Heat pumps · Error codes · ESP
E04ESP · Ecocent heat pump water heaters (exhaust/ambient air, 80-300 l)
E04 on an ESP Ecocent heat pump water heaters: Electric Heater overheat protection: Water flow volume insufficient or the water pressure is too low
Short answer
On an ESP heat pump, E04 means: Electric Heater overheat protection: Water flow volume insufficient or the water pressure is too low. 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: Electric Heater overheat protection: Water flow volume insufficient or the water pressure is too low.
Likely causes:
- Water flow volume insufficient or the water pressure is too low.
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.
- Check the cold water supply to the cylinder is turned on.
What the engineer will check
- Check water supply is running freely and of sufficient volume.
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 34 (PDF 38) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026