Vokera Unica 24HE Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2006-2012 Discontinued

Replaced by: Unica i

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17 High
Just want the most common Vokera Unica 24HE faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 17 documented codes

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10

Your boiler has failed to ignite, which means it cannot provide heat or hot water because it isn't successfully lighting a flame.

High DIY-safe £120-280

What to check first

  1. Check if other gas appliances, like a cooker hob, are working to confirm gas supply.
  2. Check that your gas meter has credit if you have a pre-payment meter.
  3. Reset the boiler by turning the mode selector switch to the 'Reset' position for a few seconds and then back to 'On'.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Printed Circuit Board (PCB)
Full explanation for 10
AL10

Your boiler has failed to light because either the gas didn't ignite or a sensor has detected that the condensate drainage pipe is blocked.

High DIY-safe £80-250

What to check first

  1. Check if your gas supply is active (e.g. check other gas appliances or your prepayment meter balance).
  2. Inspect the white plastic pipe leading outside for ice or blockages; if frozen, gently defrost it with warm (not boiling) water.
  3. Turn the mode selector dial to the 'RESET' position for a few seconds, then back to your desired setting.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Condensate Trap or Pipework
Full explanation for AL10
AL20

Your boiler has sensed that it is starting to overheat and has shut itself down as a safety precaution.

High DIY-safe £90-180

What to check first

  1. Turn the mode selector switch to the OFF/RESET position, wait a few seconds, then move it back to the 'Hot Water' or 'Heating' position.
  2. Check that your radiator valves are open and not blocked by furniture.
  3. Ensure there is enough pressure in the system by checking the gauge is between 1 and 1.5 bar.

Parts commonly replaced

  • Limit Thermostat (High Limit Sensor)
  • Circulating Pump
  • Main Heat Exchanger (if scaled up)

Related codes

Full explanation for AL20
AL21

Your boiler has detected an issue with an external safety device or thermostat connection, causing it to stop running for safety.

High Engineer only £90-250

Parts commonly replaced

  • External Limit Thermostat
  • Control PCB
  • Wiring Harness

Related codes

Full explanation for AL21
AL26

Your boiler has shut down because the water returning to the unit is too hot, which usually means heat isn't being distributed around your home properly.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves (TRVs) are fully open
  2. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  3. Reset the boiler by turning the mode selector dial to 'OFF/RESET' and back to 'ON'

Parts commonly replaced

  • Circulation Pump
  • Return NTC thermistor
  • Secondary Heat Exchanger

Related codes

Full explanation for AL26
AL28

Your boiler has detected that heat is flowing in the wrong direction or the sensors are reading temperatures incorrectly, causing the system to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

  • Flow thermistor
  • Return thermistor
  • NTC sensor wiring

Related codes

Full explanation for AL28
AL34

Your boiler has stopped working because the fan that clears away waste gases is not spinning at the correct speed or its signal isn't being picked up by the system.

High Engineer only £180-350

Parts commonly replaced

  • Fan motor
  • Main Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for AL34
AL40

Your boiler has detected that the water pressure in the central heating system is too low to operate safely and has shut down.

High DIY-safe £0-160

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose with one or two black taps underneath the boiler.
  2. Slowly open both taps (or one if there is only one) until you hear water flowing into the boiler.
  3. Watch the pressure gauge on the front of the boiler and close the taps once the needle reaches between 1.0 and 1.5 bar.
  4. Press the Reset button on the boiler control panel to clear the fault code.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for AL40
AL41

Your boiler has stopped working because the water pressure in the system has dropped too low to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (a flexible silver hose) underneath or near the boiler.
  2. Open the one or two small valves on the loop slowly until you hear water moving.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.
  4. Reset the boiler using the mode selector dial.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for AL41
AL52

Your boiler's internal computer has encountered a memory or software error and can no longer control the heating properly.

High Engineer only £250-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)

Related codes

Full explanation for AL52
AL55

Your boiler’s internal control board has lost its identity settings and needs to be reconfigured by a professional.

High Engineer only £100-280

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Configuration Jumper

Related codes

Full explanation for AL55
AL60

Your boiler has detected a problem with the sensor that monitors hot water temperature, which may result in no hot water or inconsistent temperatures.

High Engineer only £90-160

Parts commonly replaced

  • DHW Thermistor (NTC Sensor)
  • Wiring harness

Related codes

Full explanation for AL60
AL71

Your boiler has detected an issue with the sensor that measures the temperature of the water leaving the unit, meaning it cannot safely regulate heat.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for AL71
AL73

Your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, which is preventing it from running safely.

High Engineer only £90-160

Parts commonly replaced

  • Return thermistor (NTC sensor)
  • Wiring harness
  • Control board

Related codes

Full explanation for AL73
AL74

Your boiler has detected that the water temperature is changing too quickly or inconsistently, causing it to shut down for safety.

High DIY-safe £120-280

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Bleed all radiators to remove trapped air

Parts commonly replaced

  • Temperature thermistor (NTC sensor)
  • Circulation pump
  • Main heat exchanger

Related codes

Full explanation for AL74
AL79

Your boiler has shut down because it detected that the water inside has become dangerously hot or overheated.

High DIY-safe £100-£350

What to check first

  1. Turn the boiler off and wait 30 minutes for it to cool down.
  2. Check that all radiator valves are fully open to allow water to circulate.
  3. Press the 'Reset' button on the front control panel.
  4. Ensure the system pressure gauge is between 1 and 1.5 bar.

Parts commonly replaced

  • Circulation Pump
  • NTC Temperature Sensor
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for AL79
Low-pressure

Your boiler has stopped working because the water pressure inside the system has dropped too low to allow it to run safely.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath the boiler.
  2. Slowly open the one or two small valves on the ends of the pipe until you hear water flowing.
  3. Watch the pressure gauge and close the valves tightly once the needle reaches between 1 and 1.5 bar.

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure sensor
Full explanation for Low-pressure