ErrorBase
Independent technical referenceOfficial site
  • Boilers
  • Gas boiler

A05

Ferroli A05 on a gas boiler: fan supply, signal or fan fault

Verified with sources1 sourceReviewed 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

High

Professional inspection is recommended.

Urgency

High

Quick answer

Ferroli A05 means a fan fault: no 230 V supply, a broken tachometer signal or a faulty fan. Make a single reset with the reset key for 1 second. If it returns, call an authorised technician.

Safety first

Stop and check this first

  • If you smell gas, do not reset: do not touch switches or light flames, open windows, close the gas tap if it is within reach, leave and call your gas distributor's emergency number from outside. Ferroli leaves repairs to authorised technicians.
  • If you smell fumes or anyone has a headache, dizziness or nausea near the boiler, switch it off, ventilate and get outside: there may be carbon monoxide, which has no smell. Call the technician and do not switch it back on until the flue has been checked. A CO alarm gives early warning.
  • Do not chain resets: Ferroli says that if the boiler does not restart, the fault must be fixed. The TECH table also lists A64, maximum number of consecutive resets exceeded.

Safe checks you can perform

  • Smell of gas or combustion fumes
  • A single reset with the reset key
  • Flue terminal seen from outside
  • Fan and connector checked by the technician

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Fan supply voltage
  • Do not attempt this professional task: 5 pin connector and tachometer signal
  • Do not attempt this professional task: Combustion analysis after replacing the fan

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. Fan supply voltage

    What they doWith the boiler open and following safety rules, the technician measures with a multimeter whether 230 V reaches the fan when the board calls for it.

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

    In writingthe measurement and the decision taken.

  2. 5 pin connector and tachometer signal

    What they doThe technician checks the wiring and the 5 pin connector of the fan, including the tachometer signal line to the board.

    They must show youthe connector checked, with a photo.

    In writingthe repair carried out.

  3. Combustion analysis after replacing the fan

    What they doIf the fan is replaced, the technician puts the boiler in test mode and measures CO2 at maximum and minimum output with an analyser.

    They must show youthe analyser printout.

    In writingthe values measured against the manufacturer's specification and the part number of the new fan.

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. Smell of gas or combustion fumes

    No special tools

    Who:
    you.
    How:
    first, check whether there is a smell of gas or combustion fumes near the boiler, or whether anyone has a headache, dizziness or nausea.
    Result that matters:
    whether it is safe to carry on with the checks for A05.
    If you smell gas:
    do not touch the boiler; follow the gas warning and call from outside.
    If you smell fumes:
    switch the boiler off, ventilate and call the technician; do not reset.
    Evidence to keep:
    a note of the time and what you noticed.

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

  2. A single reset with the reset key

    No special tools

    Who:
    you.
    How:
    Ferroli says faults with the letter A lock the boiler out and that it is reset by pressing the reset key for one second, or with the remote timer control reset if you have one. Do it once only.
    Result that matters:
    whether the boiler starts and A05 does not return.
    If it works:
    note the date and time; if A05 repeats, the technician must know there was already a reset.
    If it returns:
    do not keep trying; Ferroli says the fault must be fixed if the boiler does not restart.
    Evidence to keep:
    photo of the code before and after the reset.

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

  3. Flue terminal seen from outside

    No special tools

    Who:
    you.
    How:
    look at the air intake and flue terminal from the ground or a window, without touching it or climbing.
    Result that matters:
    whether it is damaged or has objects in it, useful for the technician.
    If you see damage or a blockage:
    tell the technician along with the code.
    If it looks fine:
    the most likely cause is the fan or its connection.
    Evidence to keep:
    photos of the terminal.

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

  4. Fan and connector checked by the technician

    Tools required

    Who:
    authorised gas technician.
    How:
    checks that 230 V reaches the fan, checks the 5 pin connector wiring and the tachometer signal and, if all arrive correctly, the fan.
    Result that matters:
    which of the three causes in the table is confirmed.
    If power or signal is missing:
    the wiring or connector is repaired.
    If power and signal are fine:
    the fan is replaced.
    Evidence to keep:
    job sheet with what was measured and the part replaced.

    Ferroli says to disconnect the power and close the gas tap before any work inside. Opening the casing is not a job for the user. The fan and its wiring are technician only.

    Evidence: 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

  • A 05
  • A5
  • BlueHelix Tech A05
  • Cointra A 05
  • Error A05 Cointra
  • Error A05 Ferroli
  • Ferroli A05
  • Superlative A05

What it means

On the BlueHelix TECH RRT 28 C, A05 is a fan fault; the fan supplies combustion air and pushes out the flue gases. Ferroli gives three causes: no 230 V supply to the fan, a broken tachometer signal, which is the speed signal the board reads, and a faulty fan. For the first two it says to check the wiring of the 5 pin connector and for the third, the fan. A faults lock out until reset. The code does not say which of the three causes it is.

Warnings and stop conditions

  • Criticaleditorial warning

    If you smell gas, do not reset: do not touch switches or light flames, open windows, close the gas tap if it is within reach, leave and call your gas distributor's emergency number from outside. Ferroli leaves repairs to authorised technicians.

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

  • Higheditorial warning

    If you smell fumes or anyone has a headache, dizziness or nausea near the boiler, switch it off, ventilate and get outside: there may be carbon monoxide, which has no smell. Call the technician and do not switch it back on until the flue has been checked. A CO alarm gives early warning.

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

  • Highsource verified

    Do not chain resets: Ferroli says that if the boiler does not restart, the fault must be fixed. The TECH table also lists A64, maximum number of consecutive resets exceeded.

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

Symptoms and causes

Probable causes · in order

  • No 230 V supply to the fanPossible

    If the fan gets no power it does not turn. Ferroli says to check the 5 pin connector wiring before touching the fan.

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

  • Tachometer signal brokenPossible

    The fan may turn but the board does not receive its speed signal. Checking the same 5 pin connector and its cable tells it apart.

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

  • Fan faultyPossible

    If power and signal arrive correctly and the fault remains, Ferroli says to check the fan, which is the part that gets replaced.

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

Virtual technician

Does A05 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 TECH RRT 28 C instrucciones de uso instalación y mantenimiento

    Ferroli · 2018 · manual

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

Was this entry useful?