Heat pumps · Error codes · ESP
1ESP · Classic / Classic II fixed-speed air/water (PASRW-0x0B-KA/KD)
1 on an ESP Classic / Classic II fixed-speed air/water: Cooling water freezing (Cooling water temp. too low)
Short answer
On an ESP heat pump, 1 means: Cooling water freezing (Cooling water temp. too low). 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: Cooling water freezing (Cooling water temp. too low).
Likely causes:
- Cooling water temp. too low.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes (table "Recover: Yes").
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.
- Check the system pressure gauge reading.
What the engineer will check
- Check water flow volume and temp setting and controller.
Who to ask for: heat pump engineer.
Sources
- ESP Classic II 13kW, 15kW, 17kW & 25kW Air Source Heat Pump - Installation & Operation Manual V2.3 (PASRW-040B-KA/050B-KA/060B-KA/080B-KA/080SB-KA) ↗ · V 2.3 · page 39-40 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026