H91 on a Panasonic heat pump: Tank heater OLP abnormality
Short answer
On a Panasonic heat pump, H91 means: Tank heater OLP abnormality. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Tank heater OLP abnormality.
Part involved: Tank (booster/immersion) heater overload protector (OLP).
When it shows: During operation of tank booster heater, and tank booster heater OLP open circuit. Service-manual table judgement: Continue for 60 sec. (L, K, J MDC, J MXC, J AIO, H, F, E, D5, D8, C).
Likely causes:
- 1 Faulty connector connection. 2 Faulty tank booster heater overload protector (OLP). 3 Faulty indoor unit PCB (main).
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
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
- Isolate power; check tank heater supply, connectors and OLP; identify overheating cause before resetting cylinder/heater thermal cut-out; check indoor PCB.
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); 215 (self-diagnosis) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026