Heat pumps · Error codes · ESP
P04ESP · Ecocent heat pump water heaters (exhaust/ambient air, 80-300 l)
P04 on an ESP Ecocent heat pump water heaters: Ambient temp sensor failure: Sensor is open or short-circuit
Short answer
On an ESP heat pump, P04 means: Ambient temp sensor failure: Sensor is open or short-circuit. 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: Ambient temp sensor failure: Sensor is open or short-circuit.
Likely causes:
- Sensor is open or short-circuit.
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
- 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 sensor and change if necessary.
Who to ask for: heat pump engineer.
Sources
- ESP Ecocent 200 & 300L Installation and Operation Manual V2.3 (ESP400-10-200L and 300L) ↗ · V 2.3 · page 33 (PDF 37) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026