E04 on a Warmflow heat pump: Electric Overheat Protection
Short answer
On a Warmflow heat pump, E04 means: Electric Overheat Protection. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 3 sources
What it means
On the Zeno R290 air source heat pump AS01-R290/AS02-R290/AS03-R290
The manual says: Electric Overheat Protection.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- The electric heater protection switch is open.
On the Zeno A-Series air source heat pump (R32) AS01-R32/AS02-R32/AS03-R32
The manual says: Electric Overheat Protection.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- The compressor is overloaded (as printed).
On the Zeno A-Series air source heat pump (R410A) AS01/AS02/AS03
The manual says: Electric Overheat Protection.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- The compressor is overloaded (as printed).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Note the exact code shown on the controller (a photo helps) and report it to your installer or the manufacturer's service line.
- Check the heat pump's supply breaker/isolator at the consumer unit is on (do not open any casing).
What the engineer will check
On the Zeno R290 air source heat pump AS01-R290/AS02-R290/AS03-R290
- Check the status of the link wire or operation of the electric heater if overheat protection is configured.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
On the Zeno A-Series air source heat pump (R32) AS01-R32/AS02-R32/AS03-R32
- Check the operation of the refrigeration circuit in terms of gas pressure and charge.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
On the Zeno A-Series air source heat pump (R410A) AS01/AS02/AS03
- Check the operation of the refrigeration circuit in terms of gas pressure and charge.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
What you might notice
Sources
- Warmflow High Efficiency Variable Speed Air Source Heat Pumps A-Series AS01-R290 / AS02-R290 / AS03-R290 - User, Installation & Service Instructions, Guarantee (9009049 Rev D) ↗ · 9009049 Rev D · page 57 · Reviewed 23 September 2026
- Warmflow High Efficiency Variable Speed Air Source Heat Pumps A-Series AS01-R32 / AS02-R32 / AS03-R32 - User, Installation & Service Instructions (9007723 Issue C) ↗ · 9007723 Issue C · page 56 · Reviewed 23 September 2026
- Warmflow High Efficiency Variable Speed Air Source Heat Pumps A-Series AS01 / AS02 / AS03 (R410A Zeno) - User, Installation & Service Instructions (Issue 7) ↗ · Issue 7 · page 49 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026