Vokèra boiler error codes
11 codes that Vokèra publishes for its boilers, each with what it means, the likely cause, what you can safely check and when to call a Gas Safe registered engineer. Tap your code:
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone. Anything else is for a Gas Safe registered engineer. If you smell gas, call the National Gas Emergency Service on 0800 111 999. Codes that need one are marked Gas Safe engineer.
Read this first
Vokèra prints the fault codes of the Vision C combi in the users’ part of its combined users’, installation and servicing instructions. Each code is either Final — the boiler stays off until it is reset — or Temporary, clearing itself when the cause goes. Before resetting, Vokèra asks you to check the action the table gives for your code, and to wait two minutes. Several codes cover more than one fault (A07, for example, is a flow thermistor fault, a flow over-temperature or a temperature difference); the table’s actions for thermistors, wiring and the fan are the engineer’s.
A04 Water pressure too low
- What it means
- Insufficient system water pressure. Final: the boiler stays off.
- Likely cause
- Water lost from the heating system.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Read the gauge: with the boiler off and cooled, it should read 1 to 1.5 bar.
- Top up: attach the filling loop to both filling valve connections (usually beneath the boiler), open the filling valve slowly until you hear water entering, close it at 1 to 1.5 bar, then remove the loop.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If the system regularly needs topping up, Vokèra says it may be a leak: ask your installer or a Gas Safe registered engineer to inspect it.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A01 Ignition failure
- What it means
- Ignition failure: the flame was not sensed, or an internal fault. Final.
- Likely cause
- No flame detected at ignition.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A02 Limit thermostat fault
- What it means
- The limit thermostat has operated or failed. Final.
- Likely cause
- Overheating or the limit thermostat itself.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A03 Fan speed signal fault
- What it means
- Fan tacho signal fault: the boiler cannot read the fan’s speed. Final.
- Likely cause
- The fan or its signal wiring.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer. Checking the fan is engineer work.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A06 Hot water thermistor fault
- What it means
- The hot water (DHW) thermistor has a fault. Temporary.
- Likely cause
- The thermistor or its wiring.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call a Gas Safe registered engineer to check the hot water thermistor.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A07 Flow thermistor fault or over-temperature
- What it means
- One of three faults on the flow (primary) side: a thermistor fault (Temporary), a flow over-temperature (Temporary, then Final) or a temperature differential (Final).
- Likely cause
- The flow thermistor or its wiring, overheating, or a temperature difference the boiler does not expect.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer. The thermistor and wiring checks are for the engineer.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A08 Return thermistor fault or over-temperature
- What it means
- One of three faults on the return side: a thermistor fault (Temporary), a return over-temperature (Temporary, then Final) or an inverted temperature differential (Final).
- Likely cause
- The return thermistor or its wiring, overheating, or too little circulation around the heating circuits.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer. Vokèra’s checks for the inverted differential — the pump, and enough circulation round the heating circuits — are for the engineer.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A09 Flue thermistor fault or over-temperature
- What it means
- A flue thermistor or thermistor-counter fault (Temporary), or a flue over-temperature (Final).
- Likely cause
- The flue thermistor or its wiring, or a hot flue.
- What you can safely check
Gas boiler: do only the checks its user manual gives you — read the pressure gauge, top up through the filling loop, press the reset button, thaw a frozen condensate pipe at ground level. Keep the casing on and leave sealed parts alone.
- Wait two minutes, then turn the mode selector knob across the reset position, as the manual describes.
- When to call a Gas Safe registered engineer
- If it will not reset, or you need to reset often, contact your installer or Vokèra Customer Services for a Gas Safe registered engineer. The thermistor checks are for the engineer.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A77 Low temperature thermostat fault
- What it means
- The low temperature thermostat has a fault. Temporary.
- Likely cause
- The low temperature thermostat or its wiring.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call a Gas Safe registered engineer or your installer to check the low temperature thermostat.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
_St Autostop
- What it means
- Autostop. Final.
- Likely cause
- The table names the fault only.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call a Gas Safe registered engineer — the table’s action is “Call engineer”.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
_CL Call for service
- What it means
- Call for service. Temporary at first, then Final.
- Likely cause
- The table names the fault only.
- What you can safely check
Nothing for the owner to check: this one is for a Gas Safe registered engineer.
- When to call a Gas Safe registered engineer
- Gas Safe engineer Call a Gas Safe registered engineer — the table’s action is “Call engineer”.
Source: Vokèra, Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.
A code that is not listed here
Other Vokèra boilers show faults differently: the Compact A, for example, uses red, yellow and green lights instead of codes. For a code not listed, contact your installer or Vokèra Customer Services.
We list only codes the source below states. If your code is not here, it may belong to a model the source does not cover: your model’s manual is the authority.
Related pages
Source
Every code on this page comes from this page, published by Vokèra and read on the date shown. Meanings are written in our own words; nothing is taken from other makes, other models or third-party code sites.
- Vokèra: Vision C high-efficiency combi boiler: users instructions, installation and servicing instructions — fault codes Checked 2026-09-29.