E005 on a Rinnai heat pump: Antifreeze alarm
Short answer
On a Rinnai heat pump, E005 means: Antifreeze alarm. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 24 September 2026 · 2 sources
What it means
The manual says: Antifreeze alarm.
Part involved: water circuit frost protection.
When it shows: Outlet water below A08 (3 C); clears above +6 C; bypassed 120 s after heating start.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: unknown.
Manual reset: automatic.
What you can check
- Note the code shown on the controller and the model number on the unit's rating label before contacting your installer.
- Check that the heat pump's isolator and consumer-unit breaker are on; do not open any casing.
- Check the outdoor unit is not blocked by snow, ice, leaves or debris, and do not clear ice from the fins with tools.
What the engineer will check
- Check water flow and outlet water temperature sensor.
- Check antifreeze heaters and defrost operation.
- Check system water volume.
Who to ask for: Heat pump engineer.
Certification: Heat pump installer competence; F-gas and flammable-refrigerant (R32/R290) handling competence for any refrigerant-circuit work.
What you might notice
Sources
- Maxa i-32V5 Heat pump air/water inverters with axial fans - Controller Manual ↗ · page p.35 (MAXA i-32V5 controller manual) · Reviewed 24 September 2026
- Maxa i-290 Inverter air/water heat pumps with axial fans - Controller Manual (0106-0118) ↗ · page p.44 (MAXA i-290 controller manual) · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026