F25 on a Trianco heat pump: LP 15V Under load Fault
Short answer
On a Trianco heat pump, F25 means: LP 15V Under load Fault. 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 · 3 sources
What it means
On the Activair High Temperature R290 (5/9/15/22kW)
The manual says: LP 15V Under load Fault.
Part involved: compressor driver / inverter board.
Likely causes:
- 15V supply low.
On the Activair R290 Indoor (3.2kW wall hung / 5kW floor standing)
The manual says: Input Power Current Sampling Fault.
Part involved: compressor driver / inverter board.
Likely causes:
- The V15V is overload or undervoltage.
On the Activair Pro (AI) R290 6/12/17kW
The manual says: Input Power Current Sampling Fault.
Part involved: compressor driver / inverter board.
Likely causes:
- +15 V supply is overvoltage or undervoltage.
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
On the Activair High Temperature R290 (5/9/15/22kW)
- Check if the power supply is stable and restart the unit.
- If the problem persists, replace the drive board.
Who to ask for: heat pump electrical / inverter.
Certification: Electrical competence; manufacturer-trained heat pump engineer.
On the Activair R290 Indoor (3.2kW wall hung / 5kW floor standing)
- Check the V15V input voltage in range 13.5V~16.5V or not.
Who to ask for: heat pump electrical / inverter.
Certification: Electrical competence; manufacturer-trained heat pump engineer.
On the Activair Pro (AI) R290 6/12/17kW
- Verify that the +15 V supply is within 13.5-16.5 V.
Who to ask for: heat pump electrical / inverter.
Certification: Electrical competence; manufacturer-trained heat pump engineer.
What you might notice
Sources
- 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 36 · 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 34 · Reviewed 23 September 2026
- Trianco Activair Pro Air Source Heat Pump (R290 6/12/17kW) - Installation Operation and Service Manual ↗ · 06/2026 · page 42 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026