Alpha E-Tec Plus 10 / 18 Fault codes & diagnostics

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

System Natural GasLPG 10-18 kW 2019-present

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Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 43 High 6 Medium 4 Low
Just want the most common Alpha E-Tec Plus 10 / 18 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 54 documented codes

Tap any card for details

01

Your boiler has failed to light the gas, meaning it cannot heat your water or radiators.

High DIY-safe £100-280

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob.
  2. Check your gas meter to ensure it has credit or the valve is turned on.
  3. Press and hold the 'R' reset button for 2 seconds to see if the boiler restarts.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Ignition Lead
  • Fan

Related codes

Full explanation for 01
02

Your boiler has shut down because it has detected it is getting too hot, which is usually due to a lack of water flow through the system.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are open to ensure water can move freely.
  2. Check the boiler pressure gauge and top it up to 1.5 bar if it is low.
  3. Attempt to reset the boiler by turning the selector knob to the 'R' position for 5 seconds.
  4. Bleed your radiators to remove any trapped air that might be causing a blockage.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Main Heat Exchanger (if scaled up)

Related codes

Full explanation for 02
03

Your boiler has switched itself off because the waste gases are getting too hot, which is a safety mechanism to prevent internal damage.

Emergency Engineer only £120-350

Parts commonly replaced

  • Flue Thermistor
  • Heat Exchanger cleaning
  • Main Heat Exchanger

Related codes

Full explanation for 03
04

Your boiler has detected an electrical communication problem with the internal gas valve, which means it cannot safely ignite to provide heating or hot water.

High Engineer only £160-£350

Parts commonly replaced

  • Gas Valve
  • Wiring Harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 04
05

Your boiler has detected a problem with the sensor that monitors the temperature of the water leaving the unit, meaning it cannot operate safely or effectively.

High Engineer only £90-160

Parts commonly replaced

  • Flow NTC temperature sensor
  • Wiring harness

Related codes

Full explanation for 05
06

Your boiler has detected a fault with the sensor that manages your hot water temperature, meaning you likely have no hot water or the temperature is inconsistent.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Sensor
  • 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 now locked itself out for safety.

High DIY-safe £0-120

What to check first

  1. Turn the power supply to the boiler off at the fused spur switch
  2. Wait for 30 seconds
  3. Turn the power back on to clear the reset limit

Parts commonly replaced

  • Ignition Electrode
  • Flame Sensing Electrode
  • Gas Valve

Related codes

Full explanation for 08
10

Your boiler has detected that the water pressure is too low for it to operate safely and effectively.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop (usually a silver braided hose underneath the boiler).
  2. Slowly open the valve(s) until you hear water entering the system.
  3. Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.

Parts commonly replaced

  • Primary pressure switch
  • Filling loop valve
  • Expansion vessel

Related codes

Full explanation for 10
12

Your boiler has detected an issue with a temperature sensor that monitors incoming water, which can affect how efficiently it provides hot water.

Low Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) inlet sensor
  • Wiring harness
Full explanation for 12
15

Your boiler’s internal computer is confused because its software settings do not match the physical parts it is trying to control.

High Engineer only £100-280

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

Full explanation for 15
Showing 11–20 of 54
16

Your boiler has stopped working because the internal fan, which safely exhausts fumes, is either not spinning correctly or has lost its electrical connection.

High Engineer only £220-£350

Parts commonly replaced

  • Fan assembly
  • Wiring harness
  • Main PCB

Related codes

Full explanation for 16
20

Your boiler thinks a flame is present even though no gas should be flowing, which is causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Main PCB

Related codes

Full explanation for 20
23

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

High Engineer only £100-180

Parts commonly replaced

  • Return NTC thermistor
  • Sensor wiring harness
  • Main PCB

Related codes

Full explanation for 23
24

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

High DIY-safe £0-120

What to check first

  1. Identify which button on the front panel feels stuck or stiff.
  2. Gently press and wiggle the affected button to see if it pops back out.
  3. Clean the area around the buttons with a dry, soft cloth to remove any sticky residue or dust.
  4. Reset the boiler using the selector switch.

Parts commonly replaced

  • Control panel fascia
  • PCB (if button contact is damaged)

Related codes

Full explanation for 24
25

Your boiler's internal computer has encountered a software glitch and is unable to operate correctly.

High DIY-safe £250-450

What to check first

  1. Turn the selector switch to the 'Reset' position for a few seconds.
  2. Return the switch to the 'On' position to see if the error clears.
  3. Turn the main power supply to the boiler off at the wall, wait one minute, and turn it back on.

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for 25
27

Your boiler is getting too hot too quickly because water isn't moving through the system properly.

High DIY-safe £120-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your boiler pressure is between 1.0 and 1.5 bar on the gauge
  3. Check if any external heating valves or zone valves are stuck closed

Parts commonly replaced

  • Circulation pump
  • Primary heat exchanger
  • Flow/Return thermistors

Related codes

Full explanation for 27
29

Your boiler has detected an issue with the sensor that monitors exhaust gases, and it has shut down as a safety precaution.

High Engineer only £120-£200

Parts commonly replaced

  • Flue NTC sensor
  • Wiring harness
  • Main PCB
Full explanation for 29
31

Your boiler has lost its connection with the remote thermostat or controller, meaning they are no longer talking to each other.

Medium DIY-safe £0-120

What to check first

  1. Check if the batteries in your Alpha Climatic control unit need replacing.
  2. Ensure the controller is within range and has not been moved too far from the boiler.
  3. Reset the boiler by turning the selector switch to the 'RESET' position for 5 seconds.

Parts commonly replaced

  • Batteries
  • Alpha Climatic RF Receiver
  • PCB

Related codes

Full explanation for 31
37

Your boiler is not receiving enough electrical power to turn on or run its functions.

High DIY-safe £0-180

What to check first

  1. Check if there is a local power cut or if other appliances in your home are flickering.
  2. Ensure the boiler's fused spur switch is fully turned on.
  3. Check your home's consumer unit (fuse box) to see if a circuit breaker has tripped and flip it back to 'on'.

Parts commonly replaced

  • Fused spur switch
  • Printed Circuit Board (PCB)
  • External voltage stabilizer

Related codes

Full explanation for 37
38

Your boiler started a flame but it went out immediately, so the system is trying to restart itself to get your heating back on.

High DIY-safe £100-£250

What to check first

  1. Check that your gas supply is active (e.g., check other gas appliances or credit on your meter)
  2. Press and hold the 'R' reset button for a few seconds to clear the fault
  3. Ensure the condensate pipe (plastic pipe leading outside) isn't frozen if it is winter

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve

Related codes

Full explanation for 38
Showing 21–30 of 54
43

Your boiler is struggling to keep its flame lit, which may be caused by strong winds affecting the flue or a technical issue with the burner.

High Engineer only £90-250

Parts commonly replaced

  • Ionisation probe
  • Spark electrode
  • Gas valve
  • Flue seals

Related codes

Full explanation for 43
45

Your boiler is overheating because the water is not flowing through the system quickly enough.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is between 1.0 and 1.5 bar on the gauge
  3. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation Pump
  • Main Heat Exchanger (flush required)
  • Flow or Return Sensor

Related codes

Full explanation for 45
47

Your boiler is overheating because the exhaust gases are too hot, so it is running at a lower power level to protect itself from damage.

Medium Engineer only £120-300

Parts commonly replaced

  • Flue Thermostat
  • Main Heat Exchanger (Cleaning or Replacement)
  • Burner Insulation

Related codes

Full explanation for 47
51

Your boiler has lost its wireless connection to the external temperature controller, meaning it may not know when to turn on or off.

Medium DIY-safe £0-180

What to check first

  1. Check the batteries in your wall-mounted thermostat or Climatic controller.
  2. Ensure the controller is within range of the boiler and there are no large metal objects blocking the signal.
  3. Try resetting the boiler and re-pairing the transmitter according to your manual.

Parts commonly replaced

  • Climatic controller batteries
  • RF Receiver unit
  • Wireless Transmitter
Full explanation for 51
60

Your boiler's internal pump has stopped circulating water, which means the system cannot heat your radiators or water to prevent itself from overheating.

High Engineer only £220-450

Parts commonly replaced

  • Circulating Pump
  • Pump head
  • Main PCB

Related codes

Full explanation for 60
61

Your boiler is struggling to push water around your radiators, likely because there is trapped air in the pipes or a blockage in the system.

High DIY-safe £90-250

What to check first

  1. Check that all radiator valves are fully open
  2. Carefully bleed all radiators to remove trapped air
  3. Ensure the boiler pressure gauge is between 1.0 and 1.5 bar
  4. Reset the boiler after checking valves and air

Parts commonly replaced

  • None - often resolved by a system flush
  • External heating filter
  • Circulation pump

Related codes

Full explanation for 61
70

Your boiler has detected that water is flowng incorrectly or sensors are giving conflicting readings, often due to a blockage in the system or a wiring issue.

High Engineer only £120-350

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring Harness
  • Main Heat Exchanger

Related codes

Full explanation for 70
75

Your boiler has detected an issue with its internal temperature sensors, meaning it cannot accurately monitor the water heat and has shut down as a precaution.

High Engineer only £120-190

Parts commonly replaced

  • NTC Temperature Sensor
  • Flow or Return Thermistor

Related codes

Full explanation for 75
76

Your boiler has detected a potential electronic fault with its internal temperature sensors, which means it cannot accurately monitor the water heat.

High Engineer only £120-£210

Parts commonly replaced

  • NTC Temperature Sensor
  • Flow/Return Thermistor
  • Wiring Harness

Related codes

Full explanation for 76
E01

Your boiler has tried to light several times but has failed, which means the system has locked itself out for safety.

High DIY-safe £100-350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas is reaching your home.
  2. Verify that your gas prepaid meter (if applicable) is in credit.
  3. Press and hold the 'R' Reset button for several seconds to try and restart the boiler.

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Lead
  • PCB

Related codes

Full explanation for E01
Showing 31–40 of 54
E02

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £100-280

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure there is enough pressure in the system by checking the gauge is between 1 and 1.5 bar.
  3. Wait for the boiler to cool down and try pressing the 'Reset' button.

Parts commonly replaced

  • Overheat Thermostat
  • Circulation Pump
  • Heat Exchanger (cleaning or replacement)

Related codes

Full explanation for E02
E03

Your boiler has detected that the exhaust gases are getting too hot, so it has shut down as a safety precaution to prevent internal damage.

High Engineer only £120-280

Parts commonly replaced

  • Flue thermostat
  • Main heat exchanger
  • Temperature sensor (NTC)

Related codes

Full explanation for E03
E05

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 shut down for safety.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Flow NTC Sensor
  • Sensor wiring harness

Related codes

Full explanation for E05
E06

Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning you may experience inconsistent or no hot water.

Medium Engineer only £90-160

Parts commonly replaced

  • Domestic Hot Water (DHW) NTC Sensor
  • Wiring harness

Related codes

Full explanation for E06
E08

Your boiler has been manually reset too many times in a short period and has now locked itself out as a safety precaution.

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 approximately 30 seconds.
  3. Turn the power back on to clear the temporary lockout and allow the boiler to restart.

Parts commonly replaced

  • No parts usually required
  • Ignition Electrode (if underlying fault exists)
  • PCB (if software error persists)

Related codes

Full explanation for E08
E10

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

High DIY-safe £0-160

What to check first

  1. Locate the filling loop (usually blue-handled levers or a pull-out tab) underneath the boiler
  2. Slowly open the valves until you hear water entering the system
  3. Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.5 bar

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for E10
E15

Your boiler has detected a problem reading the temperature of the water coming back into the unit, preventing it from heating correctly.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC temperature sensor
  • Wiring harness
  • Main PCB

Related codes

Full explanation for E15
E16

Your boiler has detected an issue with its internal fan, which means it cannot safely clear away waste gases and has shut down to protect you.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for E16
E20

Your boiler detects a flame when it shouldn't be there, which is often caused by a sensing error or a valve problem.

High Engineer only £120-350

Parts commonly replaced

  • Ionisation Probe
  • Gas Valve
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E20
E24

Your boiler’s control panel buttons have detected a fault or are stuck, preventing you from changing settings or resetting the unit.

High DIY-safe £120-280

What to check first

  1. Check if any control buttons are physically stuck or jammed in the pressed position.
  2. Gently wipe the control panel with a dry microfiber cloth to remove debris or moisture.
  3. Turn the power to the boiler off at the fused spur switch, wait 30 seconds, and turn it back on to reboot the panel.

Parts commonly replaced

  • Control Interface/User Interface PCB
  • Display Ribbon Cable

Related codes

Full explanation for E24
Showing 41–50 of 54
E31

Your boiler is no longer talking to your external thermostat or remote controller, meaning you might not be able to control your heating properly.

Medium DIY-safe £80-220

What to check first

  1. Check if the batteries in your room thermostat or remote control need replacing
  2. Ensure the remote control is within range of the boiler and has not been moved
  3. Try resetting the boiler by turning the selector switch to 'RESET' and back

Parts commonly replaced

  • Remote control batteries
  • RF Receiver unit
  • External thermostat/control
  • Communication wiring
Full explanation for E31
E35

Your boiler has detected a flame when there shouldn't be one, or the flame signal is staying on after the boiler should have switched off.

High Engineer only £120-350

Parts commonly replaced

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

Related codes

Full explanation for E35
E38

Your boiler has lost its flame while running and has shut down as a safety precaution.

High DIY-safe £100-£280

What to check first

  1. Check if other gas appliances (like a hob) are working to ensure gas is reaching the property
  2. Check that your gas meter has credit if you have a prepayment meter
  3. Press and hold the reset button for several seconds to restart the boiler

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for E38
E40

Your boiler has detected an issue with the electricity supply entering your home, meaning the power frequency is inconsistent and the system has shut down to protect its internal electronics.

High Engineer only £100-350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabiliser

Related codes

Full explanation for E40
E41

Your boiler is repeatedly losing its flame, causing it to shut down for safety purposes because it cannot maintain a steady burn.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve
  • PCB

Related codes

Full explanation for E41
E42

One of the buttons on your boiler's control panel has become jammed or is being pressed down continuously.

Low DIY-safe £0-120

What to check first

  1. Gently press and release each button on the front panel to see if one is stuck in the 'in' position.
  2. Wipe the control panel with a dry cloth to ensure no grit or debris is jamming the buttons.
  3. Restart the boiler by turning the power off and back on at the fused spur switch.

Parts commonly replaced

  • Control panel fascia
  • PCB (Printed Circuit Board)

Related codes

Full explanation for E42
E43

Your boiler is struggling to keep a flame lit and has locked itself out for safety after several failed attempts.

High DIY-safe £100-300

What to check first

  1. Check that your gas emergency control valve is in the 'on' position
  2. Ensure you have credit on your gas meter if you use a pre-payment system
  3. Check if other gas appliances, like a hob, are working to confirm your gas supply is active
  4. Press and hold the 'R' (Reset) button for a few seconds to restart the boiler

Parts commonly replaced

  • Ignition electrode
  • Flame sensing electrode
  • Gas valve
  • Condensate trap

Related codes

Full explanation for E43
E44

Your boiler has stopped working because the internal computer has lost communication with the gas valve, preventing the system from producing heat or hot water.

High Engineer only £160 - £350

Parts commonly replaced

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

Related codes

Full explanation for E44
E51

Your boiler's fan is not spinning at the correct speed or has stopped working, which means the boiler cannot safely clear waste gases and will not ignite.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for E51
E76

Your boiler has detected a problem with the internal pump, which is preventing water from circulating through your heating system.

High Engineer only £220-380

Parts commonly replaced

  • Modulating Pump
  • Pump Cable Harness
  • Main PCB

Related codes

Full explanation for E76
Showing 51–54 of 54
E80

Your boiler has detected an internal electrical problem with the component that controls the gas supply, meaning it cannot safely ignite.

High Engineer only £220-400

Parts commonly replaced

  • Gas Valve
  • Printed Circuit Board (PCB)
  • Wiring Harness

Related codes

Full explanation for E80
ERR>07

Your boiler is currently running a maintenance check to test the flue emissions and is not experiencing an actual fault.

Low DIY-safe

What to check first

  1. Wait approximately 15 minutes for the service mode to time out automatically
  2. Switch the selector dial or power button to the 'Off' position and then back to 'On'
  3. Ensure the selector dials are not stuck in a test position

Related codes

Full explanation for ERR>07
ERR>CM

Your boiler has lost communication with its external smart controller or thermostat, which has caused the heating system to switch itself off as a precaution.

High DIY-safe £60-140

What to check first

  1. Check if your thermostat or Climatic control screen has power or needs new batteries.
  2. Ensure the wiring between the thermostat base and the wall is secure if it has been recently moved.
  3. Try resetting the boiler by turning the selector switch to the 'R' position for five seconds.
  4. Check if any nearby wireless devices are causing interference with the receiver.

Parts commonly replaced

  • Climatic Remote Control unit
  • RF Receiver
  • Communication wiring
Full explanation for ERR>CM
Sr

Your boiler is simply reminding you that its annual service is now due to ensure it continues to run safely and efficiently.

Low Engineer only £80-120
Full explanation for Sr