Alpha Pro Tec 24 Fault codes & diagnostics

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

Combi Natural Gas 24 kW Discontinued
Download the Alpha Pro Tec 24 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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Severity at a glance

Each cell = one fault code. Hover to identify.
33 High 1 Medium 1 Low

All 35 documented codes

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0A1

Your boiler is failing to light the burner, meaning it cannot provide you with any heating or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Gas valve
0A2

Your boiler is failing to detect a flame, so it has safely shut down to prevent the release of unburnt gas.

High Engineer only £120-250

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Printed Circuit Board (PCB)

Related codes

0A3

Your boiler has switched itself off because it has detected dangerously high temperatures, likely caused by a disruption in the flow of water circulating through your radiators.

High Engineer only £120-250

Parts commonly replaced

  • Overheat thermostat
  • Central heating pump
  • System filter
0A5

Your boiler has detected that the internal fan responsible for safely removing exhaust gases is not spinning at the correct speed, causing the system to stop for safety reasons.

High Engineer only £150-350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Printed Circuit Board (PCB)
0A7

Your boiler has detected that the exhaust gases are becoming dangerously hot, so it has safely shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Primary heat exchanger
  • Flue gas sensor
  • Pump
0A9

Your boiler has detected an electrical fault in the system that controls the gas supply, meaning it cannot safely start up to provide heat or hot water.

High Engineer only £150-250

Parts commonly replaced

  • Gas valve
  • PCB (Printed Circuit Board)
  • Wiring harness

Related codes

0A15

Your boiler's temperature sensors are giving conflicting readings, causing the system to stop operating to prevent potential damage.

High Engineer only £120-200

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

0A16

Your boiler is struggling to heat the water quickly enough, so it has stopped working to prevent itself from overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow temperature sensor
  • Central heating pump
  • Diverter valve

Related codes

0A17

Your boiler is struggling to detect the expected temperature increase in the water flowing back to it, likely due to a circulation or sensor issue.

High Engineer only £150-300

Parts commonly replaced

  • Return temperature sensor
  • Central heating pump
  • PCB

Related codes

0A18

Your boiler has detected an unusual and rapid change in water temperature, causing it to shut down for safety reasons to prevent overheating.

High Engineer only £150-250

Parts commonly replaced

  • NTC Sensor
  • Flow and return wiring harness
  • Primary Heat Exchanger

Related codes

Showing 11–20 of 35
0A21

Your boiler's central control computer has encountered an internal error and cannot communicate properly, meaning the system has shut down for safety.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness
0A30

Your boiler is struggling to detect the flow of water because of a faulty electrical connection inside the unit, meaning it will likely refuse to heat your water.

High Engineer only £120-220

Parts commonly replaced

  • Flow sensor
  • Wiring harness

Related codes

0A31

Your boiler has detected that a temperature reading from its internal water system is not what it expects, meaning it has safely shut down to prevent damage.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness
  • Printed Circuit Board (PCB)
0A37

Your boiler is experiencing a generic system error that is not linked to a specific recognized fault, often indicating a temporary electronic hiccup.

Medium Engineer only £90-180

Parts commonly replaced

  • PCB
  • Wiring harness
0A43

Your boiler is currently unable to read the water temperature correctly because of a faulty internal sensor connection, which has caused it to stop heating your home as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness
0A44

Your boiler is struggling to accurately measure the temperature of the water returning to it, which causes it to stop operating to stay on the safe side.

High Engineer only £120-220

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness
0A80

Your boiler is having trouble communicating with its internal temperature sensors, which means it cannot accurately measure how hot the water is and has stopped working as a safety precaution.

High Engineer only £120-220

Parts commonly replaced

  • NTC Sensor
  • Wiring harness
0E2

Your boiler is unable to confirm that the burner has successfully lit, so it has safely shut itself down to prevent gas buildup.

High Engineer only £120-250

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • PCB

Related codes

0E8

Your boiler has detected an issue with the system that lights the flame, meaning it cannot safely ignite to produce heat or hot water.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB (Printed Circuit Board)

Related codes

0E13

Your boiler has locked itself for safety after too many unsuccessful restart attempts in a short period of time.

High Engineer only £100-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Showing 21–30 of 35
0E25

Your boiler's central control computer is experiencing a critical internal failure and has stopped the system from operating to prevent further damage.

High Engineer only £250-450

Parts commonly replaced

  • Main printed circuit board (PCB)
0E32

Your boiler has detected a faulty connection in the part that measures the temperature of your hot water, which is preventing it from heating your taps correctly.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC thermistor

Related codes

0E33

Your boiler is struggling to detect the temperature of the water being heated for your taps, which means it has safely shut down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • DHW NTC thermistor
  • Wiring harness

Related codes

0E34

Your boiler is struggling because the electricity supply it is receiving is weaker than it should be.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
0E37

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

High DIY-safe £0-£100

What to check first

  1. Locate the internal filling loop, which is usually a small silver braided hose or a plastic key located underneath the boiler.
  2. Open the filling valve slowly to let water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close the valve tightly to stop the flow of water and ensure the boiler resets itself automatically.

Parts commonly replaced

  • Pressure relief valve
  • Expansion vessel
  • Filling loop

Related codes

0E45

Your boiler has detected an issue with the sensor that monitors the temperature of the gases leaving your system, which is preventing it from firing up safely.

High Engineer only £120-220

Parts commonly replaced

  • Flue sensor
  • Wiring harness
0E46

Your boiler has detected that the exhaust temperature is being measured incorrectly and has shut itself down as a safety precaution.

High Engineer only £150-250

Parts commonly replaced

  • Flue gas temperature sensor
  • Wiring harness

Related codes

0E81

Your boiler's temperature sensors are giving conflicting readings, causing the system to stop operating safely to prevent potential overheating.

High Engineer only £150-250

Parts commonly replaced

  • NTC flow sensor
  • NTC return sensor
  • Wiring harness
0E98

Your boiler is struggling to talk to the control system or other connected units, causing it to pause operations to prevent errors.

High Engineer only £120-250

Parts commonly replaced

  • Communication cable
  • PCB
  • Cascade controller

Related codes

0E99

Your boiler is struggling to talk to another heating unit connected to it, which is preventing the system from operating correctly.

High Engineer only £120-250

Parts commonly replaced

  • Cascade control cable
  • PCB interface module
Showing 31–35 of 35
FE

Your boiler is experiencing a communication error between its internal electronic parts, meaning it has stopped working to prevent further damage.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Control panel module

Related codes

FE94

Your boiler's main control panel is failing to process information correctly, which has caused it to shut down for safety.

High Engineer only £250-400

Parts commonly replaced

  • Display PCB
  • Main Control PCB
FE95

Your boiler is having trouble reading the temperature of the water flowing through your system because of a faulty connection or sensor.

High Engineer only £120-220

Parts commonly replaced

  • External flow temperature sensor
  • Wiring harness / সংযোগ
FE96

Your boiler is struggling to detect the outside temperature, so it is temporarily running on a backup setting to keep your home warm.

Low Engineer only £100-200

Parts commonly replaced

  • External temperature sensor
  • Wiring loom
FE97

Your boiler's internal computer system is currently confused and cannot communicate correctly, meaning the unit will not start until it is digitally reconfigured.

High Engineer only £150-300

Parts commonly replaced

  • Main PCB
  • Display PCB

38 operating states & engineer diagnostics

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

P01 Diagnostic This code is not actually a fault, but an information message indicating that your boiler is currently displaying or adjusting the target temperature for your central heating radiators. P02 Diagnostic Your boiler is currently performing a routine self-check or configuration step to limit the maximum temperature of the water it sends to your radiators. P03 Diagnostic Your boiler is rapidly turning itself on and off because it is struggling to move heat away from the unit effectively. P04 Diagnostic Your boiler is temporarily resting between cycles to protect its internal parts from excessive wear and tear. P05 Diagnostic Your boiler is currently taking a moment to adjust its internal temperature settings before it restarts, which is a normal part of its safety process. P06 Diagnostic Your boiler is currently monitoring how quickly its internal temperature rises while warming your radiators to ensure everything is operating safely. P07 Diagnostic Your boiler is signalling that the internal water pump is running for longer than expected to cool the system down, which usually points to a sensor or flow issue. P08 Diagnostic Your boiler is currently running at its maximum heating capacity and is effectively performing a self-check of its burner system. P09 Diagnostic Your boiler is struggling to operate at its lowest power setting, which typically indicates it is having trouble regulating its burner correctly. P10 Diagnostic Your boiler has detected that the water is not circulating through the heating system quickly enough to operate safely. P11 Diagnostic Your boiler has detected an issue with the internal moisture levels, which is preventing it from firing up correctly. P12 Diagnostic Your boiler is currently running at its absolute lowest power setting as part of a multi-boiler system, which may result in insufficient heating or hot water if it cannot ramp up as required. P13 Diagnostic Your boiler has lost its internal configuration settings and cannot determine the correct power output it should be using to heat your home. P14 Diagnostic Your boiler is struggling to read the temperature from an outdoor sensor, which is causing it to adjust your heating settings unexpectedly. P15 Diagnostic Your boiler is struggling to read the temperature from the outdoor sensor, which helps it adjust your heating based on the weather. P16 Diagnostic Your boiler is struggling to accurately read or control the temperature of your hot water supply. P17 Diagnostic Your boiler is struggling to provide hot water properly, which usually indicates an issue with the sensor that detects when you have turned on the tap. P18 Diagnostic Your boiler is struggling to maintain the correct temperature for your hot water supply, which may cause your taps or shower to run cold or fluctuate in temperature. P19 Diagnostic Your boiler is currently running a routine process to cool down after you have used the hot water taps, and it should clear itself automatically once finished. P20 Diagnostic Your boiler is operating at its maximum setting for hot water, which is a status message rather than a breakdown. P21 Diagnostic Your boiler is struggling to maintain a low flame setting while heating your domestic hot water, which may cause the water temperature to fluctuate or the system to shut down. P22 Diagnostic Your boiler is struggling to accurately detect the temperature of the hot water it is producing. P23 Diagnostic Your boiler is struggling to accurately measure the temperature of the hot water it is producing, which is likely preventing it from heating your taps or shower correctly. P24 Diagnostic Your boiler is struggling to maintain a consistent temperature for your hot water, likely because it is taking too long to reach the requested setting. P25 Diagnostic Your boiler has detected that the internal exhaust fan is spinning too fast, so it has safely shut down to prevent any damage. P26 Diagnostic Your boiler is struggling to push air through the system correctly, which is preventing it from lighting safely. P27 Diagnostic Your boiler has detected that the water pump inside is struggling to move water around your heating system effectively. P28 Diagnostic Your boiler is struggling to circulate water properly when it tries to start up, which is preventing it from firing up your heating or hot water. P29 Diagnostic Your boiler is struggling to detect the temperature of the water for your taps and shower, which means you may have inconsistent hot water. P30 Diagnostic Your boiler is struggling to get the internal fan spinning at the right speed to safely clear exhaust gases, so it has stopped working to prevent a safety risk. P31 Diagnostic Your boiler's electronic control panel is experiencing a communication or display error, meaning the system cannot correctly show or process information. P32 Diagnostic Your boiler has detected that the central heating temperature setting has been adjusted below its allowed minimum level. P33 Diagnostic Your boiler has detected that the temperature is low enough to risk freezing, so it is activating a protective mode to prevent damage to the pipes. P34 Diagnostic Your boiler has detected that the external frost protection mode has ended and is automatically resetting itself. P35 Diagnostic Your boiler is momentarily pausing its start-up sequence to prevent multiple units from firing at the exact same time. P36 Diagnostic Your boiler is struggling to read its own internal water temperature accurately, so it has stopped working to prevent potential overheating. P37 Diagnostic Your boiler is receiving an invalid or missing control signal from an external device like a smart thermostat or energy management system, preventing it from starting correctly. P38 Diagnostic Your boiler is having difficulty reading the water temperature in your heating system, which has caused it to stop working to prevent overheating.