Heat pumps · Error codes · ESP
4ESP · Classic / Classic II fixed-speed air/water (PASRW-0x0B-KA/KD)
4 on an ESP Classic / Classic II fixed-speed air/water: Compressor exhaust temp too high (Compressor exhaust temp too high)
Short answer
On an ESP heat pump, 4 means: Compressor exhaust temp too high (Compressor exhaust temp too high). 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: Compressor exhaust temp too high (Compressor exhaust temp too high).
Likely causes:
- Compressor exhaust temp too high.
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.
What the engineer will check
- Check through the refrigerant system for faults and overloading.
Who to ask for: heat pump engineer.
Certification: F-gas certified engineer (refrigerant circuit).
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