Alpha E-Tec NXS Fault codes & diagnostics

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

System Natural Gas 2023-present
GC Numbers 41-532-5341-532-5441-532-55
Download the Alpha E-Tec NXS 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.
2 Emergency 21 High 8 Medium
Just want the most common Alpha E-Tec NXS faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 31 documented codes

Tap any card for details

01

Your boiler has tried to light several times but cannot detect a flame, causing the system to lock out for safety.

High DIY-safe £100-280

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. If you have a prepay meter, ensure you have sufficient credit
  3. Attempt to reset the boiler by turning the selector switch to the 'R' position for five seconds
  4. Check if other gas appliances, like a hob, are working to confirm gas supply

Parts commonly replaced

  • Ignition electrode
  • Flame sensing probe
  • Gas valve
  • Spark generator

Related codes

Full explanation for 01
02

Your boiler has switched itself off because it has become too hot inside, likely due to a circulation problem or a temporary blockage.

High DIY-safe £100-£250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your system water pressure is between 1.0 and 1.5 bar on the gauge
  3. Press and hold the 'Reset' button for a few seconds to restart the boiler

Parts commonly replaced

  • Overheat Thermostat
  • Boiler Pump
  • Main Heat Exchanger

Related codes

Full explanation for 02
03

Your boiler has shut down because the exhaust gases have become too hot, which is a safety measure to prevent damage to the system.

High Engineer only £120-£350

Parts commonly replaced

  • Flue NTC sensor
  • Main heat exchanger
  • Burner electrodes

Related codes

Full explanation for 03
04

Your boiler has detected an electrical problem with the component that controls the gas flow, causing the system to shut down for safety.

High Engineer only £140-£320

Parts commonly replaced

  • Gas Valve
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for 04
05

Your boiler has detected a problem with the internal sensor that monitors the temperature of the water heading to your radiators, causing the system to stop running as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Flow NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 05
06

Your boiler is having trouble measuring the temperature of your hot water, which usually means it cannot provide a consistent hot shower.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW NTC thermistor (temperature sensor)
  • Wiring harness

Related codes

Full explanation for 06
08

Your boiler has been manually reset too many times in a short period and has locked itself for safety reasons.

High DIY-safe £0-120

What to check first

  1. Turn off the electrical power supply to the boiler at the fused spur switch
  2. Wait for at least 30 seconds
  3. Turn the power back on to clear the software lockout and allow a new reset attempt

Parts commonly replaced

  • No parts usually required
  • Ignition Electrode
  • Gas Valve

Related codes

Full explanation for 08
10

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

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (braided silver hose) underneath or near the boiler
  2. Slowly open the tap or taps on the filling loop until you hear water moving
  3. Watch the pressure gauge and close the taps once the needle reaches between 1 and 1.5 bar

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure switch

Related codes

Full explanation for 10
12

Your boiler has detected an issue with the sensor that monitors the temperature of the cold water entering the unit, which might cause inconsistent hot water temperatures.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Inlet Sensor (NTC thermistor)
  • Sensor wiring harness

Related codes

Full explanation for 12
15

Your boiler's internal settings do not match the way it was piped up, which means the system cannot safely regulate itself and has stopped running.

High Engineer only £70-130

Parts commonly replaced

  • Main PCB (software configuration)
  • Control Panel

Related codes

Full explanation for 15
Showing 11–20 of 31
16

Your boiler has stopped working because the internal fan is not communicating correctly with the main control board.

High Engineer only £220-450

Parts commonly replaced

  • Extraction Fan
  • Main PCB
  • Wiring Loom

Related codes

Full explanation for 16
20

Your boiler thinks it sees a flame even though it hasn't properly started up yet, which is causing it to shut down for safety.

High Engineer only £90-250

Parts commonly replaced

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

Related codes

Full explanation for 20
23

Your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 23
24

One of the buttons on your boiler's control panel has become stuck or is being pressed down continuously, preventing the system from operating correctly.

Medium DIY-safe £80-220

What to check first

  1. Gently press and release each button on the control panel to see if any feel stuck or 'clicked' in.
  2. Wipe the control panel with a dry, lint-free cloth to ensure no dirt or debris is jamming the buttons.
  3. Restart the boiler by turning the power off at the fused spur switch for 30 seconds and then back on.

Parts commonly replaced

  • Control panel interface
  • Main PCB

Related codes

Full explanation for 24
29

Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust fumes, causing the system to shut down for safety.

High Engineer only £120-190

Parts commonly replaced

  • Flue NTC sensor
  • Wiring harness

Related codes

Full explanation for 29
31

Your boiler has lost its digital connection to your smart thermostat, meaning it no longer knows when to turn the heating on or off.

Medium Engineer only £120-250

Parts commonly replaced

  • Alpha Climatic receiver
  • Communication wiring loom
  • PCB

Related codes

Full explanation for 31
37

Your boiler is struggling because the electrical power it is receiving from your home is not stable or strong enough.

High Engineer only £120-250

Parts commonly replaced

  • PCB
  • Wiring harness
  • Power supply module

Related codes

Full explanation for 37
38

Your boiler has attempted to start but is failing to stay lit, meaning it cannot produce heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

Full explanation for 38
43

Your boiler has stopped working because it cannot maintain a steady flame to heat your water.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 43
45

Your boiler has detected that the water temperature is rising too quickly or there is a significant difference between the water leaving and returning to the boiler, usually caused by a restricted flow.

High Engineer only £120-250

Parts commonly replaced

  • System Filter
  • Pump
  • Diverter Valve

Related codes

Full explanation for 45
Showing 21–30 of 31
47

Your boiler is working at a lower power level than usual to protect itself, meaning your heating or hot water may feel lukewarm.

Medium Engineer only £120-250

Parts commonly replaced

  • Temperature sensors
  • Heat exchanger
  • Main PCB

Related codes

Full explanation for 47
51

Your boiler is struggling to talk to its wireless control unit, which means it may not be receiving instructions to turn your heating or hot water on.

Medium DIY-safe £120-200

What to check first

  1. Check if the batteries in your wireless room thermostat or programmer are flat and replace them if necessary.
  2. Turn the boiler off at the fused spur for 60 seconds, then turn it back on to force a communication reset.
  3. Ensure the wireless receiver unit near the boiler is not obstructed by large metal objects or electrical interference.

Parts commonly replaced

  • RF Receiver unit
  • PCB (Printed Circuit Board)
  • Wireless thermostat

Related codes

Full explanation for 51
60

Your boiler's water circulation pump has stopped working, meaning the system cannot move heated water to your radiators or taps.

High Engineer only £200-350

Parts commonly replaced

  • Circulation pump
  • Pump wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 60
61

Your boiler's water pump is struggling because trapped air bubbles are preventing it from circulating heat through your home.

Medium Engineer only £120-220

Parts commonly replaced

  • Automatic air vent
  • System pump
  • System pressure relief valve

Related codes

Full explanation for 61
70

Your boiler has detected that the water returning to the system is hotter than the water leaving it, which indicates a sensor confusion or a potential blockage in the internal flow.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Central Heating Return Sensor
  • PCB

Related codes

Full explanation for 70
75

Your boiler is struggling to accurately read the temperature of the water circulating through your heating system, so it has shut down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness

Related codes

Full explanation for 75
76

Your boiler is struggling to accurately read the temperature of the water flowing through your system, so it has stopped working to prevent potential overheating.

High Engineer only £150-250

Parts commonly replaced

  • Return/Flow NTC sensor
  • Wiring harness

Related codes

Full explanation for 76
E03

Your boiler has detected that the exhaust gases are becoming dangerously hot and has shut itself down to prevent damage or safety risks.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue sensor
  • Primary heat exchanger
  • Pump

Related codes

Full explanation for E03
E12

Your boiler is struggling to accurately detect the temperature of your hot water cylinder, which means it may not be heating your water correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • Cylinder NTC sensor
  • Wiring harness

Related codes

Full explanation for E12
E20

Your boiler has detected a flame when it shouldn't be there, which has triggered a safety shutdown to prevent any risk.

Emergency Engineer only £150-300

Parts commonly replaced

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

Related codes

Full explanation for E20
Showing 31–31 of 31
E38

Your boiler is struggling to keep the flame lit and is automatically trying to restart itself, but it is unable to maintain a stable burn.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification probe
  • Ignition lead
  • Gas valve

Related codes

Full explanation for E38
Status & diagnostic codes

23 operating states & engineer diagnostics

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

d0 Diagnostic Your boiler is displaying a code that does not correspond to a recognised error, which often indicates a temporary software glitch or a communication issue between the system components. d1 Diagnostic Your boiler has detected an issue with the flame during operation and has shut down for safety to prevent gas buildup. d2 Diagnostic Your boiler is simply reporting that it is monitoring the temperature of the water currently being heated to circulate around your radiators. d3 Diagnostic Your boiler's internal management system has encountered an undefined error code, meaning the control board does not recognise a specific fault. d4 Diagnostic Your boiler is signalling that the temperature setting for your radiators is currently being adjusted or is not being correctly detected. d5 Diagnostic Your boiler is simply indicating the current temperature setting for your hot water, which is a normal status display rather than a fault. d6 Diagnostic Your boiler is struggling to read the outdoor temperature sensor, so it is defaulting to a standard internal temperature setting to keep your home warm. d7 Diagnostic Your boiler is struggling to accurately read the temperature of your hot water cylinder, which may result in your water being too cold or too hot. d8 Diagnostic Your boiler is struggling to read the temperature of the water returning from your radiators, which prevents it from heating your home efficiently. d9 Diagnostic Your boiler is simply displaying a log of its past performance history rather than indicating a current functional problem. d10 Diagnostic Your boiler's memory log of previous errors has been cleared or accessed, but this is not a sign of a current mechanical breakdown. d11 Diagnostic Your boiler's electronic control system is experiencing an undefined internal communication error that is preventing it from operating correctly. d12 Diagnostic Your boiler is reporting that the internal pump, which moves water around your heating system, is currently switched off. d13 Diagnostic Your boiler's electronic brain is experiencing an internal communication error that prevents it from starting up correctly. d14 Diagnostic Your boiler is struggling to detect water flowing through your heating system, which is preventing it from safely turning on your radiators. d15 Diagnostic Your boiler is struggling to maintain the correct internal airflow needed to run safely and efficiently. d16 Diagnostic Your boiler has detected an issue with the sensor that monitors the temperature of the gases leaving your flue, meaning it has safely shut down to prevent potential overheating. d17 Diagnostic Your boiler is struggling to accurately read or control the temperature of the water circulating through your radiators. d18 Diagnostic Your boiler is currently running a special programme designed to slowly dry out new floor screed, which is a normal process and not a fault. d19 Diagnostic Your boiler is simply showing you its internal software information and this is not a sign of a mechanical fault or breakdown. d20 Diagnostic Your boiler is displaying a code that is not currently assigned to a specific function or fault, often indicating a potential internal communication or software glitch. d21 Diagnostic Your boiler's internal computer has encountered an undefined error code that does not correspond to a specific known fault in the system. d22 Diagnostic Your boiler is simply reminding you that your annual safety service is now due based on the time since your last inspection.
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