Navien NCB 35 HE Fault codes & diagnostics

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

Combi Natural GasLPG 35 kW 2015-present

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12 Emergency 83 High 8 Medium 5 Low

All 108 documented codes

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001

Your boiler has detected an internal communication error and has safely shut itself down as a precaution.

High Engineer only £150-250

Parts commonly replaced

  • Main PCB
  • Communication wiring harness

Related codes

003

Your boiler has failed to light the flame properly and has stopped attempting to heat your home or water for safety reasons.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensor

Related codes

004

Your boiler has detected a false flame signal, meaning the system thinks the burner is lit when it should be turned off.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification probe
  • Gas valve
  • Main PCB

Related codes

004E

Your boiler has detected a flame signal when it shouldn't have, but it is currently attempting to clear this error automatically.

Medium Engineer only £120-250

Parts commonly replaced

  • Flame sensor
  • Ignition electrode
  • PCB

Related codes

5.2.15 Error 517

Your boiler has detected that its internal configuration settings have not been set correctly, causing it to stop operating.

High Engineer only £120-200

Parts commonly replaced

  • Main PCB

Related codes

5.2.19 Error 782

Your boiler's main internal controller has lost its connection, meaning it cannot receive signals from the display panel to operate your heating and hot water.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Communication cable

Related codes

012

Your boiler has detected that it is not receiving enough water flow to operate safely or effectively.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Pump
  • Diverter valve

Related codes

016

Your boiler has detected an issue related to the flow of water inside the unit, which has caused it to stop working to protect itself from potential overheating.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Circulation pump
  • Diverter valve
030

Your boiler has failed to ignite or has lost the flame during operation because it is not receiving a consistent supply of gas.

High Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Flame detection sensor

Related codes

031

Your boiler has detected an issue with the air supply or exhaust ventilation that prevents it from firing up safely.

High Engineer only £120-250

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Flue seals

Related codes

Showing 11–20 of 108
046

Your boiler has detected an issue with the sensors that monitor the water flow, which is preventing it from firing up correctly.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Wiring harness
  • PCB

Related codes

047

Your boiler has detected a problem with the internal fan that controls the airflow needed to operate safely.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • PCB
  • Wiring harness
060

Your boiler has detected an issue with the air supply or exhaust system, meaning it cannot operate safely and has shut down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Flue system components
109

Your boiler has detected an issue with the airflow or exhaust system, meaning it cannot operate safely and has shut itself down.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Air pressure sensor
  • Flue assembly

Related codes

110

Your boiler has detected that it is not effectively removing waste gases produced during the heating process, causing it to shut down for safety.

Emergency Engineer only £150-350

Parts commonly replaced

  • Flue system components
  • Air pressure switch
  • Fan assembly

Related codes

110E

Your boiler is struggling to breathe properly because the pipework that lets out waste gases or takes in fresh air is blocked or damaged.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue kit
  • Condensate trap
  • Fan assembly
  • Air pressure switch

Related codes

205

Your boiler has detected an issue with the air flowing through the flue system, causing it to shut down for safety.

High Engineer only £150-300

Parts commonly replaced

  • Fan assembly
  • Air pressure switch
  • Flue seals
218

Your boiler has detected an issue with the water pressure sensor, preventing it from knowing if there is enough water to safely heat your home.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
302

Your boiler has detected an issue with the air flowing through the system, preventing it from starting safely.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Flue fan
  • Venturi
352

Your boiler is experiencing a communication failure between the control panel and the main operating system preventing it from firing up correctly.

High Engineer only £150-300

Parts commonly replaced

  • Main PCB
  • Wiring Harness
  • Control Display Unit

Related codes

Showing 21–30 of 108
353

Your boiler has detected an issue with the air supply or exhaust ventilation system that prevents it from firing safely.

High Engineer only £150-300

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Flue ducting

Related codes

407

Your boiler has detected an issue with the sensor that tracks the flow of water, which is preventing the system from operating correctly.

High Engineer only £150-250

Parts commonly replaced

  • Flow sensor
  • Water flow switch
421

Your boiler has detected a problem with the water flow or pressure sensors that prevents it from firing up reliably.

High Engineer only £150-300

Parts commonly replaced

  • Flow sensor
  • Water pressure sensor
  • Main PCB
515

Your boiler has detected an internal communication error between its main computer and the internal control systems, which prevents it from operating safely.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Wiring harness
517

Your boiler has detected an internal communication error between its main computer and the internal control system, causing it to stop working for safety reasons.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Wiring harness
594

Your boiler has detected an internal communication problem with the air pressure sensor, which is preventing it from safely starting up.

High Engineer only £180-350

Parts commonly replaced

  • Air pressure sensor
  • PCB (Main control board)
  • Wire harness
615

Your boiler's fan is failing to run correctly, which prevents it from safely venting gases, so the system has shut down to protect your home.

High Engineer only £180-350

Parts commonly replaced

  • Exhaust fan assembly
  • Fan wiring harness
  • PCB (Main control board)
740

Your boiler's external temperature sensor is reporting an issue, which may cause it to run inefficiently or struggle to heat your home correctly.

Medium Engineer only £120-200

Parts commonly replaced

  • External temperature sensor
  • Wiring harness
760

Your boiler has reached its programmed service timer and is simply reminding you that it is time to have a professional technician perform a routine maintenance check to prevent limescale buildup.

Low Engineer only £100-180

Parts commonly replaced

  • Service kit/seals
762

Your boiler has detected that the flue pipe responsible for safely venting exhaust gases outside has become loose or disconnected.

Emergency Engineer only £120-250

Parts commonly replaced

  • Flue assembly seals
  • Vent installation detector switch
  • Flue pipe sections
Showing 31–40 of 108
782

Your boiler has detected an internal communication or software management error that requires a professional to reset or update its internal settings.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
  • Communication wiring harness
E.782

Your boiler's main control unit and the display panel are having trouble 'talking' to each other, which prevents the system from operating correctly.

High Engineer only £150-300

Parts commonly replaced

  • Main control board
  • Communication interface cable
  • Display panel assembly
E01

Your boiler has failed to light the flame properly, meaning it cannot produce heat or hot water.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensor

Related codes

E001

Your boiler has detected that the water temperature inside is getting dangerously high and has shut itself down to prevent damage or overheating.

High Engineer only £150-350

Parts commonly replaced

  • Primary heat exchanger
  • Flow sensor
  • Circulation pump
  • NTC thermistor

Related codes

E02

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate the filling loop (usually two silver flexible hoses) underneath the boiler.
  2. Open the valves slowly to allow mains cold water into the system.
  3. Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.0 to 1.5 bar).
  4. Close both valves tightly to stop the flow of water.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel

Related codes

E002

Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.

High DIY-safe £80-120

What to check first

  1. Locate the external filling loop, usually found underneath the boiler.
  2. Gradually open the filling loop valves to allow water into the system while watching the pressure gauge.
  3. Stop filling once the needle reaches the green zone, typically between 1.0 and 1.5 bar.
  4. Ensure both valves are fully closed and tight.

Parts commonly replaced

  • Pressure Transducer
  • Filling Loop
  • Expansion Vessel

Related codes

E003

Your boiler has failed to light the flame needed to heat your water and home.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensor

Related codes

E03

Your boiler has detected that parts inside are getting too hot and has automatically shut down to prevent damage.

High Engineer only £150-350

Parts commonly replaced

  • Heat Exchanger
  • Pump
  • Diverter Valve

Related codes

E004

Your boiler has detected a flame when it shouldn't be burning, suggesting a sensor error or a gas valve issue that prevents the unit from starting safely.

High Engineer only £150-300

Parts commonly replaced

  • Flame rectification probe
  • Gas valve
  • Main PCB

Related codes

E04

Your boiler has detected that the gases leaving the unit are getting too hot, so it has safely shut down to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • Exhaust gas temperature sensor
  • Heat exchanger
  • Fan assembly

Related codes

Showing 41–50 of 108
E005

Your boiler has stopped because the internal flame has unexpectedly gone out while it was running.

High Engineer only £150-300

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Gas valve

Related codes

E05

Your boiler has detected an issue with its internal air extraction system, which means it cannot safely clear emissions and has shut down to prevent any risk.

High Engineer only £150-350

Parts commonly replaced

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

Related codes

E012

Your boiler is failing to stay lit, so it has shut down to keep you safe.

High Engineer only £120-£250

Parts commonly replaced

  • Ignition electrode
  • Flame sensor
  • Gas valve
E12

Your boiler has detected a potential issue with the gas supply or the internal gas valve, and to keep you safe, it has automatically locked itself to prevent operation.

Emergency Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • Gas pressure switch
  • Main PCB

Related codes

E13

Your boiler is struggling to detect the movement of water, which means it will prevent your hot water or heating from starting to protect the system from overheating.

High Engineer only £150-250

Parts commonly replaced

  • Flow switch sensor
  • Wiring harness

Related codes

E15

Your boiler's main control computer is experiencing a communication or processing error, which has caused it to stop working for safety reasons.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

E016

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

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • Flow sensor
  • Heat exchanger
  • Diverter valve

Related codes

E16

Your boiler has detected that parts inside are getting dangerously hot and has shut itself down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Overheat sensor
  • Heat exchanger
  • Pump

Related codes

E18

Your boiler has detected that the temperature of the gases leaving the flue is higher than it should be, so it has safely shut itself down to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • Exhaust gas temperature sensor
  • Heat exchanger
  • Flue assembly

Related codes

E27

Your boiler is struggling to clear exhaust gases safely, so it has stopped working to prevent any risk.

High Engineer only £180-350

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Flue seals

Related codes

Showing 51–60 of 108
E030

Your boiler has detected that the gases leaving the unit are hotter than they should be, causing it to shut down to prevent overheating.

Emergency Engineer only £150-350

Parts commonly replaced

  • Exhaust temperature sensor
  • Heat exchanger
  • Fan assembly

Related codes

E30

Your boiler has detected that the sensor monitoring the heat of the exhaust gases is not reading correctly, which prevents it from operating safely.

High Engineer only £150-250

Parts commonly replaced

  • Exhaust gas temperature sensor
  • Wiring harness
  • PCB

Related codes

E031

Your boiler has detected that it is running much hotter than it should be and has switched itself off to prevent damage.

Emergency Engineer only £150-350

Parts commonly replaced

  • High limit thermostat
  • Heat exchanger
  • Circulation pump
  • PCB
E31

Your boiler is failing to ignite because it cannot regulate the gas supply correctly, which means you currently have no heating or hot water.

Emergency Engineer only £180-350

Parts commonly replaced

  • Gas valve
  • PCB (Main control board)
  • Wiring harness

Related codes

E046

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

High Engineer only £120-250

Parts commonly replaced

  • Main Heat Exchanger
  • Pump
  • Diverter Valve

Related codes

E46

Your boiler is struggling to detect the outside temperature, so it is defaulting to a basic heat setting to keep your home warm while ignoring external weather conditions.

Low Engineer only £120-200

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring loom
E047

Your boiler has detected that the temperature in the exhaust flue is too high, causing it to shut down for safety reasons.

Emergency Engineer only £150-300

Parts commonly replaced

  • Exhaust temperature sensor
  • Flue duct assembly
  • Primary heat exchanger
E47

Your boiler is struggling to accurately measure how much water is inside the system, which is preventing it from firing up safely.

High Engineer only £120-200

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

E51

Your boiler’s internal computer is confused because its physical configuration switches are set incorrectly, preventing it from starting safely.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
E060

Your boiler is having trouble managing the air and gas mixture needed to burn fuel safely and effectively.

High Engineer only £150-300

Parts commonly replaced

  • Venturi unit
  • Gas valve
  • Air pressure switch
Showing 61–70 of 108
E60

Your boiler's electronic display and its internal computer are failing to communicate with each other, meaning the unit cannot receive instructions or show system status.

High Engineer only £150-300

Parts commonly replaced

  • Control panel/display unit
  • Communication cable
  • Main PCB
E109

Your boiler's fan is struggling to spin correctly, which prevents it from safely venting gases and means the boiler has shut down to keep you safe.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

E110

Your boiler is having trouble breathing, which prevents it from safely venting exhaust gases and starting your heating.

High Engineer only £150-350

Parts commonly replaced

  • Air pressure switch
  • Fan assembly
  • Flue seals

Related codes

E121

Your boiler has stopped because its internal sensors have detected that the water inside the system is not circulating correctly.

High Engineer only £150-250

Parts commonly replaced

  • Central heating pump
  • Flow sensor
  • Diverter valve
E127

Your boiler's air pressure sensor is failing to communicate properly, which means the safety system is preventing the burner from lighting to ensure the unit operates safely.

High Engineer only £150-250

Parts commonly replaced

  • Air Pressure Switch
  • Venturi
  • Fan assembly
  • Wiring harness

Related codes

E205

Your boiler has lost the ability to accurately measure the temperature of the water being sent to your radiators, so it has safely shut itself down to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Heating Supply Thermistor
  • Wiring harness to NTC sensor
E218

Your boiler has lost the ability to read the temperature of the water returning to it, so it has shut down as a precaution to prevent overheating.

High Engineer only £120-220

Parts commonly replaced

  • Return thermistor
  • Wiring harness
E278

Your boiler is having trouble measuring its own internal temperature, so it has shut down to prevent it from getting too hot or cold.

High Engineer only £120-200

Parts commonly replaced

  • Supply Temperature Sensor
  • Wiring Harness

Related codes

E279

Your boiler is struggling to accurately measure the temperature of the water returning to it, which prevents it from heating your home or water correctly.

High Engineer only £150-250

Parts commonly replaced

  • Return thermistor sensor
  • Wiring harness

Related codes

E291

Your boiler has detected that the water flow pipes are connected in the wrong order or that the heat is moving in the wrong direction, causing the system to shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • Flow temperature probe
  • Return temperature probe
  • Main PCB
Showing 71–80 of 108
E302

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 internal filling loop (usually a silver braided hose or a plastic linkage under the boiler).
  2. Slowly open the valves to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valves firmly and ensure no water is leaking from the connection points.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Expansion vessel
E351

Your boiler has been trying to refill its internal water supply for too long but has failed to reach the required level.

High Engineer only £150-250

Parts commonly replaced

  • Automatic filling loop valve
  • Pressure sensor
  • Expansion vessel

Related codes

E352

Your boiler has detected that the water pressure inside the heating system is too high for it to operate safely.

High DIY-safe £80-150

What to check first

  1. Locate a radiator in your home with a bleed valve
  2. Open the valve using a radiator key to release a small amount of water into a cloth
  3. Check the boiler pressure gauge until it drops into the green zone (usually between 1.0 and 1.5 bar)
  4. Close the radiator bleed valve tightly

Parts commonly replaced

  • Pressure relief valve
  • Pressure sensor (transducer)
  • Filling loop

Related codes

E353

Your boiler is struggling to accurately read the water pressure inside the system, which is preventing it from firing up safely.

High Engineer only £150-250

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

E407

Your boiler is struggling to detect the temperature of the water for your taps and shower because a sensor has stopped communicating correctly.

High Engineer only £120-220

Parts commonly replaced

  • DHW thermistor
  • Wiring harness
E421

Your boiler is having trouble measuring incoming water temperature due to a faulty sensor, which is currently preventing it from heating your water correctly.

High Engineer only £120-£220

Parts commonly replaced

  • Domestic Hot Water (DHW) sensor
  • Wiring harness

Related codes

E432

Your boiler is struggling to detect when you turn on a hot tap, so it isn't heating the water for your shower or kitchen taps.

Medium Engineer only £150-250

Parts commonly replaced

  • DHW Flow Sensor
  • Wiring harness
E434

Your boiler is struggling to correctly manage the flow of water because an internal component responsible for adjusting water volume has detected an error.

High Engineer only £180-300

Parts commonly replaced

  • Water adjustment valve
  • Flow control motor
  • Main PCB
E439

Your boiler is struggling to detect the flow of water through the system, which means it cannot safely heat your home or provide hot water.

High Engineer only £150-250

Parts commonly replaced

  • Flow sensor
  • Wiring harness

Related codes

E441

Your boiler is having trouble sensing the temperature of your hot water supply, which will likely prevent it from heating your water correctly.

Medium Engineer only £120-220

Parts commonly replaced

  • Domestic Hot Water Thermistor
  • Wiring Harness
Showing 81–90 of 108
E445

Your boiler is having trouble managing the flow of water between your heating system and your hot water taps, which may cause your heating or hot water to stop working properly.

High Engineer only £200-350

Parts commonly replaced

  • Bypass mixing valve
  • Actuator motor
E480

Your boiler is struggling to detect the temperature of your hot water supply because a connection to its temperature sensor has been lost or interrupted.

High Engineer only £120-220

Parts commonly replaced

  • DHW Thermistor
  • Wiring harness
E515

Your boiler's main computer is having trouble processing information and needs to be looked at by a professional.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB
  • Main wiring harness

Related codes

E517

Your boiler's internal configuration settings are currently mismatched, which is preventing it from starting up correctly.

High Engineer only £120-250

Parts commonly replaced

  • Main PCB
E593

Your boiler's electronic control panel is experiencing a communication fault, which prevents the display from responding or controlling the unit properly.

High Engineer only £150-300

Parts commonly replaced

  • Front panel PCB
  • Wiring harness to display
E594

Your boiler's computer memory has encountered a data error, which is preventing it from starting up correctly.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)

Related codes

E595

Your boiler's electronic control board is having trouble talking to the display panel, meaning it cannot currently receive commands or show status updates.

High Engineer only £150-250

Parts commonly replaced

  • Front Control/Display PCB
  • Communication wiring harness

Related codes

E596

Your boiler has lost its digital connection to your room thermostat, meaning it cannot receive signals to turn the heating on or off.

Medium DIY-safe £90-180

What to check first

  1. Switch off the power to the boiler at the fused spur or consumer unit.
  2. Wait 5 minutes to let the system fully reset.
  3. Turn the power back on and check if the thermostat re-establishes its connection with the boiler.

Parts commonly replaced

  • Smart room thermostat unit
  • Communication cable
  • Main PCB

Related codes

E598

Your boiler's internal clock has lost its settings, which usually means the system cannot keep time to manage your heating schedule correctly.

Low DIY-safe

What to check first

  1. Locate the user menu on your boiler's control panel.
  2. Navigate to the date and time settings.
  3. Manually reset the current date and time to clear the error.

Parts commonly replaced

  • Control PCB
  • Internal battery
E615

Your boiler's computer has detected an internal error with its data storage, meaning it cannot reliably operate its settings or programs.

High Engineer only £250-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Control module
Showing 91–100 of 108
E736

Your boiler is struggling to talk to other linked heating units in your system, meaning it cannot coordinate its operation properly.

High Engineer only £150-300

Parts commonly replaced

  • Cascade communication cable
  • PCB board
E740

Your boiler is struggling to read the temperature outside, which means it cannot automatically adjust your heating to match the weather conditions.

Low Engineer only £120-200

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring harness
E761

Your boiler is having trouble detecting the temperature of the water reserved for your hot water system, which may prevent it from heating your taps correctly.

Medium Engineer only £150-250

Parts commonly replaced

  • DHW thermistor
  • Wiring harness
  • Main PCB
E762

Your boiler is struggling to detect the exhaust vent, likely because the flue pipe is not fitted securely or is the wrong size for your home.

High Engineer only £120-250

Parts commonly replaced

  • Flue assembly
  • Vent collar
  • PCB

Related codes

E773

Your boiler has detected that the type of gas being supplied does not match what the boiler is set up to use, meaning it cannot operate safely.

Emergency Engineer only £150-300

Parts commonly replaced

  • Gas valve
  • PCB (Printed Circuit Board)
E777

Your boiler has detected that a safety device installed outside the main unit is reporting a dangerously low water level, preventing the boiler from starting to protect it from damage.

High Engineer only £150-300

Parts commonly replaced

  • Low Water Cut Off switch
  • External flow switch
  • Wiring harness
E782

Your boiler's main control panel is failing to communicate with the internal system, which will prevent your heating and hot water from working properly.

High Engineer only £150-350

Parts commonly replaced

  • Main PCB
  • Communication wiring harness
  • Control interface unit

Related codes

E783

Your boiler is having trouble communicating with your wall-mounted thermostat or smart control system, which prevents it from knowing when to turn on your heating.

High Engineer only £120-250

Parts commonly replaced

  • OpenTherm interface module
  • PCB
  • Communication wiring
E784

Your boiler is having trouble communicating with the external controls or zoning system that tells it when to heat each area of your home.

High Engineer only £150-300

Parts commonly replaced

  • Zone controller board
  • Communication wiring harness
  • Main PCB
E785

Your boiler is struggling to detect the water flow or pressure levels, which is likely preventing it from starting up properly.

High Engineer only £180-350

Parts commonly replaced

  • Flow sensor
  • Pressure sensor
  • Wiring harness

Related codes

Showing 101–108 of 108
E786

Your boiler's front cover is not properly attached or secured, which acts as a safety disconnect to prevent the unit from running while it is open.

Medium DIY-safe

What to check first

  1. Switch off the power to the boiler
  2. Remove the front cover and ensure no wires are pinched
  3. Replace the front cover, ensuring it is flush and firmly locked in place with all screws tightened

Related codes

E787

Your boiler has detected a minor internal software or communication glitch and needs to be restarted to clear the error.

Medium DIY-safe £90-180

What to check first

  1. Locate the power switch or the fuse spur supplying the boiler.
  2. Turn the boiler power off and wait for at least 60 seconds.
  3. Turn the power back on and see if the error code clears itself.

Parts commonly replaced

  • Main PCB
  • Wiring harness

Related codes

E788

Your boiler has detected an issue with the amount of gas it is receiving or the settings used to burn it, which prevents it from operating safely.

Emergency Engineer only £150-350

Parts commonly replaced

  • Gas valve
  • PCB (Printed Circuit Board)
  • Gas regulator
E792

Your boiler is struggling to circulate hot water properly, which means it cannot reliably provide hot water to your taps or showers.

High Engineer only £150-300

Parts commonly replaced

  • DHW pump
  • Flow sensor
  • Diverter valve

Related codes

Ignition failure

Your boiler is failing to light the internal flame, which means it cannot produce any hot water or heating for your home.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Ignition transformer
  • Gas valve

Related codes

Q-Error

Your boiler's computer does not recognise which specific version of the appliance is installed, preventing it from functioning correctly.

High Engineer only £100-£200

Parts commonly replaced

  • Main PCB

Related codes

Repeated ignition failure

Your boiler is struggling to light its internal flame, which means it has automatically shut down to prevent gas from building up.

High Engineer only £150-350

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame sensor
  • Fan assembly

Related codes

TEC

Your boiler has reached its programmed time for a routine annual service as a reminder to ensure it remains safe and efficient.

Low Engineer only £90-140