Heatline Compact 24 Fault codes & diagnostics

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

Combi Natural Gas 24 kW 2010-2015 Discontinued

Replaced by: Heatline Capriz2

Download the Heatline Compact 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.
2 Emergency 30 High 1 Medium

All 33 documented codes

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Err

Your boiler's electronic display panel is failing to communicate with the internal system, which means the boiler cannot operate or respond to your commands.

High Engineer only £150-300

Parts commonly replaced

  • User interface/Display PCB
  • Wiring harness

Related codes

F00

Your boiler has lost the ability to measure the temperature of the water being sent to your radiators, so it has shut down as a precaution to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • NTC flow temperature sensor

Related codes

F01

Your boiler has stopped working because it is unable to accurately measure the temperature of the water returning to it from your radiators.

High Engineer only £120-200

Parts commonly replaced

  • Return NTC sensor

Related codes

F10

Your boiler has stopped working because it is unable to accurately read the temperature of the water inside the heating system.

High Engineer only £120-220

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

F11

Your boiler has lost the ability to measure the temperature of the water returning to it, so it has shut down to prevent potential overheating.

High Engineer only £120-180

Parts commonly replaced

  • Return NTC sensor
  • Wiring harness

Related codes

F20

Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage to its internal components.

High Engineer only £120-250

Parts commonly replaced

  • NTC thermistor sensor
  • Pump
  • Primary heat exchanger

Related codes

F22

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

High DIY-safe £80-150

What to check first

  1. Locate the filling loop (a silver flexible hose) underneath the boiler.
  2. Open the small valve or tap on the loop to allow mains water into the boiler.
  3. Monitor the pressure gauge on the front until it reaches 1.5 bar, then turn the valve firmly off.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

F23

Your boiler has detected that the water is not circulating properly, meaning it is getting hot in one area but not moving to the rest of your system fast enough.

High Engineer only £150-300

Parts commonly replaced

  • Central heating pump
  • Flow and return thermistors
  • System filter blockage

Related codes

F24

Your boiler is struggling to move water around the system fast enough, likely due to low water pressure or a blockage.

High DIY-safe £120-250

What to check first

  1. Check your boiler pressure gauge; if it is below 1 bar, use the filling loop to top it up to 1.5 bar
  2. Ensure all radiator valves are fully open
  3. Turn the boiler off and back on again to reset the temporary fault

Parts commonly replaced

  • Central heating pump
  • System filter
  • Pressure sensor

Related codes

F26

Your boiler has detected a problem with the internal part that controls the flow of gas, meaning it cannot safely start up to provide heat or hot water.

High Engineer only £180-300

Parts commonly replaced

  • Gas valve stepper motor
  • Gas valve assembly

Related codes

Showing 11–20 of 33
F27

Your boiler is failing to detect a flame, so it has purposefully shut down to prevent gas from building up inside the system.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

F28

Your boiler is trying to start but the flame is not catching, meaning it cannot provide you with heating or hot water.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

F29

Your boiler has stopped because the internal flame keeps going out while it is trying to heat your water or home.

High Engineer only £120-250

Parts commonly replaced

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

Related codes

F32

Your boiler is struggling to push air through its system properly, which has caused it to stop working to keep you safe.

High Engineer only £150-250

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi tube
F49

Your boiler has lost the communication signal between the main controller and the heating system, meaning it cannot receive instructions to provide heat or hot water.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • External thermostat/programmer

Related codes

F61

Your boiler is unable to safely control the flow of gas required to ignite the flame, so it has shut itself down to prevent a safety hazard.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • Printed circuit board (PCB)
  • Wiring harness

Related codes

F62

Your boiler has detected an issue with its internal gas supply system and has safely shut itself down to prevent any unsafe operation.

Emergency Engineer only £180-300

Parts commonly replaced

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

Related codes

F63

Your boiler's internal computer has encountered a critical memory error and can no longer safely control the heating system, requiring professional attention.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

F64

The boiler's internal computer is malfunctioning, meaning the system is unable to safely control your heating and hot water.

High Engineer only £250-450

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

F65

Your boiler has detected that its internal computer has become dangerously hot and has shut itself down to prevent fire or electrical damage.

High Engineer only £200-400

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal ventilation cooling fan

Related codes

Showing 21–30 of 33
F67

Your boiler has detected an issue with the flame detection system, meaning it cannot confirm that the burner is safely lit and will refuse to operate as a precaution.

High Engineer only £150-300

Parts commonly replaced

  • Main circuit board (PCB)
  • Flame rectification electrode
  • Wiring harness

Related codes

F68

Your boiler is struggling to keep a steady flame, causing it to shut down for safety reasons.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification electrode
  • Ignition lead
  • PCB

Related codes

F70

Your boiler's electronic control panel is not communicating correctly with the main internal computer, which prevents the system from starting up safely.

High Engineer only £150-300

Parts commonly replaced

  • User Interface PCB
  • Main Control Board

Related codes

F71

Your boiler has lost the ability to accurately measure the temperature of the water used for your radiators, causing it to shut down for safety reasons.

High Engineer only £120-200

Parts commonly replaced

  • NTC flow temperature sensor
  • Wiring harness

Related codes

F72

Your boiler has detected an unusual temperature gap between the outgoing and incoming water, indicating the system is struggling to circulate heat correctly.

High Engineer only £150-250

Parts commonly replaced

  • NTC Temperature Sensors
  • Central Heating Pump
  • Plate Heat Exchanger

Related codes

F73

Your boiler is struggling to accurately measure the water pressure inside the system, which is preventing it from safely starting up your heating.

High Engineer only £120-220

Parts commonly replaced

  • Pressure sensor
  • Wiring harness

Related codes

F74

Your boiler's sensor is struggling to read your heating system's pressure, which prevents the unit from starting the heating or hot water safely.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

F76

Your boiler has detected an internal issue with a safety device designed to shut the system down if it gets too hot, and it will no longer operate until this is inspected.

High Engineer only £120-220

Parts commonly replaced

  • Thermal fuse link
  • Overheat thermostat
  • Wiring harness
F77

Your boiler has detected an issue with the internal component that controls the gas supply, meaning it cannot safely ignite to provide heating or hot water.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

F83

Your boiler has lost its connection to the internal water pump, meaning it cannot circulate heat around your home.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • Wiring harness
  • Printed Circuit Board

Related codes

Showing 31–33 of 33
F84

Your boiler is confused because its temperature sensors are giving conflicting readings or are not properly connected, causing it to stop heating your home to prevent potential damage.

High Engineer only £120-200

Parts commonly replaced

  • NTC Temperature Sensor
  • Wiring harness

Related codes

F85

Your boiler's temperature sensors are reporting conflicting information because they are detecting heat from the same spot, causing the system to stop heating for safety.

High Engineer only £120-220

Parts commonly replaced

  • NTC temperature sensors
  • Wiring harness

Related codes

F86

Your boiler has lost the signal from the sensor that monitors your underfloor heating system, preventing it from activating those circuits.

Medium Engineer only £120-200

Parts commonly replaced

  • Underfloor heating sensor
  • Wiring harness
  • PCB

78 operating states & engineer diagnostics

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

d.00 Diagnostic This code is not actually an error; it simply displays the current power level the boiler is using to heat your home. d.01 Diagnostic Your boiler is currently running its pump for a short time after the heating has switched off to clear any remaining heat from the system, which is a normal part of the shutdown process. d.02 Diagnostic Your boiler is perfectly fine; it is simply pausing for a few minutes between heating cycles to prevent unnecessary wear and tear. d.08 Diagnostic Your boiler is simply reporting that it is currently receiving a signal from your wall thermostat to turn on the heating. d.09 Diagnostic Your boiler is receiving an instruction from an external smart controller or thermostat to set the water temperature, which is a normal part of its operation. d.10 Diagnostic Your boiler is struggling to circulate water properly, which means it cannot deliver heat to your radiators or taps. d.16 Diagnostic Your boiler is simply reporting that it is currently receiving a signal from your wall-mounted thermostat to either turn the heating on or off. d.17 Diagnostic Your boiler is struggling to accurately measure the temperature of the water circulating through your heating system, so it has stopped working to prevent potential damage. d.18 Diagnostic Your boiler is struggling to circulate water around your radiators and taps because the internal pump is not working as expected. d.20 Diagnostic Your boiler is currently monitoring or adjusting the temperature limit for your hot water supply, and this message indicates that the system is functioning within its set parameters. d.22 Diagnostic Your boiler is simply letting you know that it has detected you are running a hot water tap or shower and is currently working to heat that water. d.23 Diagnostic Your boiler is currently operating normally and is in the process of heating your radiators. d.33 Diagnostic Your boiler is struggling to get the internal air circulation fan spinning at the correct speed to operate safely. d.34 Diagnostic Your boiler is struggling to detect the speed of the fan that expels exhaust gases, so it has safely shut itself down to prevent unsafe operation. d.35 Diagnostic Your boiler is struggling to switch between providing hot water for your taps and heating your radiators because a internal valve is stuck or not responding correctly. d.36 Diagnostic Your boiler is struggling to detect or regulate the flow of water needed to provide hot water to your taps. d.40 Diagnostic Your boiler is measuring an unusually high or unexpected temperature in the water pipes, suggesting it is struggling to circulate heat correctly. d.41 Diagnostic Your boiler is struggling to accurately measure the temperature of the water returning from your radiators, which may cause it to turn off to prevent overheating. d.44 Diagnostic Your boiler is having difficulty detecting the flame, which means it cannot safely keep the burner lit to heat your water. d.67 Diagnostic Your boiler is currently in a brief, automatic resting period between heating cycles to protect its internal parts, and it will resume working shortly on its own. d.68 Diagnostic Your boiler is struggling to light the flame on the first try, but it is currently managing to work after subsequent attempts. d.69 Diagnostic Your boiler is failing to light the flame after two attempts, so it has shut down to prevent wasting gas. d.71 Diagnostic Your boiler has detected that the maximum temperature limit for your radiators has been set incorrectly or is being restricted by the system settings. d.80 Diagnostic This code is simply an information display showing how many hours your boiler has spent providing central heating, rather than indicating a fault. d.81 Diagnostic This code is simply an information display showing how many hours your boiler has spent heating your hot water, rather than a sign of a fault. d.82 Diagnostic This code is simply an information display showing how many times your boiler has started to provide heating, and it does not indicate a fault or a problem with your system. d.83 Diagnostic This code is simply an information display showing how many times your boiler has started to heat your hot water, rather than indicating a fault. d.85 Diagnostic Your boiler is currently running at its lowest possible power setting for your heating system, which may result in radiators not getting as warm as usual. d.93 Diagnostic Your boiler's electronic brain is displaying its unique identification code, which is an internal factory setting rather than a functional breakdown. d.94 Diagnostic Your boiler is signalling that a system reset is required to clear its internal memory and try to restart normally. d.96 Diagnostic Your boiler has reverted to its original factory settings, which means any previous custom adjustments have been wiped and it may need to be reconfigured to work with your specific home setup. P.01 Diagnostic Your boiler is currently locked in a manual testing mode that forces it to run at maximum power, which is not a normal operating state for heating your home. P.02 Diagnostic Your boiler is currently running a self-diagnostic test to ensure it can safely ignite, which is a normal part of its internal operating process. P.03 Diagnostic Your boiler is currently running at its maximum power setting for a diagnostic test or internal process, rather than a standard operational fault. P.05 Diagnostic Your boiler is currently refilling its internal water system to ensure it has enough pressure to operate correctly. P.06 Diagnostic Your boiler is currently running an automated program to remove trapped air from the internal system to ensure efficient water circulation. P.07 Diagnostic Your boiler is currently running a brief automated cycle to clear trapped air from the water pump to ensure it can circulate heat correctly. S.00 Status Your boiler is currently in standby mode because it has not received a signal from your thermostat to turn on the heating. S.01 Status Your boiler is currently performing a required safety check by running its internal fan before attempting to light the flame. S.02 Status Your boiler is currently performing a routine internal check to ensure water is circulating properly before it attempts to fire up the burner. S.03 Status Your boiler is failing to light the flame needed to produce heat or hot water. S.04 Status Your boiler is operating normally and the burner has successfully ignited to provide heat or hot water. S.05 Status Your boiler is currently cooling down by running its internal components to clear heat, which is a normal part of the shutdown process. S.06 Status Your boiler is currently running its internal fan to safely vent any remaining gases after the burner has turned off, which is a normal part of the shutdown process. S.07 Status Your boiler is simply performing a routine safety cycle where the pump continues to run for a short time after heating to distribute residual warmth. S.08 Status Your boiler is currently taking a temporary rest pause between heating cycles to prevent excessive wear and tear, which is a normal part of its operation. S.10 Status Your boiler is simply working as intended and is currently heating up water for your taps or shower. S.11 Status Your boiler is currently preparing to ignite, but the internal fan is checking its position before the system starts burning fuel. S.13 Status Your boiler is failing to light the flame, so it has safely stopped operating to prevent gas from building up inside. S.14 Status Your boiler is operating normally—this code simply indicates that the burner is currently lit and heating your water. S.15 Status Your boiler is currently performing a standard cool-down process after your heating or hot water has been running. S.16 Status Your boiler is simply performing a routine safety process where the fan runs for a short time after the heating switches off to clear any leftover gases safely. S.17 Status Your boiler is simply performing a routine safety cycle to circulate leftover heat away from the system, and no action is required. S.20 Status Your boiler is currently preparing to fire by checking the water circulation, which is a normal part of the start-up process. S.21 Status Your boiler is currently checking that its internal air extraction system is working correctly before it attempts to ignite the flame. S.23 Status Your boiler is failing to light the flame properly, meaning it cannot provide you with heating or hot water. S.24 Status Your boiler is operating normally and the burner is currently lit to provide heat or hot water. S.25 Status Your boiler is currently cooling down its internal components after finishing a heating or hot water cycle, which is a normal part of the shutdown process. S.26 Status Your boiler is simply finishing its cooling cycle after being in use, which is a normal part of its operation. S.27 Status Your boiler is simply finishing a final water circulation cycle to safely cool itself down after heating has been running. S.28 Status Your boiler has temporarily stopped heating your hot water cylinder because it has reached a protective safety limit meant to prevent the system from overheating. S.30 Status Your boiler is currently in standby mode because it hasn't received a signal from your thermostat or hot water tap to start heating. S.31 Status Your boiler is currently set to only provide hot water and is ignoring requests for central heating. S.32 Status Your boiler is struggling to operate its internal fan correctly, which is preventing it from safely lighting and heating your home. S.34 Status Your boiler has detected very low temperatures and is automatically firing up to protect its internal pipework from freezing. S.35 Status Your boiler is having trouble managing the airflow needed to operate safely and has shut down to prevent any issues. S.36 Status Your boiler has detected that water is not circulating properly through the heating system, which is preventing it from distributing warmth to your radiators. S.37 Status Your boiler has detected that the internal fan responsible for safely venting fumes is not spinning at the correct speed to run efficiently. S.41 Status Your boiler's internal water pressure is currently too high, which prevents it from operating safely to protect the system. S.53 Status Your boiler has paused its heating process because the water circulating through your radiators is not returning to the unit quickly enough, often due to a blockage or restricted flow. S.54 Status Your boiler has temporarily stopped heating because the water is not flowing through the system correctly, likely due to low water pressure or an airlock. S.58 Status Your boiler is temporarily running at a restricted, pre-set power level to protect itself, rather than adjusting its heat output normally. S.90 Status Your boiler is currently performing a mandatory internal self-check sequence and is not indicating a fault. S.92 Status Your boiler has detected that water is not flowing through the system correctly, which is preventing it from heating your home or your water. S.95 Status Your boiler has detected an electrical power problem that is preventing it from safely heating your home or water. S.96 Status Your boiler has detected that hot water cannot circulate properly through the system, so it has safely shut down to prevent overheating. S.97 Status Your boiler has detected that the water pressure sensor is not providing a signal, which prevents the heating and hot water from turning on. S.98 Status Your boiler has detected that hot water cannot flow through the pipes properly, which has caused it to stop working for your radiators and taps.