Baxi 200 Combi 2 Fault codes & diagnostics

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

Combi Natural GasLPG 2016-present
GC Numbers 47-077-2347-077-2447-077-4847-077-4947-077-50
Download the Baxi 200 Combi 2 manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

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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.
1 Emergency 41 High 4 Medium 2 Low
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
47-077-23 400 424 COMBI 2016–present
47-077-24 400 428 COMBI 2016–present
Just want the most common Baxi 200 Combi 2 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 48 documented codes

Tap any card for details

A.00.34

Your boiler is looking for an outdoor weather sensor that it can no longer communicate with, which might cause your heating to behave unpredictably.

Low DIY-safe £90-160

What to check first

  1. Check if any external wires on the outside of your house leading to a small plastic box have been damaged or cut.
  2. Try resetting the boiler by pressing the 'R' or Reset button for five seconds.
  3. If you recently had building work near the boiler or outside walls, check if the sensor was accidentally unplugged.

Parts commonly replaced

  • Outdoor temperature sensor
  • Wiring harness
  • Sensor cable

Related codes

Full explanation for A.00.34
A.02.06

Your boiler has detected that there is not enough water in the central heating system to operate safely.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (the silver braided hose) underneath the boiler.
  2. Slowly open the blue or black taps on the filling loop until you hear water flowing.
  3. Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for A.02.06
A.02.36

Your boiler has lost communication with one of its internal control components, meaning it cannot operate safely and has shut itself down.

High Engineer only £120-£350

Parts commonly replaced

  • Wiring harness
  • Printed Circuit Board (PCB)
  • Low pressure switch

Related codes

Full explanation for A.02.36
A.02.55

Your boiler's internal computer has lost its identification data or is not communicating correctly with its main control board.

High Engineer only £120-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Data Key

Related codes

Full explanation for A.02.55
E.00.04

Your boiler has lost its connection to the sensor that monitors water returning from your radiators, causing the system to stop working as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Return NTC thermistor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for E.00.04
E.00.05

Your boiler has detected a fault with the sensor that measures the temperature of the water returning to the unit, causing it to stop running as a safety precaution.

High Engineer only £90-160

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Wiring harness

Related codes

Full explanation for E.00.05
E.00.16

Your boiler is unable to read the temperature of your hot water cylinder, which means you may not have reliable hot water.

High Engineer only £90-180

Parts commonly replaced

  • DHW Tank Temperature Sensor (NTC)
  • Connection wiring/harness

Related codes

Full explanation for E.00.16
E.00.17

Your boiler has detected a fault with the sensor that monitors your hot water temperature, meaning it cannot safely heat your water to the correct level.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW temperature sensor (NTC thermistor)
  • Sensor wiring harness

Related codes

Full explanation for E.00.17
E.00.20

Your boiler has detected an issue with the sensor that monitors the safety of exhaust gases, causing the system to shut down for protection.

High Engineer only £120-£200

Parts commonly replaced

  • Flue gas temperature sensor (NTC)
  • Wiring harness
  • Main circuit board (PCB)

Related codes

Full explanation for E.00.20
E.00.21

Your boiler has detected that the exhaust gases are getting too hot or the internal sensor that monitors them has developed a wiring fault, causing the system to shut down for safety.

High Engineer only £120-£220

Parts commonly replaced

  • Flue Gas Temperature Sensor
  • Sensor Wiring Harness
  • Main Heat Exchanger

Related codes

Full explanation for E.00.21
Showing 11–20 of 48
E.01.04

Your boiler is repeatedly struggling to keep the flame lit while it is running, causing it to shut down for safety after multiple failures.

High DIY-safe £120-350

What to check first

  1. Check that your gas pre-payment meter has credit
  2. Ensure other gas appliances in your home, like a hob, are working correctly
  3. Reset the boiler by pressing the 'R' or 'Reset' button

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for E.01.04
E.01.12

Your boiler has sensed that the water returning from your radiators is hotter than the water leaving the boiler, which usually means there is a circulation problem or a sensor fault.

High DIY-safe £90-220

What to check first

  1. Ensure all radiator valves (TRVs) are fully open
  2. Check that the boiler pressure is between 1.0 and 1.5 bar
  3. Press the Reset button for five seconds

Parts commonly replaced

  • Return temperature sensor (NTC thermistor)
  • Flow temperature sensor
  • Central heating pump

Related codes

Full explanation for E.01.12
E.01.17

Your boiler has detected that water is not moving through the system properly, which has caused it to shut down to prevent overheating.

High DIY-safe £100-£350

What to check first

  1. Check the pressure gauge and top it up to 1.5 bar using the filling loop if it is too low
  2. Ensure all radiator valves are fully open
  3. Check for any visible leaks around your pipework
  4. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation Pump
  • Water Pressure Sensor
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for E.01.17
E.01.20

Your boiler has sensed that the exhaust gases are getting too hot and has shut itself down as a safety precaution.

High Engineer only £150-350

Parts commonly replaced

  • Main Heat Exchanger
  • Heat Exchanger NTC Sensor
  • Flue Thermostat

Related codes

Full explanation for E.01.20
E.02 .13

Your boiler has shut down completely to protect itself from damage because it is not detecting the necessary water circulation to function safely.

High Engineer only £150-300

Parts commonly replaced

  • Circulation pump
  • Flow sensor
  • Main PCB

Related codes

Full explanation for E.02 .13
E.02 .35

Your boiler has detected that a vital safety component is not communicating correctly and has shut down to prevent any risk.

Emergency Engineer only £120-250

Parts commonly replaced

  • Safety sensor
  • Wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E.02 .35
E.02 .39

Your boiler has detected that the water pressure is too low to operate safely, and it was unable to top itself up automatically.

High DIY-safe £90-180

What to check first

  1. Locate the external filling loop, usually found underneath the boiler.
  2. Open the valves slowly to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close both valves tightly to prevent over-pressurisation.

Parts commonly replaced

  • Filling loop
  • Pressure sensor
  • Primary flow switch

Related codes

Full explanation for E.02 .39
E.02 .47

Your boiler is having trouble communicating with an add-on device like a room thermostat or a smart heating controller.

Medium Engineer only £100-250

Parts commonly replaced

  • External controls interface
  • Wiring harness
  • PCB

Related codes

Full explanation for E.02 .47
E.02.17

Your boiler has stopped working because the internal control board and the gas valve have lost the ability to talk to each other.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB
  • Gas Valve
  • Wiring Harness

Related codes

Full explanation for E.02.17
E.04 .29

Your boiler's internal computer is having trouble talking to its own parts, causing the system to stop working entirely.

High Engineer only £150-300

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Full explanation for E.04 .29
Showing 21–30 of 48
E.04.01

Your boiler has detected a fault with the internal sensor that monitors the temperature of the water leaving the unit, meaning it cannot safely regulate heat.

High Engineer only £90-160

Parts commonly replaced

  • Flow Temperature Sensor (NTC Thermistor)
  • Wiring Harness

Related codes

Full explanation for E.04.01
E.04.02

Your boiler has lost communication with the internal thermometer that monitors water leaving the unit, causing the system to shut down for safety.

High Engineer only £100-180

Parts commonly replaced

  • Flow Temperature Sensor (NTC thermistor)
  • Wiring harness
  • Main PCB

Related codes

Full explanation for E.04.02
E.04.03

Your boiler has shut down because it thinks it is getting too hot or it has detected a technical fault with its internal temperature sensor.

High DIY-safe £90-180

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1 and 1.5 bar on the gauge
  3. Turn the boiler off and back on again to attempt a reset

Parts commonly replaced

  • Temperature Flow Sensor (NTC)
  • Circulation Pump
  • Main Heat Exchanger cleaning

Related codes

Full explanation for E.04.03
E.04.08

Your boiler has shut down because the water inside has become far too hot, likely due to a circulation problem.

High DIY-safe £120-£350

What to check first

  1. Check that your radiator valves are fully open
  2. Ensure there is enough water pressure in the system (usually between 1.0 and 1.5 bar on the gauge)
  3. Try resetting the boiler by turning the selector knob to 'R' for five seconds

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Main Heat Exchanger (Cleaning/Flushing)

Related codes

Full explanation for E.04.08
E.04.10

Your boiler has tried and failed to light its burner four times, meaning it cannot provide heating or hot water until the issue is resolved.

High DIY-safe £120-350

What to check first

  1. Check if your gas supply is active by testing another gas appliance like a hob
  2. Ensure your gas meter has credit and the handle is in the 'on' position
  3. Press the 'Reset' button on the boiler control panel for five seconds

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Electrode
  • Condensate Trap/Pipe

Related codes

Full explanation for E.04.10
E.04.12

Your boiler is detecting a flame when there shouldn't be one, so it has shut down as a safety precaution.

High Engineer only £120-280

Parts commonly replaced

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

Related codes

Full explanation for E.04.12
E.04.13

Your boiler's fan, which clears exhaust gases, is struggling to spin at the correct speed or is being physically obstructed.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E.04.13
E.04.17

Your boiler has detected an internal electrical problem with the component that controls the gas supply, meaning it cannot safely light itself to provide heat or hot water.

High Engineer only £180-350

Parts commonly replaced

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

Related codes

Full explanation for E.04.17
E.04.18

Your boiler has detected that a temperature sensor is either disconnected or reading an unusually cold temperature, preventing it from heating your home safely.

High Engineer only £90-180

Parts commonly replaced

  • Flow NTC sensor
  • Wiring harness
  • Control PCB

Related codes

Full explanation for E.04.18
E.04.23

Your boiler has lost connection with its gas control unit, meaning it cannot safely release fuel to start the flame.

High Engineer only £220-450

Parts commonly replaced

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

Related codes

Full explanation for E.04.23
Showing 31–40 of 48
H.00.42

Your boiler has stopped working because it cannot correctly detect the water pressure, likely due to a faulty internal sensor or a broken connection.

High Engineer only £140-£220

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness

Related codes

Full explanation for H.00.42
H.01.00

Your boiler has stopped working because the internal control board and the gas supply valve are temporarily failing to talk to each other.

High Engineer only £150-£450

Parts commonly replaced

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

Related codes

Full explanation for H.01.00
H.01.05

Your boiler has detected that water is leaving the unit much hotter than when it returns, suggesting that the water isn't circulating through your radiators properly.

High DIY-safe £120-£350

What to check first

  1. Ensure all radiator valves (TRVs) are fully open
  2. Check that the boiler pressure is between 1 and 1.5 bar on the gauge
  3. Bleed all radiators to remove trapped air pockets

Parts commonly replaced

  • Circulation Pump
  • Central Heating Filter (Cleaning)
  • Main Heat Exchanger (Flushing)

Related codes

Full explanation for H.01.05
H.01.08

Your boiler is heating up too quickly and has temporarily shut down to prevent overheating, usually because the water cannot circulate properly through your radiators.

High DIY-safe £80-250

What to check first

  1. Check that your boiler pressure is between 1 and 1.5 bar on the gauge.
  2. Ensure at least two or three radiators have their valves fully open.
  3. Bleed your radiators to remove any trapped air that might be blocking water flow.

Parts commonly replaced

  • Central heating pump
  • Magnetic system filter (cleaning)
  • Main heat exchanger (flushing)

Related codes

Full explanation for H.01.08
H.01.14

Your boiler has shut down because it has detected that the water inside has become too hot, usually due to a lack of circulation.

High DIY-safe £120-350

What to check first

  1. Ensure all radiator valves (TRVs) are turned to the highest setting
  2. Check that the boiler pressure is between 1 and 1.5 bar on the gauge
  3. Wait 30 minutes for the unit to cool down and press the Reset button

Parts commonly replaced

  • Central heating pump
  • Temperature thermistor (NTC sensor)
  • Main heat exchanger (flushing/cleaning)

Related codes

Full explanation for H.01.14
H.01.18

Your boiler has detected that water is not moving through the system properly, often because the water pressure is too low.

High DIY-safe £0-120

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. Locate the filling loop (the silver braided hose) underneath the boiler.
  3. Open the valves slowly to top up the water pressure until the gauge reaches 1.2 bar, then close them tightly.
  4. Restart the boiler to clear the fault.

Parts commonly replaced

  • N/A (Usually just a pressure top-up)
  • Filling loop valve
  • Expansion vessel

Related codes

Full explanation for H.01.18
H.01.21

Your boiler is heating up too quickly when you turn on the hot water, causing it to shut down to prevent damage.

High Engineer only £120-£350

Parts commonly replaced

  • Plate Heat Exchanger
  • Diverter Valve
  • Central Heating Pump

Related codes

Full explanation for H.01.21
H.02.00

Your boiler is currently restarting itself or finishing a reset cycle and should return to normal operation shortly.

Low DIY-safe £0

What to check first

  1. Wait up to 5 minutes for the countdown or reset process to complete
  2. Ensure any 'Reset' buttons are not stuck in the pressed position
  3. If the code persists for more than 10 minutes, try turning the main power switch off and back on

Related codes

Full explanation for H.02.00
H.02.02

Your boiler is basically stuck in 'setup mode' because its main control board is waiting for essential configuration codes to be programmed in.

High Engineer only £90-180

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for H.02.02
H.02.03

Your boiler’s internal computer has lost its specific identity settings and needs to be told exactly which model it is before it can operate.

High Engineer only £100-£250

Parts commonly replaced

  • Printed Circuit Board (PCB)

Related codes

Full explanation for H.02.03
Showing 41–48 of 48
H.02.04

Your boiler's main control board is having trouble reading its own saved internal settings, which is preventing the system from starting up.

High Engineer only £280-500

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Configuration Key

Related codes

Full explanation for H.02.04
H.02.05

Your boiler’s internal control board is confused because its software does not match the hardware installed, often following a repair or a power glitch.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Parameters Key

Related codes

Full explanation for H.02.05
H.02.07

Your boiler has detected that the water pressure in your radiators is too low for the system to work safely, so it has turned itself off.

High DIY-safe £0-120

What to check first

  1. Locate the flexible filling loop under the boiler with the two blue-handled taps.
  2. Slowly open both taps one at a time until you hear water flowing.
  3. Watch the pressure gauge on the front of the boiler until it reaches between 1.0 and 1.5 bar, then close both taps fully.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for H.02.07
H.02.09

Your boiler has detected low water flow and has automatically turned on its frost protection mode to prevent the system from seizing or freezing.

Medium DIY-safe £0-120

What to check first

  1. Check that your boiler pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves are fully open
  3. Check the condensate pipe outside for signs of freezing or blockage
  4. Restart the boiler using the reset button

Parts commonly replaced

  • System filter (cleaning)
  • Circulation pump
  • Pressure sensor

Related codes

Full explanation for H.02.09
H.02.10

Your boiler has shut down completely and its internal protection against freezing is no longer working, meaning your pipes could be at risk if the weather is very cold.

High Engineer only £150-350

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Internal Wiring Harness

Related codes

Full explanation for H.02.10
H.03.00

Your boiler's main control board is unable to communicate with its internal safety chip, meaning the boiler has disabled itself for protection.

High Engineer only £180-350

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Safety Key
  • Wiring Harness

Related codes

Full explanation for H.03.00
H.03.02

Your boiler's burner has unexpectedly gone out while running, causing the system to restart or stop to ensure safety.

Medium DIY-safe £80-250

What to check first

  1. Check that your gas pre-pay meter has credit (if applicable)
  2. Check that other gas appliances in your home are working correctly
  3. Press the Reset button for five seconds
  4. Ensure the external condensate pipe is not frozen if it is currently cold weather

Parts commonly replaced

  • Ionisation probe
  • Ignition electrode
  • Gas valve

Related codes

Full explanation for H.03.02
H.03.05

Your boiler is not receiving enough electrical power from your home's mains supply to operate safely.

High DIY-safe £100-£350

What to check first

  1. Check if there is a partial power cut or 'brownout' in your local area
  2. Ensure the boiler's fused spur switch is fully engaged and not damaged
  3. Switch the boiler off at the main spur, wait 30 seconds, and switch it back on to reset the electronics

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • External Voltage Stabiliser
  • Main Power Cable

Related codes

Full explanation for H.03.05
Status & diagnostic codes

11 operating states & engineer diagnostics

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

A.00 .28 Diagnostic Your boiler is struggling to read the temperature from an optional solar water heating accessory that may not be connected or has a loose wire. A.00 .29 Diagnostic Your boiler is detecting an incorrect reading from the solar water heating sensor, which is preventing the system from operating correctly. A.02 .37 Diagnostic Your boiler has lost its connection to an essential internal sensor, meaning it cannot safely monitor its own operation and has shut down to protect itself. A.02 .45 Diagnostic Your boiler's internal computer is struggling to communicate with its own components, which is preventing the system from running safely and effectively. A.02 .46 Diagnostic Your boiler is experiencing a communication error where it cannot decide whether to prioritize heating your home or heating your water. A.02 .48 Diagnostic Your boiler's internal computer is struggling to recognise the specific settings it needs to run, causing it to stop functioning correctly. A.02 .49 Diagnostic Your boiler's internal computer system is having trouble starting up and communicating with its internal components, causing it to shut down for safety. A.02 .54 Diagnostic Your boiler is having a communication breakdown with its internal control system, which prevents it from operating correctly. A.02 .76 Diagnostic Your boiler is experiencing a software or internal memory communication error that is preventing it from operating correctly. H.02 .70 Diagnostic Your boiler's internal computer is struggling to communicate with an optional add-on part, which is preventing the system from operating correctly. H.03 .54 Diagnostic Your boiler has automatically shut down because the electricity supply coming into your home is not stable or powerful enough to keep it running safely.
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