in the connection wires between the indoor and outdoor units. 5 Indoor-outdoor signal transmiss ion error due to disturbed power supply waveform.
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). Check the heat pump circuit breaker(s)/isolator at the consumer unit are ON (a tripped breaker is listed in the operating instructions' checks); if a breaker keeps tripping, leave it off and call an engineer.
What the engineer will check
- Check outdoor unit supply and isolator; check indoor/outdoor interconnecting cable for wrong wiring or breaks; check supply waveform; check indoor and outdoor PCBs.
Who to ask for: Heat pump engineer with electrical competence.
Certification: Electrical work to BS 7671 by a competent person; F-gas certification if the refrigerant circuit is opened.
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); 214 (self-diagnosis) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026