Heat pumps · Error codes · Riello
PbRiello · NXHM (R32 monobloc)
Pb on a Riello NXHM: Anti-freeze mode
Short answer
On a Riello heat pump, Pb means: Anti-freeze mode. The manual does not say whether the heat pump stops.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Anti-freeze mode.
Likely causes:
- Unit returns to normal operation automatically.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The manual does not say whether the heat pump stops.
What you can check
- Read the display; this is a protection/indication state and the manual says the unit returns to normal automatically.
- Keep the heat pump powered in cold weather so frost protection can run.
What the engineer will check
- Unit returns to normal operation automatically.
Sources
- Riello NXHM Installation and Owner's Manual (IT/EN), cod. 20192830 rev. 0 07/2021 ↗ · 20192830 rev. 0 · page PDF 65 (printed 137) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026