Alpha Intec 50CS Fault codes & diagnostics

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

Combi Natural Gas 50 kW 2012-present
GC Numbers 47-532-6647-532-6747-532-68
Download the Alpha Intec 50CS manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
6 Emergency 45 High 6 Medium 2 Low
Just want the most common Alpha Intec 50CS faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 59 documented codes

Tap any card for details

01

Your boiler is trying to start but is unable to light the flame needed to produce heat or hot water.

High DIY-safe £150-300

What to check first

  1. Press and hold the reset button for several seconds to restart the ignition sequence
  2. Check that your gas meter has credit and the isolation valve is open
  3. Test another gas appliance, like a hob, to ensure gas is being supplied to the property

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for 01
02

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent any damage or safety risks.

High DIY-safe £120-250

What to check first

  1. Check that your radiator valves are open
  2. Check that your boiler pressure is between 1.0 and 1.5 bar
  3. Press the 'Reset' button on the front control panel
  4. Ensure no air is trapped in the system by bleeding your radiators

Parts commonly replaced

  • High Limit Thermostat
  • Primary Heat Exchanger
  • Circulating Pump

Related codes

Full explanation for 02
03

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

High Engineer only £150-350

Parts commonly replaced

  • Flue thermostat
  • Primary heat exchanger
  • Pump

Related codes

Full explanation for 03
04

Your boiler has detected a faulty connection to the component that controls the gas supply, meaning it cannot safely turn on.

Emergency Engineer only £120-250

Parts commonly replaced

  • Gas valve wiring harness
  • Gas valve assembly
  • Main PCB

Related codes

Full explanation for 04
05

Your boiler is struggling to detect the temperature of the water flowing through your heating system, so it has turned itself off as a precaution.

High Engineer only £120-220

Parts commonly replaced

  • NTC Flow Sensor
  • Wiring harness

Related codes

Full explanation for 05
06

Your boiler is having trouble accurately measuring the temperature of the water used for your taps and shower.

High Engineer only £120-200

Parts commonly replaced

  • DHW NTC thermistor sensor

Related codes

Full explanation for 06
08

Your boiler has reached its safety limit for automatic restarts after repeated failures, meaning it has locked itself out to prevent further issues.

High Engineer only £120-250

Parts commonly replaced

  • Ignition lead
  • Ignition electrode
  • Gas valve

Related codes

Full explanation for 08
10

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

High DIY-safe £0-£120

What to check first

  1. Locate the external filling loop, usually two silver flexible hoses with small taps attached under the boiler.
  2. Open the taps slowly to allow water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.
  3. Close both taps tightly and check the boiler display to see if the fault has cleared.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

Full explanation for 10
12

Your boiler has detected that its internal settings do not match the way it has been physically plumbed into your home's heating system.

Medium Engineer only £120-250

Parts commonly replaced

  • PCB

Related codes

Full explanation for 12
15

Your boiler's computer is confused because its internal settings do not match the signals it is receiving, preventing it from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for 15
Showing 11–20 of 59
16

Your boiler has stopped working because it cannot properly clear exhaust gases, which is a safety mechanism to prevent harmful fumes from building up.

High Engineer only £180-300

Parts commonly replaced

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

Related codes

Full explanation for 16
20

Your boiler is confused because it thinks a flame is burning when it shouldn't be, or it cannot confirm the flame is lighting correctly, causing it to shut down for safety.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

Full explanation for 20
23

Your boiler has detected a communication error with a temperature sensor, which is preventing it from heating your home safely.

High Engineer only £120-220

Parts commonly replaced

  • Central Heating Return Thermistor

Related codes

Full explanation for 23
24

The boiler's control panel detects that one of the buttons is jammed, preventing it from functioning correctly.

High DIY-safe £100-200

What to check first

  1. Switch off the boiler at the electrical fused spur
  2. Gently press and release each button on the control panel to see if any feel stuck or fail to 'click'
  3. Use a dry, soft cloth or gentle air duster to remove any debris or sticky residue around the buttons
  4. Wait 5 minutes and switch the power back on to see if the error clears

Parts commonly replaced

  • Control panel/PCB interface
  • Fascia buttons

Related codes

Full explanation for 24
25

Your boiler has detected an abnormally fast rise in temperature and has shut itself down to prevent internal damage.

High Engineer only £150-350

Parts commonly replaced

  • NTC sensor
  • Primary heat exchanger
  • Pump

Related codes

Full explanation for 25
27

Your boiler is struggling to pump water around your heating system fast enough, causing it to overheat and shut down for safety.

High DIY-safe £150-300

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and isolation valves are fully open
  3. Bleed your radiators to remove any trapped air pockets

Parts commonly replaced

  • Central heating pump
  • Primary flow sensor
  • System bypass valve
  • Heat exchanger

Related codes

Full explanation for 27
29

Your boiler has detected that the sensor monitoring the temperature of the gases leaving the flue is reading incorrectly, so it has safely shut down to prevent potential overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flue temperature sensor
  • Wiring harness

Related codes

Full explanation for 29
31

Your boiler has lost its connection to its smart thermostat, meaning it cannot receive instructions on when to turn the heating or hot water on.

Medium DIY-safe £90-180

What to check first

  1. Check if the batteries in your Alpha Climatic control unit are dead and replace them if necessary
  2. Ensure the control unit is correctly docked or within range of the boiler
  3. Turn the boiler off at the fused spur for 60 seconds and then switch it back on to reset the connection

Parts commonly replaced

  • Alpha Climatic control unit
  • Wireless receiver module

Related codes

Full explanation for 31
32

Your boiler is having trouble communicating with the temperature sensor for your secondary heating area, which may cause that part of your home to not heat up correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • NTC Sensor
  • Wiring harness

Related codes

Full explanation for 32
34

Your boiler has detected that a secondary heating circuit, such as underfloor heating, has become too hot and has automatically shut down to prevent damage.

Medium Engineer only £120-250

Parts commonly replaced

  • Safety thermostat
  • Mixing valve
  • Circulation pump

Related codes

Full explanation for 34
Showing 21–30 of 59
35

Your boiler has detected that a specific part of your heating system has reached a dangerously high temperature and has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Safety thermostat
  • Zone pump
  • Overheat sensor

Related codes

Full explanation for 35
36

Your boiler is displaying a communication error that shouldn't exist on this specific model, suggesting a temporary glitch in its internal computer system.

Low DIY-safe £0-100

What to check first

  1. Switch the boiler off at the power supply for 30 seconds
  2. Turn the power back on to allow the boiler to perform a full system reset
  3. Check if the error code clears from the display

Parts commonly replaced

  • Main printed circuit board (PCB)

Related codes

Full explanation for 36
37

Your boiler is struggling because it is not receiving enough electricity from your home's power supply to run safely.

High Engineer only £120-250

Parts commonly replaced

  • Main printed circuit board (PCB)
  • Wiring harness
  • Fused spur switch

Related codes

Full explanation for 37
38

Your boiler is struggling to keep the flame alight once it has started, so it is automatically pausing to try again safely.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

Full explanation for 38
43

Your boiler is struggling to stay lit because the flame keeps going out, which can sometimes happen during very windy weather.

High DIY-safe £150-250

What to check first

  1. Check if there are currently gale-force winds outside affecting your flue pipe
  2. Wait for the wind to die down and press the reset button
  3. Ensure the external flue terminal is not blocked by debris or garden foliage

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Gas valve

Related codes

Full explanation for 43
44

Your boiler has failed to light after several attempts and has switched itself off for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 44
45

Your boiler has detected that the water leaving your heating system is returning much cooler than expected, suggesting a blockage or a failure to circulate heat properly.

High DIY-safe £150-350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure your system pressure is between 1.0 and 1.5 bar
  3. Check for any strange noises that might suggest a pump blockage

Parts commonly replaced

  • Central heating pump
  • Plate-to-plate heat exchanger
  • System filter

Related codes

Full explanation for 45
46

Your boiler has detected an interruption in a safety circuit, likely caused by an external add-on like a frost protection sensor or safety thermostat being triggered or disconnected.

High Engineer only £120-250

Parts commonly replaced

  • External frost thermostat
  • Wiring loom link
  • Safety circuit thermal fuse

Related codes

Full explanation for 46
47

Your boiler has detected that the exhaust gases are getting too hot, so it is slowing down its performance to avoid damaging itself and to prevent a total shutdown.

High Engineer only £150-300

Parts commonly replaced

  • Primary heat exchanger
  • Flue thermostat
  • NTC sensor

Related codes

Full explanation for 47
51

Your boiler has lost its wireless connection to your room thermostat or controller, meaning it doesn't know when to turn your heating on or off.

Medium DIY-safe £100-200

What to check first

  1. Check the batteries in your room thermostat and replace them with fresh ones.
  2. Turn the boiler off at the fused spur for 60 seconds to reset the receiver, then turn it back on.
  3. Attempt to re-pair the thermostat to the receiver following the instructions in your user manual.

Parts commonly replaced

  • Wireless receiver module
  • RF control thermostat
  • PCB circuit board
Full explanation for 51
Showing 31–40 of 59
59

Your boiler is struggling to read the electricity coming from your home's power supply, preventing it from starting up safely.

High Engineer only £150-300

Parts commonly replaced

  • Main PCB

Related codes

Full explanation for 59
60

Your boiler has detected that the water pump responsible for circulating heat around your home is jammed or experiencing an electrical issue, meaning it cannot provide you with heating or hot water.

High Engineer only £200-350

Parts commonly replaced

  • Central heating pump
  • Pump head
  • Circulation pump wiring harness

Related codes

Full explanation for 60
61

Your boiler is struggling because air bubbles are trapped inside the system, preventing the water from circulating properly to heat your home.

Medium DIY-safe £90-180

What to check first

  1. Check your boiler pressure gauge and ensure it is between 1.0 and 1.5 bar
  2. Bleed all radiators in your home starting from the lowest floor to the highest
  3. Top up the system pressure again to 1.5 bar if it dropped while bleeding
  4. Restart the boiler to see if the error clears

Parts commonly replaced

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

Related codes

Full explanation for 61
73

Your boiler has detected conflicting temperature readings between its internal sensors, leading it to shut down for safety reasons.

High Engineer only £150-250

Parts commonly replaced

  • Flow NTC sensor
  • Safety NTC sensor
  • Wiring harness

Related codes

Full explanation for 73
74

Your boiler has detected a faulty reading from an internal temperature sensor, causing it to shut down for safety reasons.

High Engineer only £150-250

Parts commonly replaced

  • NTC Sensor
  • Wiring harness
  • PCB

Related codes

Full explanation for 74
77

Your boiler has detected an issue with the internal component that controls the flow of gas, which is preventing it from lighting safely.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

Full explanation for 77
78

Your boiler has detected an issue with the internal component that controls the gas supply, meaning it has safely shut itself down to prevent unsafe operation.

Emergency Engineer only £150-350

Parts commonly replaced

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

Related codes

Full explanation for 78
79

Your boiler has detected an internal error with the mechanism that controls the fuel supply, meaning it has safely shut itself down to prevent unsafe operation.

Emergency Engineer only £150-£300

Parts commonly replaced

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

Related codes

Full explanation for 79
80

Your boiler has detected an internal electrical problem that is preventing it from safely opening the gas supply, so it has shut down to protect your home.

High Engineer only £250-450

Parts commonly replaced

  • Main Control PCB
  • Gas Valve

Related codes

Full explanation for 80
84

Your boiler is not receiving enough gas to run at full power, so it has automatically limited its own performance to keep you safe.

High Engineer only £120-250

Parts commonly replaced

  • Gas valve
  • Gas meter regulator

Related codes

Full explanation for 84
Showing 41–50 of 59
87

Your boiler has detected an internal safety fault in the part that manages the gas supply, meaning it has shut down to prevent unsafe operation.

High Engineer only £250-450

Parts commonly replaced

  • Gas valve
  • Main PCB
Full explanation for 87
88

Your boiler has detected an internal issue with the part that manages the gas supply, so it has safely shut itself down to prevent any risk.

Emergency Engineer only £150-350

Parts commonly replaced

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

Related codes

Full explanation for 88
89

Your boiler is struggling to keep its internal flame lit steadily, so it has safely shut itself down to prevent any issues.

High Engineer only £150-300

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Venturi or fan assembly

Related codes

Full explanation for 89
90

Your boiler has detected an abnormal reading from the flame sensor, meaning it cannot safely determine if the burner is operating correctly and has shut down as a precaution.

High Engineer only £120-250

Parts commonly replaced

  • Flame ionization electrode
  • PCB

Related codes

Full explanation for 90
91

Your boiler is trying to start but failing to keep the flame lit, which means it has automatically shut down to stay safe.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for 91
92

Your boiler's fan is struggling to push air out as it should, meaning the unit has stopped working to keep you safe.

High Engineer only £150-350

Parts commonly replaced

  • Fan assembly
  • Flue system assembly
  • PCB

Related codes

Full explanation for 92
93

Your boiler has detected an issue with the flame sensor reading, meaning it cannot safely regulate the internal flame and has shut down to prevent damage.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

Full explanation for 93
94

Your boiler has detected a problem with burning fuel safely and has shut itself down to prevent any potential danger.

Emergency Engineer only £150-300

Parts commonly replaced

  • Flue seal
  • Gas valve
  • Burner assembly
  • Air pressure switch

Related codes

Full explanation for 94
95

Your boiler is struggling to keep a steady flame, causing it to shut down because it cannot safely maintain the fire needed to heat your home.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensor lead

Related codes

Full explanation for 95
96

Your boiler has detected a blockage in the ventilation system, meaning it cannot exhaust fumes safely and has shut down to prevent a hazard.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue fan
  • Air pressure switch
  • Flue seal

Related codes

Full explanation for 96
Showing 51–59 of 59
98

Your boiler's computer has encountered too many internal processing errors and has locked itself down as a safety precaution.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 98
99

Your boiler has detected a general internal fault that has caused it to stop working for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Main printed circuit board
  • Wiring harness
  • Gas valve

Related codes

Full explanation for 99
CE

Your boiler is receiving an unusual reading from an external weather-sensing device linked to your heating system, signaling that the correction value is set incorrectly.

Low Engineer only £90-180

Parts commonly replaced

  • External sensor
  • Outdoor probe

Related codes

Full explanation for CE
E03

Your boiler has detected that the internal exhaust area is getting too hot and has automatically shut down for your safety.

High Engineer only £150-300

Parts commonly replaced

  • Flue thermostat
  • High limit sensor
  • NTC thermistor
  • Fan

Related codes

Full explanation for E03
E38

Your boiler has stopped working because it cannot maintain a stable flame, meaning it is currently unable to provide you with heating or hot water.

High DIY-safe £150-350

What to check first

  1. Check if other gas appliances, like a hob, are working to ensure gas supply is active
  2. Check if your gas meter has credit
  3. Press and hold the reset button for several seconds

Parts commonly replaced

  • Ignition electrode
  • Flame rectification probe
  • Gas valve
  • PCB

Related codes

Full explanation for E38
E62

Your boiler has lost its internal settings regarding the type of fuel it uses and requires a professional engineer to perform a re-calibration to function safely.

High Engineer only £100-£200

Parts commonly replaced

  • None - requires electronic recalibration
Full explanation for E62
E72

Your boiler has lost its fine-tuned settings and needs to recalibrate its internal systems to function correctly again.

High DIY-safe £120-180

What to check first

  1. Locate the selector switch on the front of the boiler
  2. Turn the selector to the 'RESET' position for approximately 5 seconds
  3. Return the selector to the 'ON' position and wait for the boiler to complete its automatic calibration cycle

Parts commonly replaced

  • Main PCB
  • Gas Valve
Full explanation for E72
Fixed red LED

Your boiler has stopped circulating water because a critical internal component is stuck, meaning you currently have no heating or hot water.

High DIY-safe £150-300

What to check first

  1. Turn the boiler power off and then back on to see if the pump restarts
  2. Locate the selector switch and turn it to the 'Reset' position for 5 seconds, then back to 'On'
  3. Check that your radiator valves are open to ensure water can flow

Parts commonly replaced

  • Circulation pump
  • Pump capacitor

Related codes

Full explanation for Fixed red LED
STOP

Your boiler has blocked itself from restarting due to too many failed attempts and needs to remain off for an hour before it will let you try again.

High DIY-safe £120-250

What to check first

  1. Switch off the power to the boiler at the fused spur switch.
  2. Wait for at least 60 minutes without pressing any buttons.
  3. Turn the power back on and see if the error has cleared to allow one further reset attempt.

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

Full explanation for STOP
Status & diagnostic codes

3 operating states & engineer diagnostics

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

62 Diagnostic Your boiler has lost its specific operating settings and needs a professional engineer to electronically recalibrate it to ensure it is burning fuel safely and efficiently. 72 Diagnostic Your boiler's computer system has detected that some of its internal settings have drifted or been changed, and it needs a professional to recalibrate it to run correctly. F4 Status Your boiler is simply performing a routine safety clear-out to remove any remaining exhaust gases after finishing a heating or hot water cycle.
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