Heat pumps · Error codes · Riello
P0Riello · NXHM (R32 monobloc)
P0 on a Riello NXHM: Low pressure switch protection
Short answer
On a Riello heat pump, P0 means: Low pressure switch protection. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Low pressure switch protection.
Likely causes:
- Refrigerant shortage.
- outdoor heat exchanger dirty/blocked (heating/DHW).
- water flow too low in cooling.
- electronic expansion valve stuck or winding loose.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Read and note the exact code shown on the controller display.
- Check the heat pump's breaker/isolator at the consumer unit is on.
- Check the outdoor unit is not blocked by leaves, debris or snow and has clear space around it.
- Restart once via the controller (OFF then ON) as the manual allows; if the code returns, call an engineer.
What the engineer will check
- Refrigerant shortage.
- outdoor heat exchanger dirty/blocked (heating/DHW).
- water flow too low in cooling.
- electronic expansion valve stuck or winding loose.
Sources
- Riello NXHM Installation and Owner's Manual (IT/EN), cod. 20192830 rev. 0 07/2021 ↗ · 20192830 rev. 0 · page PDF 67 (printed 139) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026