E04 on a Trianco heat pump: Electric Heater Overload Prot
Short answer
On a Trianco heat pump, E04 means: Electric Heater Overload Prot. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 5 sources
What it means
On the Activair Commercial R290 50kW (FG9550)
The manual says: Electric Heater Overload Prot.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- Electric heating overheat protection switch is disconnected.
On the Activair High Temperature R290 (5/9/15/22kW)
The manual says: Electric heater overheat Protection.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- Electrical heating overheat protector open.
On the Activair R290 Indoor (3.2kW wall hung / 5kW floor standing)
The manual says: Electric Heater Overheat Fault.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- The electric-heater protection switch is broken.
On the Activair R410A indoor wall hung 3kW (S300)
The manual says: Discharge overheating protection.
Part involved: pressure switch / compressor discharge-suction.
On the Activair Pro (AI) R290 6/12/17kW
The manual says: Electric Heater Overheat Fault.
Part involved: electric heater / immersion overheat protection.
Likely causes:
- The electric-heater protection switch is broken.
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
On the Activair Commercial R290 50kW (FG9550)
- 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).
On the Activair High Temperature R290 (5/9/15/22kW)
- 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).
On the Activair R290 Indoor (3.2kW wall hung / 5kW floor standing)
- 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).
On the Activair R410A indoor wall hung 3kW (S300)
- 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).
- Check the outdoor unit is not blocked by debris/snow and has its required clearances.
On the Activair Pro (AI) R290 6/12/17kW
- 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 Activair Commercial R290 50kW (FG9550)
- Inspect whether the electric heating is under operation condition of over 150C for a long time.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
On the Activair High Temperature R290 (5/9/15/22kW)
- Check if the Electrical heating Overheat protector is open or not.
- Check the Electrical heater.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
On the Activair R290 Indoor (3.2kW wall hung / 5kW floor standing)
- Check whether the electric heater runs at the temperature above 150C for a long time.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
On the Activair R410A indoor wall hung 3kW (S300)
- Check if the refrigerant system has leak points or is blocked.
Who to ask for: refrigeration.
Certification: F-gas certified refrigeration engineer (REFCOM or equivalent).
On the Activair Pro (AI) R290 6/12/17kW
- Check whether the electric heater runs at the temperature above 150C for a long time.
Who to ask for: electrical.
Certification: Electrical competence (Part P / qualified electrician).
What you might notice
What owners and engineers report
1 owner and engineer report mentions this.
- Hot water not hot enough on the Activair High Temperature R290 (5/9/15/22kW): 1 report
Sources
- Trianco Activair Commercial High Temperature Air Source Heat Pump (R290 50kW FG9550) - Installation Operation and Service Manual ↗ · 2024-10 · page 39 · Reviewed 23 September 2026
- Trianco Activair High Temperature Air Source Heat Pump (R290 5/9/15/22kW) - Installation Operation and Service Manual ↗ · November 2024 (PDF regenerated 2026-08) · page 34 · Reviewed 23 September 2026
- Trianco Activair R290 High Temperature Indoor Air Source Heat Pump (3.2kW wall hung) - Installation Operation and Service Manual ↗ · 2026-08 · page 32 · Reviewed 23 September 2026
- Trianco Activair Wall Hung Air Source Heat Pump S300 (R410A indoor) - Installation Operation and Service Manual ↗ · 2023-07 · page 33 · Reviewed 23 September 2026
- Trianco Activair Pro Air Source Heat Pump (R290 6/12/17kW) - Installation Operation and Service Manual ↗ · 06/2026 · page 39 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026