FP on a WaterFurnace Envision NSKW / TruClimate 100 hydronic 50 Hz: Freeze Detection (FP): Refrigerant loop temperature below the FP value (service menu) for 30 continuous seconds; compressor and loop pumps disabled; 2-minute bypass at start-up
Short answer
On a WaterFurnace heat pump, FP means: Freeze Detection (FP): Refrigerant loop temperature below the FP value (service menu) for 30 continuous seconds; compressor and loop pumps disabled; 2-minute bypass at start-up. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Freeze Detection (FP): Refrigerant loop temperature below the FP value (service menu) for 30 continuous seconds; compressor and loop pumps disabled; 2-minute bypass at start-up.
When it shows: retry fault (2 retries then lockout).
Likely causes:
- Refrigerant loop temperature below the FP value (service menu) for 30 continuous seconds; compressor and loop pumps disabled; 2-minute bypass at start-up.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: place unit in standby for at least 5 s or cycle control power.
What you can check
- Note the code and any text shown on the display/controller.
- Check the heat pump isolator and consumer-unit breaker are on.
What the engineer will check
- Diagnose per NSKW installation manual troubleshooting.
- Check loop antifreeze concentration and loop flow.
Who to ask for: heat pump engineer.
Sources
- NSKW Installation Manual - Geothermal Hydronic Heat Pump 50 Hz, NSKW 06 to 17 kW (IM1066WN 03/16) ↗ · IM1066WN 03/16 · page 26 (printed 27) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026