Alpha Pro Tec Plus Fault codes & diagnostics

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

RegularSystem Natural GasLPG 14.6-33.7 kW Discontinued
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Severity at a glance

Each cell = one fault code. Hover to identify.
32 High 2 Medium 1 Low

All 35 documented codes

Tap any card for details

0A1

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

High DIY-safe £120-250

What to check first

  1. Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property
  2. Check if your gas meter has credit
  3. Press the reset button on the boiler control panel

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 DIY-safe £120-250

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar).
  3. Press and hold the reset button for 2-5 seconds to see if the system restarts.

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 DIY-safe £100-250

What to check first

  1. Turn the boiler power off at the fused spur switch (the wall switch).
  2. Wait for at least 15 to 30 minutes to allow the internal timer to clear.
  3. Turn the power back on and see if the fault has cleared, but do not press reset again if a different fault code appears.

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 DIY-safe £120-220

What to check first

  1. Check if other appliances in your home are struggling or if there is a local power cut
  2. Ensure the boiler's electrical fused spur switch is fully turned on
  3. Reset the boiler by turning the selector switch to the 'R' position for 5 seconds

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.

Medium Engineer only £100-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

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 its control system, which prevents it from firing up correctly.

High Engineer only £120-250

Parts commonly replaced

  • Control PCB
  • Communication cable
  • Cascade interface module

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 The boiler is currently displaying its current central heating temperature setting rather than an actual fault. P02 Diagnostic Your boiler is currently undergoing a routine technical adjustment to limit its maximum water temperature to ensure safe and efficient operation. P03 Diagnostic Your boiler is struggling to maintain a steady temperature and is turning itself off and on too frequently to prevent overheating. P04 Diagnostic Your boiler is temporarily waiting between heating cycles to protect itself from unnecessary wear and tear. P05 Diagnostic Your boiler is currently waiting for internal temperatures to balance out before it starts up, which is a normal part of its operating process. P06 Diagnostic Your boiler is struggling to increase the temperature of your radiators as quickly as it expects to, so it has paused operation to prevent any internal damage. P07 Diagnostic Your boiler is struggling to circulate water correctly after it has finished heating, which may indicate a blockage or a mechanical issue with the water pump. P08 Diagnostic Your boiler has detected that it is running at its maximum heat capacity, which is likely due to an issue with the sensors or the internal control system. P09 Diagnostic Your boiler is struggling to maintain its lowest power setting, which typically indicates a mismatch between the gas pressure and the burner's ability to run efficiently. P10 Diagnostic Your boiler has detected that the water is not circulating fast enough through the system to heat your home safely. P11 Diagnostic Your boiler is displaying a status alert indicating that an internal moisture protection setting has been activated to protect sensitive electrical components. P12 Diagnostic Your boiler is currently operating in a specialized communication mode designed for multiple connected units, which is preventing it from heating your home normally. P13 Diagnostic Your boiler's computer is struggling to recognise the power settings configured during installation, which prevents it from firing up safely. P14 Diagnostic Your boiler has detected an issue with the outdoor weather sensor that tells it how hard to work based on the temperature outside. P15 Diagnostic Your boiler is receiving an incorrect or inconsistent signal from the weather sensor installed outside your home, which may affect how the heating adjusts to the outside temperature. P16 Diagnostic Your boiler is having trouble correctly measuring or reaching the requested temperature for your hot water taps. P17 Diagnostic Your boiler is struggling to provide hot water because it has detected a problem with how it manages or senses the water flow. P18 Diagnostic Your boiler is struggling to keep your hot water at the correct temperature, which may result in lukewarm or inconsistent hot water taps. P19 Diagnostic Your boiler is simply performing a routine cooling process to move leftover heat away from the system after you last used the hot water tap. P20 Diagnostic Your boiler is currently running at its maximum capacity to heat your hot water, which is a normal operational state rather than a sign of a fault. P21 Diagnostic Your boiler is struggling to control the temperature of your hot water, which may cause your taps to run cold or fluctuate in temperature. P22 Diagnostic Your boiler has detected that the temperature of the water being heated for your taps and shower is not being measured or managed correctly by the internal sensors. P23 Diagnostic Your boiler is struggling to accurately measure the temperature of the water being heated for your taps and shower, likely due to a faulty sensor. P24 Diagnostic Your boiler is struggling to maintain the correct temperature for your hot water, which usually means it is taking longer than expected to heat up. P25 Diagnostic Your boiler has detected that the internal fan is spinning faster than it should, so it has safely shut down to prevent damage. P26 Diagnostic Your boiler is struggling to push air through its system correctly, so it has stopped working to keep your home safe. P27 Diagnostic Your boiler is struggling because the internal water pump is not moving water fast enough to keep the system running safely. P28 Diagnostic Your boiler is struggling to get the internal water pump moving correctly when it tries to start up, which prevents the heating system from firing safely. P29 Diagnostic Your boiler is having trouble sensing the temperature of your hot water, which may cause your hot water to run cold or behave inconsistently. P30 Diagnostic Your boiler is failing to ignite because it cannot detect the correct airflow required to burn fuel safely. P31 Diagnostic Your boiler's control panel or display screen is experiencing a communication error, meaning the main brain of the unit cannot talk to the interface you use to change settings. P32 Diagnostic Your boiler is currently set to a heating temperature that is too low for the system to function correctly. P33 Diagnostic Your boiler has detected that the external conditions are cold enough to risk freezing, so it is running a safety protection mode to keep its internal components from icing up. P34 Diagnostic Your boiler has detected that the external temperature has dropped low enough to trigger its automatic frost protection system for the connected heating circuit. P35 Diagnostic Your boiler is temporarily waiting to start because it is part of a larger heating system setup where multiple units are programmed to ignite in a specific sequence to avoid overloading the system. P36 Diagnostic Your boiler is struggling to accurately measure its internal water temperature, so it has stopped heating to prevent potential damage. P37 Diagnostic Your boiler is receiving an invalid or missing control signal from an external device, such as a smart thermostat or building management system, preventing it from heating correctly. P38 Diagnostic Your boiler is having trouble communicating with the sensors that monitor the temperature of the water circulating through your radiators.