Vokera Compact 29A Fault codes & diagnostics

12 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 2013-present
GC Number 47-364-18
Download the Vokera Compact 29A manualThe official installation and service manual (PDF), the document these fault codes were read from. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 9 High 2 Low
Fault codes

All 12 documented codes

Tap any card for details

_St

Your boiler has entered a temporary standby mode, which often happens if the system is waiting for the room thermostat to request heating or a hot tap to be opened.

Low DIY-safe

What to check first

  1. Check your room thermostat is turned up high enough to request heat
  2. Ensure your heating programmer is set to 'ON'
  3. Check if the boiler begins working once you turn on a hot water tap
Full explanation for _St
A01

Your boiler has failed to light the flame needed to produce heat or hot water, and it has locked itself out for safety.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for A01
A02

Your boiler has detected that it is running too hot and has safely shut itself down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

  • Limit thermostat
  • NTC thermistor
  • Pump
  • Heat exchanger

Related codes

Full explanation for A02
A03

Your boiler is struggling to detect that the internal fan, which clears exhaust gases, is spinning correctly.

High Engineer only £150-£250

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for A03
A04

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

High DIY-safe £80-150

What to check first

  1. Locate the filling loop (a flexible metal hose) underneath your boiler or near your airing cupboard.
  2. Open the valves on the filling loop slowly to let water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually between 1 and 1.5 bar).
  4. Close both valves tightly to stop the flow of water.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Filling loop

Related codes

Full explanation for A04
A06

Your boiler is struggling to detect the temperature of your hot water, so it has stopped providing it to prevent the system from overheating.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC thermistor sensor
  • Wiring harness

Related codes

Full explanation for A06
A07

Your boiler is not reading its internal water temperature correctly, causing it to shut down to prevent overheating.

High Engineer only £120-180

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring harness

Related codes

Full explanation for A07
A08

Your boiler is struggling to accurately read the temperature of the water returning to it, meaning it cannot reliably heat your home or water.

High Engineer only £120-200

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness

Related codes

Full explanation for A08
A09

Your boiler has detected an issue with the sensor that monitors the temperature of the gases leaving your flue, causing it to shut down for safety.

High Engineer only £120-220

Parts commonly replaced

  • Flue thermistor
  • Wiring harness

Related codes

Full explanation for A09
A11

Your boiler has detected a flame inside the unit when it was supposed to be turned off, so it has safely shut itself down to prevent a hazard.

Emergency Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • PCB (Printed Circuit Board)
  • Flame rectification electrode

Related codes

Full explanation for A11
A77

Your boiler's internal computer is receiving an unexpected temperature reading from a sensor, which has caused it to stop working for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • NTC temperature sensor
  • Wiring harness
  • Printed Circuit Board

Related codes

Full explanation for A77
Status & diagnostic codes

8 operating states & engineer diagnostics

Not faults — these are normal operating states. Tap to expand.

P blinking Status Your boiler is simply performing a standard procedure to keep a small amount of water warm, allowing it to provide hot water to your taps more quickly. _CL Diagnostic Your boiler has reached its programmed time limit for a scheduled service and is prompting you to book a professional engineer to check the system. ACO Diagnostic Your boiler has reached its programmed time limit and is simply reminding you that a routine safety service is now due. Adj Diagnostic Your boiler is currently recalibrating its internal settings to ensure it operates efficiently after a recent change or power cycle. Flame ON Status Your boiler is currently running normally and has detected that the burner flame is lit. Hours Status Your boiler is perfectly healthy and is simply resting until you turn on a tap or adjust your heating. Purge cycle mode active Status Your boiler is currently running a self-startup routine to clear air from the system and is not actually experiencing a fault. Service operation Diagnostic Your boiler is simply reminding you that it is due for its annual safety check and maintenance service.
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