Vokera Boiler Error Codes: Complete Diagnostic Guide

Summary

Vokèra has been sold in the UK domestic boiler market for several decades, with the Compact, Linea, Mynute, and Evolve ranges covering combi, system, and regular formats across multiple product generations. The great majority of the installed base — Compact, Linea, and standard Mynute models — uses a consistent two-digit "A" fault code scheme (A01–A77), confirmed against the manufacturer's own Mynute i20 fault code table and cross-checked against multiple independent UK trade sources. The Mynute i-series adds a small number of "AL"-prefixed codes for low-pressure conditions (AL40, AL41) alongside the standard A-codes. The newer Evolve range uses a visually similar but functionally different "E0"-prefixed scheme (E10, E020, E030, E040/E041, E090, and others) — critically, an Evolve E10 means flame lockout, not low pressure, so a code number cannot be assumed to carry the same meaning across ranges.

This matters on site: the single biggest diagnostic mistake with Vokèra boilers is assuming a code number carries across models without checking which range and generation is in front of you. Before quoting a fix from a code alone, identify the exact model and confirm the code family against the chart printed on the inside of the front casing or in the installation and servicing instructions for that specific unit.

This guide covers the A-code scheme that applies to the majority of the Vokèra domestic range, the diagnostic steps for each common fault, and flags explicitly where the Evolve range's E0-prefixed codes diverge from the A-code meanings.

Key Facts

• The majority of the Vokèra range (Compact, Linea, standard Mynute) displays fault codes as "A" followed by two digits (e.g. A01, A04) on the front panel
• The Mynute i-series adds "AL"-prefixed codes for low-pressure conditions (AL40, AL41) alongside the standard A-code set
• The newer Evolve range uses a separate "E0"-prefixed scheme (e.g. E10, E020, E030, E090) that does not share meanings with the A-code scheme — an Evolve E10 is a flame lockout, not a pressure fault
• The boiler locks out on most fault codes and requires a manual reset — typically a dedicated reset button on the front panel, held briefly until the display clears
• A01 (ignition failure) and A04 (insufficient system water pressure) are the two most consistently documented codes across the A-code range and the two most common callout reasons
• Repeated resetting of a persistent fault code risks damage to components (particularly A02 limit-thermostat/overheat and ignition-related faults) and should not be used as a substitute for diagnosis
• Vokèra boilers require annual servicing by a Gas Safe registered engineer under the Gas Safety (Installation and Use) Regulations 1998
• Vokèra is a brand of the Riello Group (Italian heating manufacturer, Legnago, Verona) — confirm the specific model's parts sourcing and manual with Vokèra/Riello directly rather than assuming interchange with another brand
• The Benchmark commissioning log (where completed) should be checked first on any callout — missing or incomplete records can indicate a boiler that was poorly commissioned, which is itself a common root cause of recurring nuisance lockouts

Quick Reference Table

Detailed Guidance

What does A01 mean on a Vokèra boiler?

A01 — Ignition Failure (Flame Not Sensed)

The boiler attempted ignition and failed to establish a flame within the safety window, most often after three attempted sparks. This is the most common Vokèra callout code and shares the same underlying cause hierarchy seen across the wider condensing boiler market.

Likely causes, in rough order of probability:

1. No gas supply — pre-payment meter exhausted, gas cock closed, isolation valve at the boiler shut. Check other gas appliances in the property before opening the casing.
2. Frozen condensate pipe — very common between November and March. Ice forms at an external run, elbow, or the termination point, backing pressure up into the trap and preventing the boiler from firing. Thaw with warm (not boiling) water; never use a naked flame.
3. Ignition electrode fault — worn tip, cracked porcelain, carbon build-up, or a damaged HT lead preventing a reliable spark.
4. Gas valve fault — coil failure or intermittent operation; listen for the valve click during an ignition attempt.
5. Low gas pressure — inlet pressure below 17 mbar (natural gas); check at the meter and again at the boiler inlet test point.
6. Flue restriction — bird nest, debris, or an incorrectly fitted terminal causing recirculation of combustion products.

Diagnostic steps:

1. Confirm gas supply is live and other appliances are working.
2. Check for a frozen condensate pipe in cold weather — this alone resolves a large share of winter A01 callouts.
3. Reset once and observe the ignition attempt directly if possible — listen and look for spark and gas valve operation.
4. If no spark, check electrode condition, gap, and HT lead continuity.
5. If spark is present but no ignition, check gas pressure at the boiler with a manometer at the test point.
6. Inspect the flue terminal for obstruction if the above checks are clear.

What does A04 mean on a Vokèra boiler?

A04 — Insufficient System Water Pressure

The pressure sensor has detected system pressure below the boiler's minimum operating threshold. This is the one common Vokèra fault a competent homeowner can usually resolve themselves, and the one worth talking a customer through over the phone before booking a visit. On the Mynute i-series specifically, this same fault may display as AL40 or AL41 rather than A04 — check the model.

Likely causes, in rough order of probability:

1. System leak — a weeping radiator valve, pipe joint, or dripping automatic air vent is the most common cause of a recurring A04.
2. PRV discharge — check the external discharge pipe for wetness; a discharging pressure relief valve points to an expansion vessel fault or system waterlogging.
3. Recent radiator bleed without repressurising afterwards.
4. Expansion vessel fault — lost pre-charge or a failed diaphragm, causing the PRV to lift on heat-up.
5. Pressure sensor fault — less common, but possible on an older unit reading incorrectly low.

Diagnostic steps:

1. Check the pressure gauge — if genuinely low, repressurise via the filling loop to the level stated on the boiler data plate (typically 1.0–1.5 bar cold).
2. Reset and monitor pressure through a heating cycle; a rise of roughly 0.3–0.5 bar during heat-up is normal.
3. If pressure rises excessively on heat-up, suspect the expansion vessel — check the Schrader valve for water (diaphragm failure) and pre-charge pressure against the data plate figure.
4. If pressure drops away again over hours or days, investigate for leaks systematically: radiator valves, pipe joints, boiler internals, PRV outlet.
5. If the gauge reads correctly but A04 persists, suspect the pressure sensor itself.

Do not confuse with Evolve E10. On the Evolve range, a code displayed as E10 means flame lockout, an entirely different fault requiring ignition-chain diagnosis, not repressurising. Confirm the range before acting on a code number alone.

What does A02 mean on a Vokèra boiler?

A02 — Limit Thermostat Fault (Overheat / STB Tripped)

The safety temperature limiter has activated because the boiler has exceeded its safe operating temperature. This points to a circulation problem and should not be repeatedly reset without investigation.

Likely causes:

1. Pump failure or seizure preventing water flow through the heat exchanger.
2. System or heat exchanger blockage from sludge/scale, restricting flow.
3. Air lock preventing circulation.
4. Faulty NTC thermistor giving a false high reading (less common).

Diagnostic steps: allow the boiler to cool fully before investigation; confirm the pump is running and not seized; check for flow through the system (are radiators heating?); check flow/return temperature differential under load — a large differential points to restricted flow through the heat exchanger.

Warning: repeated resetting of a genuine overheat fault risks heat exchanger damage. Diagnose the circulation issue before returning the boiler to service.

What does A09 mean on a Vokèra boiler?

A09 — Flue Thermistor or Flue Thermistor Counter Fault

The control board has detected a fault on the flue thermistor circuit, or the flue thermistor has recorded repeated over-temperature events (the "counter" fault). This is not a gas valve fault — it relates to the flue gas temperature sensing circuit and, where the counter has tripped, may indicate an underlying combustion or flue restriction problem that has caused repeated flue over-temperature events.

Likely causes: flue thermistor sensor failure or wiring fault; a genuine pattern of flue over-temperature events caused by restricted flue draught, incorrect burner setting, or heat exchanger fouling; control board fault.

Action: check the flue thermistor and its wiring first. If the counter fault is present (repeated over-temperature trips rather than a single sensor failure), investigate the underlying combustion/flue issue — check flue for obstruction and confirm combustion performance with a flue gas analyser — rather than simply replacing the sensor and resetting.

Fault categories where the exact code should be confirmed on site

For A03, A06, A07, A08, A11, and A77, and for any code shown on a model not covered in the table above, the general fault category (fan, thermistor/sensor, configuration, false flame) is consistent with the manufacturer's own Mynute i20 fault code documentation, but always open the model-specific fault chart — printed inside the front casing on most models, or in the installation and servicing instructions — before committing to a diagnosis or ordering parts based on the code number alone. This is especially important on the Evolve range, which uses a different E0-prefixed scheme where the same two digits mean a different fault to the A-code range.

Diagnostic decision tree — boiler in lockout, no ignition (A01)

Boiler displays A01, will not fire
              |
              v
   Confirm gas supply live at meter
   and at other appliances
              |
      +-------+-------+
      |               |
   No gas           Gas present
   supply               |
      |          Check condensate pipe
  Restore gas,   for ice (esp. Nov-Mar)
  reset, monitor        |
                +-------+-------+
                |               |
             Frozen          Not frozen
                |               |
          Thaw with warm    Reset once,
          water, reset,     observe
          monitor           ignition attempt
                                   |
                          +--------+--------+
                          |                 |
                     No spark          Spark present,
                          |             no flame
                Check electrode,             |
                HT lead, gap          Check gas pressure
                                       at boiler inlet
                                       (manometer, test point)

Diagnostic decision tree — low pressure fault (A04 / AL40 / AL41)

A04 (or AL40/AL41 on Mynute i-series) displayed
              |
              v
   Check pressure gauge reading
              |
      +-------+-------+
      |               |
  Genuinely low    Gauge reads normal
      |               |
  Repressurise    Suspect pressure
  via filling     sensor fault --
  loop to data    check wiring,
  plate figure    resistance
      |
  Reset, monitor pressure
  through a heating cycle
      |
  +---+---+
  |       |
Holds   Drops again
  |       |
Monitor  Systematic leak check:
         radiator valves, joints,
         PRV, boiler internals

Frequently Asked Questions

How do I reset a Vokèra boiler after a fault code?

Press and hold the reset button on the front panel for the period stated in the manual (typically a few seconds) until the display clears. If the fault code returns immediately, there is an active fault requiring diagnosis — do not keep resetting, particularly for A02 (overheat) or A11/A01 (ignition-related) type faults, where repeated resetting risks component damage or is unsafe.

Can I keep using the boiler if it shows an A-code or E-code?

No. Most codes put the boiler into lockout, and it will not fire again until reset — and in the case of a genuine underlying fault, will lock out again shortly after. Overheat, false-flame, and flue-related codes in particular should not be treated as safe to keep resetting; they need a Gas Safe registered engineer to diagnose before the boiler goes back into regular use.

Why doesn't the code I've found online match the code on the boiler in front of me?

Because Vokèra uses genuinely different code schemes across its ranges, not just different meanings for the same scheme. The majority of the range (Compact, Linea, standard Mynute) uses two-digit A-codes; the Mynute i-series adds AL-prefixed codes for pressure faults; the Evolve range uses a separate E0-prefixed scheme where, for example, E10 means flame lockout — not the same fault as A04's low pressure. Always confirm the range and consult the chart specific to the model in front of you — printed inside the casing on most units, or in that model's installation and servicing instructions.

How much does it typically cost to fix common Vokèra faults?

Indicative part costs, excluding labour: pressure sensor £25–£50; NTC thermistor £15–£30; ignition electrode £20–£40; gas valve £120–£220; pump £120–£250; PCB £200–£350. Labour typically adds £80–£150 depending on diagnosis time and region. **** — costs vary by supplier and model. Always quote diagnosis and repair separately.

Regulations & Standards

• Gas Safety (Installation and Use) Regulations 1998 — all work on gas boilers, including fault diagnosis and repair, must be carried out by a Gas Safe registered engineer

• Building Regulations Part J (England & Wales) — combustion appliance installation and flue requirements

• Building Regulations Part L — conservation of fuel and power; relevant to boiler replacement and control upgrades

• BS 7671 (IET Wiring Regulations) — applicable to any electrical work associated with repair, such as PCB replacement or rewiring

• BS 7593:2019 — treatment of water in domestic hot water central heating systems; relevant when recommending a powerflush or inhibitor treatment for sludge-related faults

• Benchmark Commissioning Checklist — should be reviewed on any callout; incomplete commissioning records are a useful early indicator of a boiler with a history of poor installation

• Gas Safe Register — statutory register for gas engineers in Great Britain

• Vokèra UK — product and service information — check model-specific manuals and fault code charts before diagnosis

• HSE — Gas Safety — statutory guidance on gas appliance safety

• Vokèra Mynute i20 installation and servicing manual — manufacturer fault code table used to verify the A-code scheme in this article

• Heatable — boiler fault code guides — general condensing boiler fault category reference

• vaillant — Vaillant ecoTEC F-code diagnosis, comparable fault categories

• baxi — Baxi boiler error codes

• no hot water but heating works — no hot water diagnostic pathway

• boiler loses pressure repeatedly — recurring low-pressure diagnosis

• condensate pipe frozen boiler lockout — frozen condensate diagnosis and prevention