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F34

Ferroli F34 on a gas boiler: supply voltage below 170 V

Verified with sources1 sourceReviewed Oct 3, 2026
Technician coming? See the 2 steps they must show you
Wall-mounted combi gas boiler installed in a home
Kai KemmannCC BY-SA 4.0Image source

Risk level

Low

Usually safe to check without specialist tools.

Urgency

Medium

Quick answer

Ferroli F34 means the voltage reaching the boiler is below 170 V. Check whether other lights or appliances at home dim or fail; if F34 keeps coming back, an electrician should measure the voltage and check the electrical installation.

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 valve if it is within reach, leave and call your distributor's emergency number from outside. Ferroli says to disconnect the boiler when it fails and have it repaired only by an authorised technician.
  • Do not open the consumer unit or the boiler to measure voltage. If you smell burning at sockets or the consumer unit, switch off at the main switch and call an electrician.

Safe checks you can perform

  • Lights and appliances at home
  • Whether F34 clears by itself
  • Voltage measurement by an electrician

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Boiler circuit and connection check
  • Do not attempt this professional task: Supply voltage measurement

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. Boiler circuit and connection check

    What they doThe electrician or technician checks the boiler's circuit, plug or connection and its protection devices.

    They must show youthe connection checked.

    In writingwhat was repaired or that the installation is sound.

  2. Supply voltage measurement

    What they doThe electrician measures with a multimeter the voltage reaching the boiler, at rest and with the boiler running.

    They must show youthe measured voltage against that threshold.

    In writingthe values measured and where.

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. Lights and appliances at home

    No special tools

    Who:
    you.
    How:
    when F34 appears, notice whether lights dim or flicker and whether other appliances fail.
    Result that matters:
    whether the drop affects the whole home or just the boiler.
    If other appliances fail:
    it points to the supply; contact your electricity distributor or an electrician.
    If only the boiler fails:
    it points to its circuit or connection; call an electrician.
    Evidence to keep:
    a note of the time and which appliances failed.

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

  2. Whether F34 clears by itself

    No special tools

    Who:
    you.
    How:
    F faults clear automatically when the value returns to normal, according to Ferroli. Watch the display.
    Result that matters:
    whether F34 disappears once the voltage is back.
    If it clears:
    the boiler is not necessarily faulty; note when it happens.
    If it stays:
    the voltage needs measuring.
    Evidence to keep:
    photos of the display with the times.

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

  3. Voltage measurement by an electrician

    Tools required

    Who:
    electrician or authorised technician.
    How:
    measures the voltage at the boiler's supply point and checks the circuit and consumer unit.
    Result that matters:
    whether the voltage drops below 170 V and where the drop occurs.
    If the voltage is low across the home:
    the problem is in the supply or service cable.
    If it is low only on the boiler circuit:
    that circuit or connection is repaired.
    Evidence to keep:
    a report with the measured voltage.

    Measuring mains voltage and opening the consumer unit is an electrician's job; do not do it yourself.

    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

  • Bluehelix F34
  • Error F34 Ferroli
  • F 34
  • Ferroli F 34
  • lavadora Miele bloqueo de la puerta
  • Miele F34 door will not lock
  • Miele F34 la puerta no se bloquea
  • Miele lavadora F34
  • Miele washer F34
  • Miele washing machine door lock fault

What it means

In the BlueHelix Tech RRT table, F34 is supply voltage below 170 V. Ferroli gives problems in the electricity supply as the cause and says to check the electrical installation. It is an F fault, a temporary lockout that clears by itself once the voltage is back in range. The code measures the voltage the board receives; it does not say whether the drop comes from the grid, the home's wiring or the boiler's connection.

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 valve if it is within reach, leave and call your distributor's emergency number from outside. Ferroli says to disconnect the boiler when it fails and have it repaired only by an authorised technician.

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

  • Mediumeditorial warning

    Do not open the consumer unit or the boiler to measure voltage. If you smell burning at sockets or the consumer unit, switch off at the main switch and call an electrician.

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

Symptoms and causes

Probable causes · in order

  • Voltage drop in the supplyCommon

    Ferroli lists problems in the electricity supply. It fits if lights flicker or other appliances in the home or building fail at the same time.

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

  • Problem in the home wiring or the boiler connectionPossible

    If the rest of the home is fine and only the boiler shows F34, the drop may be in its circuit, plug or connection; an electrician's measurement separates it.

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

Virtual technician

Does F34 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 2026-10-03 · verified

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