H75 on a Panasonic heat pump: Low water temperature control

What it means

The manual says: Low water temperature control.

Part involved: Indoor heat exchanger protection (back-up heater disabled).

When it shows: Service-manual table judgement: Room heater disable and deice request to operate under low water temperature (L, K, J MDC, J MXC, J AIO, H).

Likely causes:

• 1 Back-up heater “Disable” under custom menu.

Is it safe?

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).

What the engineer will check

• Check back-up heater is enabled in installer settings (heater operation must be enabled to raise water temperature); check return water temperature and defrost conditions.

Who to ask for: Heat pump installer / commissioning engineer.

Certification: None statutory.

What you might notice

• Unexpected backup / auxiliary heater use
• Insufficient heating (house not warm enough)

Sources

• Service Manual Hydromodule WH-SDC0509L3E5/L6E5 with WH-WDG05LE5/07LE5/09LE5 (Order No PAPAMY2307068CE) ↗ · PAPAMY2307068CE · page 189 (error codes table) · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026