Ferroli · Bluehelix Tech RRT

F09 / A09Return-side over-temperature protection activated

This code applies to Bluehelix Tech RRT 24C, Bluehelix Tech RRT 28C, Bluehelix Tech RRT 34C, Bluehelix Tech RRT 18S, Bluehelix Tech RRT 24S, Bluehelix Tech RRT 30S. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.

What you can safely check

Check the system pressure and make sure accessible radiator valves are open.
Allow an overheated boiler to cool and reset once only if the user manual permits it.
If the fault returns, stop resetting and arrange an engineer.

How an engineer may fix it

Diagnose water circulation, air locks, pump operation, valves, bypass, blockages, heat exchanger and temperature sensors; restore correct flow and test the safety controls.

Code availability varies slightly between combi and system outputs; confirm the exact model manual.

Manufacturer source: Ferroli — Bluehelix Tech RRT 24C Instructions for Use, Installation and Maintenance. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.