F07 on a Warmflow heat pump: AC Input Underload

What it means

The manual says: AC Input Underload.

Part involved: compressor driver / inverter board.

Likely causes:

• The AC input voltage is low causing the input current to be low.

Is it safe?

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

• Check the input voltage measurement.

Who to ask for: heat pump electrical / inverter.

Certification: Electrical competence; manufacturer-trained heat pump engineer.

What you might notice

• Heat pump will not start
• Keeps stopping / cutting out

What owners and engineers report

1 owner and engineer report mentions this.

• Keeps stopping / cutting out on the Zeno A-Series air source heat pump (R32) AS01-R32/AS02-R32/AS03-R32: 1 report

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 59 · 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 58 · 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 50 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026