Vokèra Boiler Fault Codes Causes & Fixes

If your Vokèra boiler is showing a fault code, the first thing to know is that these codes are safety messages, not necessarily signs of a major problem. The boiler is telling you what it detected and why it stopped firing. Understanding what each code means helps you decide what you can check yourself and when to call a Gas Safe engineer.

Common Vokera boiler red light issues are often linked to the fault codes below. In many cases a single reset after checking system pressure or the gas supply is all that is needed. In others, professional diagnosis is the only safe path forward.

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How Vokèra Boiler Fault Codes Work

A Vokèra boiler continuously monitors water pressure, temperatures, ignition, airflow, and combustion conditions. Following good vokera boiler maintenance tips for homeowners including annual servicing helps prevent many of these codes from appearing in the first place.

When any monitored value falls outside the safe range, the boiler locks out and displays a fault code to protect key components such as the heat exchanger, burner, and flue system. Different Vokèra models use different code formats:

• A codes: used across the standard Compact, Unica, and Flowmatic ranges
• AL codes: specific to the Mynute series
• E codes: used on the newer Evolve range

The meaning changes slightly by model, but the safety logic is always the same. Sensor fault, repair cost data (2025/2026): thermistor or sensor replacement typically costs £100 to £150; fan or gas valve work runs £250 to £350.

Vokèra “A” Series Fault Codes

A01 / 01 – Ignition Failure

The boiler tried to light but could not detect a stable flame. This is the most common fault code on Vokèra boilers and can be triggered by an interruption to the gas supply, a dirty or worn ignition electrode, a faulty gas valve, or a problem with the flue system.

Before calling anyone out: check that other gas appliances in the property are working. If not, the issue is with the supply rather than the boiler. Check the gas meter is on and, on prepayment meters, that there is credit. Wait two minutes, then try a single reset. If A01 returns immediately or after one firing attempt, do not keep resetting. Contact a Gas Safe engineer to inspect the electrodes, gas valve, and flue.

A02 – Overheat or Limit Thermostat Fault

The safety limit thermostat has detected excessive heat inside the boiler and tripped. The most common causes are a failing or seized circulating pump, trapped air in the radiators, or a blockage restricting water flow through the heat exchanger.

Let the boiler cool fully before doing anything. Bleed all radiators and confirm pressure is between 1.0 and 1.5 bar before attempting a single reset. If overheating happens again after one reset, there is an underlying circulation or pump problem that needs professional investigation.

A11 – False Flame Detected

The boiler’s flame sensor is detecting a signal when the boiler should not be firing. This is a combustion-related safety issue and requires a Gas Safe engineer to check flame sensing components and controls. Do not attempt to resolve this yourself.

A04 / 40 / 41 – Low Water Pressure

System pressure has dropped below the safe operating level. Most Vokèra boilers need 1.2 to 1.5 bar when cold to operate correctly. Top up carefully using the filling loop until the gauge reads 1.2 bar, then attempt a single reset.

If pressure drops again within a few days, there is a leak somewhere in the system or a failing expansion vessel that needs professional attention. Repeated topping up dilutes the system inhibitor and can accelerate internal corrosion over time.

A03 / 03 – Fan or Flue Fault

The boiler cannot confirm safe airflow through the flue. Because the fan controls the safe removal of combustion gases from the property, this code must only be investigated by a Gas Safe engineer. Do not operate the boiler while this code is showing.

A06 – Domestic Hot Water Thermistor Fault

The boiler is not getting a reliable temperature reading for the hot water circuit. This typically causes fluctuating water temperature or a complete loss of hot water. The thermistor (temperature sensor) usually needs replacing by an engineer.

A07 – Primary Flow Thermistor Fault

The boiler is detecting an abnormal flow temperature in the primary heating circuit. This can be linked to restricted circulation, limescale build-up in the heat exchanger, or a faulty sensor. Professional investigation is required.

A08 – Return Thermistor Fault

The return temperature reading is incorrect or excessively high. This is often caused by restricted water flow or a failing return sensor. The pattern of flow temperature versus return temperature tells an engineer a great deal about whether this is a circulation or sensor fault.

A09 – Flue Thermistor Fault

A problem has been detected with flue gas temperature monitoring. Because this relates directly to the safe removal of combustion gases, it always requires professional checks and must not be ignored.

A77 – Low-Temperature Thermostat Fault

The boiler has identified an issue with its internal low-temperature or frost protection thermostat. This is an internal control fault that needs an engineer to test or replace the component.

Vokèra Boiler Status and Service Messages

These are display messages rather than fault codes. Most do not mean the boiler has a problem.

• St – Autostop: the boiler has stopped automatically after detecting a safety condition
• CL – Call for service: the boiler needs professional attention or is due for its annual service
• ADJ – Calibration mode: engineer-only mode; should not appear in normal domestic use
• ACO – Service operation: the boiler is in a dedicated service or testing mode
• Flame on: confirms the burner flame is currently present
• P or flashing P – Preheat active: the hot water preheat function is running
• Hours / standby / off: “Hours” means the boiler has power but is not firing; this usually means it is switched off at the programmer or thermostat

Vokèra Mynute “AL” Fault Codes

AL10 / AL20 / AL21 / AL26 / AL28 / AL34 – General Fault

These codes indicate a general internal fault on Mynute models. A reset may clear a one-off occurrence, but if any of these return after resetting, the boiler has identified an ongoing issue that needs professional diagnosis.

AL40 / AL41 – Low System Pressure

The equivalent of A04 on the Mynute range. Topping up to around 1.2 to 1.5 bar should resolve the immediate lockout. If AL40 or AL41 keeps appearing, persistent pressure loss points to a leak or expansion vessel problem in the system rather than a fault inside the boiler itself.

AL52 / AL55 / AL60 / AL71 / AL73 / AL74 / AL79 – Internal Fault

These codes relate to internal controls or components on the Mynute series. None of them are user-repairable and all require diagnosis by a Gas Safe engineer. If AL74 or AL79 return after a reset, the boiler has identified a persistent issue that needs professional repair.

Vokèra Evolve “E” Fault Codes

E10 – Flame Lockout

The boiler failed to establish a stable flame on the Evolve range. One reset is acceptable after confirming the gas supply is on and other gas appliances are working. If E10 returns after one reset, call a Gas Safe engineer. Do not keep resetting.

E011 – Extraneous Flame

A flame has been detected when the boiler should not be firing. This is a serious combustion safety issue. Turn the boiler off and arrange an urgent engineer visit. Do not reset or attempt to operate the boiler while this code is showing.

E085 / E094 / E095 – Combustion or High Carbon Monoxide Fault

These codes indicate that unsafe combustion conditions have been detected. This is the most urgent category of fault code on a Vokèra boiler. Switch the boiler off immediately, open windows to ventilate the space, and arrange an urgent engineer visit. If you have a carbon monoxide alarm that is sounding, leave the property and call the National Gas Emergency Service on 0800 111 999.

E020 – Overheat Detected

The Evolve has overheated, equivalent to A02 on older models. If this occurs more than once after the boiler has cooled and been bled, circulation or pump problems are the likely cause and need professional investigation.

E030 – Fan Fault

The fan is not operating correctly. Because the fan controls the safe removal of fumes, this code must be checked by a Gas Safe engineer before the boiler is operated again.

E040 / E041 – Water Pressure Transducer Issue

The boiler is detecting incorrect pressure readings. Check the actual pressure gauge first. If the gauge reads correctly between 1.0 and 1.5 bar but the code persists, the pressure sensor (transducer) is likely faulty and needs replacing.

E042 – Water Pressure Transducer Fault

A confirmed fault with the pressure sensor rather than an ambiguous reading. This normally requires the transducer to be replaced by an engineer.

E060 – Hot Water Temperature Probe Fault

The boiler cannot read hot water temperature correctly. This often causes unstable or absent hot water even when the heating circuit is working normally.

E070 – Flow Sensor Over-Temperature

The boiler has detected excessive temperature at the flow sensor, often due to poor water circulation. The cause may be a blocked heat exchanger, a seized pump, or partially closed radiator valves restricting flow.

E077 – Main Heating Thermostat Fault

The thermostat controlling the main heating circuit is not behaving as expected. This is an internal component fault requiring professional diagnosis.

E080 – Return Line Probe Fault

The return temperature sensor is reporting incorrect or unsafe readings. Combined with E070, this pattern often helps an engineer confirm whether a flow restriction or a sensor failure is the root cause.

E090 – Flue Gas Over-Temperature

Flue gases are hotter than they should be. This can indicate a blocked heat exchanger, a flue restriction, or a combustion issue. It needs urgent attention and the boiler should not be operated until an engineer has investigated.

E091 – Clean Primary Heat Exchanger

The boiler has detected reduced heat transfer efficiency, most commonly due to limescale or sludge build-up on the heat exchanger surfaces. An engineer will clean or descale the exchanger. Fitting a magnetic system filter afterwards is strongly recommended to prevent recurrence.

Pressure Out of Range

Low pressure (below 0.5 bar) can usually be topped up via the filling loop to 1.2 bar and then reset. High pressure (above 3 bar) often points to a failing expansion vessel or a pressure relief valve that has been unable to discharge correctly. High pressure must be investigated by an engineer.

Communication Fault – Control Board Error

The boiler’s internal circuit boards are not communicating correctly. This is an electrical or wiring issue requiring professional diagnosis.

E021 / E022 / E023 / E024 / E067 / E088 / E097 – Ionisation Alarm

These codes all relate to flame sensing and combustion stability on the Evolve range. None are user-resolvable beyond a single reset. If any returns after one reset, a Gas Safe engineer must inspect the ionisation probe and combustion settings.

E058 – Main Voltage Error

An electrical supply issue has been detected. Check that the boiler is on a dedicated fused spur rather than a shared circuit. If the supply is confirmed as correct, this needs electrical diagnosis by an engineer.

E065 – Current Modulation Alarm

The boiler has detected a problem with how electrical current is being controlled during operation. This is an internal electronic fault requiring diagnosis.

E086 – Fumes Obstruction Alarm

A possible blockage in the flue or exhaust path has been detected. Switch the boiler off and arrange an urgent inspection. Check the external flue terminal for obvious obstructions such as bird nests, leaves, or ice before the engineer arrives.

What You Can Check Yourself and When to Stop

The following checks are safe for any homeowner:

• Check system pressure when the boiler is cold. If it is below 1.0 bar, top up to 1.2 bar using the filling loop.
• Confirm other gas appliances are working before assuming a boiler fault.
• Attempt a single reset after checking the above two points.
• Bleed all radiators if the code involves overheating or circulation.

Stop and call a Gas Safe engineer if:

• The same fault code returns after one reset.
• The code involves combustion, fumes, fans, or overheating (A02, A03, A09, A11, E011, E020, E030, E085, E086, E090).
• You can smell gas at any point. Leave the property and call 0800 111 999.
• Pressure drops again within a few days of topping up.

For good ongoing system health, following recommended overflow pipe maintenance techniques and keeping an eye on the boiler display helps catch issues before they escalate into full lockouts. You can verify any engineer’s Gas Safe credentials using the Gas Safe Register before booking.

Frequently Asked Questions About Vokèra Boiler Fault Codes

Can cold weather or winter conditions trigger Vokèra fault codes?

Yes. During colder weather, system pressure can dip slightly as water contracts, which sometimes triggers a low-pressure warning. Freezing temperatures can also affect external condensate pipes, causing the boiler to shut down as a safety measure. These issues tend to appear during cold snaps rather than because of an internal fault developing, and are usually resolved by thawing the condensate pipe and resetting.

Do Vokèra boiler fault codes ever clear on their own?

Some do. If the boiler temporarily overheats or detects a short-term issue, it may return to normal once conditions stabilise. Other codes will stay until the boiler is manually reset or the underlying problem is fixed. If the same code returns after a reset, the boiler is telling you something still needs attention.

Can a power cut or electrical issue cause a Vokèra fault code?

Yes. After a power cut or electrical interruption, a Vokèra boiler may display a fault code or fail to restart. Turning the boiler off at the fused spur for 30 seconds and then switching it back on is often enough to restore normal operation. If electrical-related codes appear regularly, this may point to a wiring or control board issue that needs an engineer to investigate.

Is it safe to leave a Vokèra boiler showing an error code?

It depends on the code. Low-pressure codes (A04, AL40) are not immediately dangerous but mean the boiler will not fire. Combustion, fume, or overheating codes (A02, A03, A11, E085, E086) should be treated urgently. If the boiler does not return to normal after basic checks and a single reset, arranging an engineer visit is the safest course of action.

Can low water pressure cause long-term problems if I keep topping up?

Yes. Repeatedly topping up pressure without fixing the underlying cause dilutes the system inhibitor and adds oxygenated water to the circuit, which accelerates internal corrosion and pump wear over time. If your Vokèra frequently shows low-pressure codes, there is almost certainly a slow leak or a failing expansion vessel that needs proper repair rather than repeated topping up.

Will my Vokèra boiler work while an error code is showing?

In most cases, no. When a genuine fault code appears, the boiler has shut itself down to protect components. Heating and hot water will not operate until the issue is resolved. Some display messages (such as “P” for preheat active) are simply status updates and do not stop the boiler from running.

Does regular servicing help prevent error codes?

Significantly, yes. An annual service covers combustion checks, sensor testing, heat exchanger inspection, and cleaning. Many of the fault codes that trigger lockouts develop from issues that would have been caught and resolved at a service. Annual servicing is also a condition of maintaining the Vokèra manufacturer warranty.

Can air in radiators or pipework cause fault codes?

Yes. Trapped air reduces circulation efficiency, which can cause the boiler to overheat and trigger temperature-related fault codes. Bleeding radiators at the start of each heating season and keeping system pressure between 1.0 and 1.5 bar reduces the risk of air-related faults significantly.

Are Vokèra fault codes the same on every model?

Not always. Older Compact and Unica models use “A” codes; Mynute models use “AL” codes; the Evolve range uses “E” codes. The same underlying problem may appear under a different code depending on the model, which is why the guide above is structured by code family.

Is it safe to keep resetting a Vokèra boiler when a fault appears?

A single reset after the basic checks above is reasonable. Repeated resetting hides the underlying problem and can cause additional wear on ignition components. If you find yourself resetting your Vokèra boiler frequently, this is a strong signal that a professional check is needed rather than another attempt at a reset.