Ferroli F43 Fault Code (i25 / i29)

Safety disclaimer

Fault code summary

Manufacturer

Ferroli

Fault code

F43

Fault type

Heat exchanger, Circulation

Severity

temporary

Reset

Ferroli states that F faults reset automatically when the value returns to the normal range.

Applicable models

Ferroli i25, Ferroli i29

Quick answer

Heat-exchanger protection intervention.

What does this fault code mean?

Heat-exchanger protection intervention.

Common causes

• No system water circulation.
• Air in the system.

Symptoms

• The display flashes F43 and the boiler temporarily shuts down.

What can the homeowner safely check?

• Read the system pressure and contact the installer if the code persists.

Boiler reset information

Ferroli states that F faults reset automatically when the value returns to the normal range.

When should I call an engineer?

Contact a suitably qualified heating engineer when the fault persists, the boiler locks out, or the manufacturer instructions do not resolve it. For gas appliance work in the UK, use a Gas Safe registered engineer.

Engineer diagnosis

• Investigate pump/circulation, air and heat-exchanger protection sensing.

Applicable boiler models

• Ferroli i25
• Ferroli i29

Related fault codes

• A01 — i25 / i29

  No burner ignition.

  Read fault code
• A02 — i25 / i29

  Flame-present signal with the burner off.

  Read fault code
• A03 — i25 / i29

  Overtemperature protection intervention.

  Read fault code
• A06 — i25 / i29

  No flame after the ignition phase.

  Read fault code
• A09 — i25 / i29

  Gas-valve fault.

  Read fault code
• A15 — i25 / i29

  Air-pressure-switch fault F05 generated five times in the last 24 hours.

  Read fault code
• A16 — i25 / i29

  Gas-valve fault.

  Read fault code
• A23 — i25 / i29

  Card parameter fault.

  Read fault code

Manufacturer documentation

Table 9: F43 — Exchanger protection intervention; causes no system H2O circulation or air in system.

Last verified

2026-09-12

Frequently asked questions