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F09

Ferroli F09 on a gas boiler: overtemperature protection

Verified with sources2 sourcesReviewed Oct 4, 2026
Technician coming? See the 3 steps they must show you
Wall-mounted combi gas boiler installed in a home
Kai KemmannCC BY-SA 4.0Image source

Risk level

Medium

Proceed carefully and stop if the check is unclear.

Urgency

Medium

Quick answer

Ferroli F09 means the overtemperature protection has tripped. With the boiler cold, read the gauge: it should show about 1 bar. If it is below 0.8 bar, top up with the filling key and close it. If F09 keeps coming back, call a technician.

Safety first

Stop and check this first

  • If you smell gas: do not switch lights or electrical appliances on or off, do not use anything that can spark and do not try to reset the boiler. Open the windows, leave the home and call your gas distributor's emergency number from outside.
  • Topping up the boiler every few days is not normal: it points to a water leak that a technician must trace. Ferroli recommends checking the cold system pressure regularly.

Safe checks you can perform

  • Gauge reading with the boiler cold
  • Top up with the filling key
  • When F09 appears
  • Inspection by the technician

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Check the flow or return sensor
  • Do not attempt this professional task: Pump and circulation
  • Do not attempt this professional task: Bleeding and functional test

What a technician must be able to justify

Technician visit

These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.

These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.

  1. Check the flow or return sensor

    What they doThe technician checks the sensor position on the pipe and measures its resistance with a multimeter against the manufacturer's table.

    They must show youthe value measured against the manufacturer's specification.

    In writingwhich sensor was checked and, if replaced, its part number and why.

  2. Pump and circulation

    What they doThe technician checks that the pump runs and that water circulates through the heating system.

    They must show youthe pump running and the flow and return temperatures during a demand.

    In writingthe pump condition and what was corrected.

  3. Bleeding and functional test

    What they doThe technician bleeds the air from the system and runs the boiler on heating until it reaches temperature.

    They must show youa full demand with no F09.

    In writingthe bleeding done and the final cold pressure.

Before accepting a part or repair

Nothing has been shown yet. Do not accept a part swap based on the code alone.

Follow these steps

Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.

  1. Gauge reading with the boiler cold

    No special tools

    Who:
    you.
    How:
    with the heating cold, read the boiler pressure gauge. Ferroli gives about 1 bar cold and says to restore it if it falls below 0.8 bar.
    Result that matters:
    the actual system pressure.
    If it is below 0.8 bar:
    move on to topping up.
    If it is correct:
    low pressure is ruled out; carry on with the other checks.
    Evidence to keep:
    photo of the gauge with the date.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  2. Top up with the filling key

    No special tools

    Who:
    you.
    How:
    pull out the filling key under the boiler and turn it anticlockwise while watching the gauge until it reads about 1 bar. Always close it afterwards, as Ferroli says.
    Result that matters:
    the pressure settles at its value.
    If Fh appears:
    the boiler is venting air for 300 seconds; let it finish.
    If the pressure drops again within days:
    there is a water leak that a technician must trace.
    Evidence to keep:
    photo of the final pressure.

    Do not open the casing. The drain valve is inside the boiler and is not the filling key.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  3. When F09 appears

    No special tools

    Who:
    you.
    How:
    note whether F09 shows during heating or when you run hot water, and whether it clears by itself, since F faults clear once the value is back in range.
    Result that matters:
    whether it is a one-off or keeps returning.
    If it clears and does not return:
    note the date and keep an eye on the pressure.
    If it keeps returning or stays:
    call an authorised technician, as Ferroli asks for any fault.
    Evidence to keep:
    photos of the display with the time.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  4. Inspection by the technician

    Tools required

    Who:
    an authorised heating and gas technician.
    How:
    checks the circulation pump, bleeds the air from the system and checks the position and operation of the sensor named in the table.
    Result that matters:
    which cause in Ferroli's table the measurements confirm.
    If the sensor reads out of specification:
    it is replaced and the boiler is tested.
    If the sensor is fine:
    the pump and circulation are checked before any part is changed.
    Evidence to keep:
    job sheet with the measurements and parts replaced.

    Ferroli says only authorised staff should repair the boiler and that power must be cut and the gas cock closed before working inside it.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

Still not solved

If the error persists, stop here. See what the technician must do and show you.

Where this code applies

A code is meaningful only inside the right product and version context.

Primary scope

System
Boilers
Brand
Ferroli
Product type
Gas boiler

Known code variants

  • BlueHelix F09
  • Cointra F 09
  • Error F09 Cointra
  • Error F09 Ferroli
  • F 09
  • F9
  • Ferroli F 09
  • Superlative Supra F09

What it means

In the fault tables of the BlueHelix Tech RRT 28 C and BlueHelix HiTech RRT C, F09 is the overtemperature protection tripping. Ferroli gives three causes: a faulty sensor (the return sensor on the RRT 28 C, the flow sensor on the HiTech), no water circulating in the system, or air in the system. F faults are temporary lockouts that clear by themselves once the value is back in range. The code does not say whether the water really overheated or the sensor reads wrong.

Warnings and stop conditions

  • Criticaleditorial warning

    If you smell gas: do not switch lights or electrical appliances on or off, do not use anything that can spark and do not try to reset the boiler. Open the windows, leave the home and call your gas distributor's emergency number from outside.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  • Mediumeditorial warning

    Topping up the boiler every few days is not normal: it points to a water leak that a technician must trace. Ferroli recommends checking the cold system pressure regularly.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

Symptoms and causes

Probable causes · in order

  • Faulty temperature sensorPossible

    Ferroli points to the return sensor on the RRT 28 C and the flow sensor on the HiTech. It fits if the pressure is right and F09 returns with no other visible reason.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  • No water circulating in the systemPossible

    Ferroli says to check the circulation pump and, on the HiTech, the heating system too. Only a technician can check the pump.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

  • Air in the systemPossible

    Ferroli says to bleed the air from the system. After pressure is restored, the boiler runs a venting cycle shown on the display as Fh.

    Evidence: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

Virtual technician

Does F09 still appear after these checks?

Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.

Start diagnosis

Sources and technical references

  1. 1

    Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento

    Ferroli · 2021 · manual

  2. 2

    Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimiento

    Ferroli · 2018 · manual

Sources: Ferroli BlueHelix HiTech RRT C instrucciones de uso instalación y mantenimiento · Ferroli BLUEHELIX TECH RRT 28 C instrucciones de uso instalación y mantenimientoreviewed 2026-10-04 · verified

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