Heat pumps · Error codes · Trianco
F257Trianco · Activair Commercial R290 50kW (FG9550)
F257 on a Trianco Activair Commercial R290 50kW: Syst2: The Inverter Board Bus Over Voltage Prot
Short answer
On a Trianco heat pump, F257 means: Syst2: The Inverter Board Bus Over Voltage Prot. 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: Syst2: The Inverter Board Bus Over Voltage Prot.
Part involved: compressor driver / inverter board.
Likely causes:
- Voltage is too high.
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 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
- Check if the input voltage is higher than 480V.
Who to ask for: heat pump electrical / inverter.
Certification: Electrical competence; manufacturer-trained heat pump engineer.
What you might notice
Sources
- Trianco Activair Commercial High Temperature Air Source Heat Pump (R290 50kW FG9550) - Installation Operation and Service Manual ↗ · 2024-10 · page 41 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026