Heat pumps · Error codes · Riello
P5Riello · NXHM (R32 monobloc)
P5 on a Riello NXHM: Inlet water temp. sensor (Tw_in) malfunction [as printed; corrective actions relate to water flow / temperature difference]
Short answer
On a Riello heat pump, P5 means: Inlet water temp. sensor (Tw_in) malfunction [as printed; corrective actions relate to water flow / temperature difference]. 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: Inlet water temp. sensor (Tw_in) malfunction [as printed; corrective actions relate to water flow / temperature difference].
Likely causes:
- Valves not fully open.
- dirty filter.
- air in system.
- water pressure below 1 bar.
- pump speed.
- expansion vessel.
- circuit resistance too high.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| 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.
- Read the system pressure gauge and report the reading to your engineer (manuals ask for more than 1 bar when cold).
- Check the filling loop valves are closed.
- Restart once via the controller (OFF then ON) as the manual allows; if the code returns, call an engineer.
What the engineer will check
- Valves not fully open.
- dirty filter.
- air in system.
- water pressure below 1 bar.
- pump speed.
- expansion vessel.
- circuit resistance too high.
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