Baxi EcoBlue Advance Heat Fault codes & diagnostics

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

Regular Natural Gas 13-30 kW 2014 onwards Discontinued
GC Numbers 41-470-3441-470-3541-470-3641-470-3741-470-38
Download the Baxi EcoBlue Advance Heat manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

This boiler uses LED flash patterns

Count the flashes in one repeating group before the pause. That number is your fault code. Do not reset until you have noted it. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
33 High 2 Medium 4 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
41-470-34 EcoBlue Advance 13 Heat ErP 2014–present
41-470-35 EcoBlue Advance 16 Heat ErP 2014–present
41-470-36 EcoBlue Advance 19 Heat ErP 2014–present
41-470-37 EcoBlue Advance 25 Heat ErP 2014–present
41-470-38 EcoBlue Advance 30 Heat ErP 2014–present
Just want the most common Baxi EcoBlue Advance Heat faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 39 documented codes

Tap any card for details

LED / flash-pattern codes
1 flash green

Your boiler is overheating because water is not moving through the system quickly enough to be cooled down.

High DIY-safe £100-350

What to check first

  1. Check that your radiator valves are turned on and not closed.
  2. Ensure your external heating pump is running if you have one.
  3. Try resetting the boiler by turning the selector switch to 'R' and then back to 'On'.

Parts commonly replaced

  • Circulation pump
  • Heat exchanger (cleaning/flush)
  • Thermistor (NTC sensor)

Related codes

Full explanation for 1 flash green
1 flash red

Your boiler has detected a problem with how water is moving through the system or a fault with the sensors that monitor temperature.

High DIY-safe £90-220

What to check first

  1. Check that all radiator valves are open
  2. Ensure the external system pump is running (if accessible)
  3. Check that the boiler pressure is between 1 and 1.5 bar
  4. Reset the boiler by turning the selector switch to 'R' for five seconds

Parts commonly replaced

  • Flow temperature sensor (NTC)
  • Return temperature sensor (NTC)
  • External central heating pump

Related codes

Full explanation for 1 flash red
1 red flash

Your boiler has detected that it is getting too hot or that water isn't moving through the system correctly, causing it to shut down for safety.

High DIY-safe £120-250

What to check first

  1. Check that your radiator valves are open
  2. Ensure your system water pressure is between 1 and 1.5 bar on the gauge
  3. Reset the boiler by turning the selector switch to 'R' for five seconds

Parts commonly replaced

  • Temperature Sensor (NTC Thermistor)
  • Circulating Pump
  • Overheat Thermostat

Related codes

Full explanation for 1 red flash
2 flashes green

Your boiler has received an external signal to turn off, usually triggered by an connected thermostat, safety device, or a loose wiring connection.

High DIY-safe £80-180

What to check first

  1. Check if your room thermostat or programmer is turned on and set to a temperature higher than the current room temperature.
  2. Replace the batteries in your room thermostat if it uses them.
  3. Check your fuse box to ensure no heating-related switches have tripped.

Parts commonly replaced

  • External Room Thermostat
  • Wiring Link/Jumper
  • User Interaction Controller

Related codes

Full explanation for 2 flashes green
2 flashes red

Your boiler has sensed it is getting too hot and has shut down as a safety precaution to prevent damage.

High DIY-safe £120-350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure there is no air trapped in the system by bleeding your radiators.
  3. Press the reset button or turn the selector switch to 'R' for five seconds to see if the fault clears.

Parts commonly replaced

  • Over-heat thermostat
  • Circulation pump
  • Heat exchanger sensor

Related codes

Full explanation for 2 flashes red
2 red flashes

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

High DIY-safe £100-£350

What to check first

  1. Check that your radiator valves are open and not turned to zero.
  2. Ensure your system water pressure is between 1 and 1.5 bar on the gauge.
  3. Turn the selector switch to the reset position for five seconds and then back to 'onn'.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • Main Heat Exchanger (Flushing)

Related codes

Full explanation for 2 red flashes
3 flashes green

Your boiler was working but the flame has unexpectedly gone out, causing the system to stop as a safety precaution.

High DIY-safe £100-£280

What to check first

  1. Check if other gas appliances (like a hob) are working to ensure your gas supply is active
  2. Check that your gas meter has credit if you use a prepay meter
  3. Press and hold the reset button for five seconds
  4. Check for any frozen external condensate pipes if it is currently freezing weather

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead

Related codes

Full explanation for 3 flashes green
3 flashes red

Your boiler is failing to light the gas or cannot stay lit, meaning you currently have no heating or hot water.

High DIY-safe £100-280

What to check first

  1. Check that your gas pre-payment meter (if you have one) has credit.
  2. Verify that other gas appliances in your home, like a hob, are working correctly.
  3. Reset the boiler by turning the selector switch to the 'R' position for five seconds and then back to its original setting.

Parts commonly replaced

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

Related codes

Full explanation for 3 flashes red
3 green flashes

Your boiler has briefly lost its flame and is trying to restart itself, which is often a temporary glitch that might resolve without any action.

Low DIY-safe £100-250

What to check first

  1. Monitor the boiler to see if it clears the fault automatically
  2. Check that other gas appliances (like a hob) are working correctly
  3. Ensure the condensate pipe has not frozen if it is cold outside
  4. Reset the boiler if the flashes turn red

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for 3 green flashes
3 red flashes

Your boiler has tried to light itself several times but cannot establish a flame, meaning you will have no heating or hot water until it is reset or repaired.

High DIY-safe £120-280

What to check first

  1. Check if other gas appliances in your home, like a hob, are working to ensure gas is reaching the property
  2. Check that your gas meter has credit if you use a pre-payment system
  3. Press and hold the reset button for five seconds to see if the boiler restarts

Parts commonly replaced

  • Ignition Electrode
  • Gas Valve
  • Flame Sensing Lead
  • Printed Circuit Board (PCB)
Full explanation for 3 red flashes
Showing 11–20 of 39
4 flashes green

Your boiler is having trouble sending messages between its internal electronic parts, meaning it cannot start up to provide heating or hot water.

High Engineer only £100-£350

Parts commonly replaced

  • Main PCB (Control Board)
  • Wiring Harness
  • Display Board

Related codes

Full explanation for 4 flashes green
4 flashes red

Your boiler's fan, which safely pushes exhaust gases out of the flue, is not spinning at the correct speed or has stopped working entirely.

High Engineer only £250-£450

Parts commonly replaced

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

Related codes

Full explanation for 4 flashes red
4 green flashes

Your boiler is having a temporary 'handshake' issue between its internal electronic brains, but it should fix itself automatically.

Low DIY-safe £0-120

What to check first

  1. Wait for the boiler to self-reset as this is often a temporary glitch
  2. If the flashing continues, turn the selector switch to 'Reset' for five seconds
  3. Monitor the boiler to see if the green flashes return

Parts commonly replaced

  • None (usually self-correcting)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 4 green flashes
4 red flashes

Your boiler's fan is not spinning or communicating correctly with the system, preventing the boiler from starting safely.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 4 red flashes
5 flashes green

Your boiler’s internal computer chip or control board has encountered a software configuration error and cannot start up.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB
  • Parameter Plug

Related codes

Full explanation for 5 flashes green
5 flashes red

Your boiler's internal computer is having difficulty communicating with its main control unit, meaning it cannot process the settings needed to run safely.

High Engineer only £180-450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness
  • Parameter Plug

Related codes

Full explanation for 5 flashes red
5 green flashes

Your boiler has experienced a brief digital hiccup or settings error and is attempting to fix itself automatically.

Low DIY-safe £0-350

What to check first

  1. Wait for the boiler to complete its automatic self-reset process
  2. Monitor the display to see if the flashing stops naturally
  3. If the flashing continues for more than 10 minutes, try turning the boiler off and back on at the fused spur switch

Parts commonly replaced

  • None (Software reset)
  • Printed Circuit Board (PCB)

Related codes

Full explanation for 5 green flashes
5 red flashes

Your boiler's internal memory chip has developed a communication fault, meaning the control board can no longer read its essential settings.

High Engineer only £120-250

Parts commonly replaced

  • Parameter Storage Unit (PSU)
  • Printed Circuit Board (PCB)
Full explanation for 5 red flashes
6 flashes green

Your boiler's internal computer has encountered a processing error and cannot safely manage the burner.

High Engineer only £280-450

Parts commonly replaced

  • Main Printed Circuit Board (PCB)
  • Control Unit Wiring Loom

Related codes

Full explanation for 6 flashes green
6 flashes red

Your boiler has stopped working because its internal components are struggling to talk to each other or have detected a sequence error.

High Engineer only £100-£350

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring Harness
  • External Controls

Related codes

Full explanation for 6 flashes red
Showing 21–30 of 39
6 green flashes

Your boiler has encountered a minor glitch and is attempting to restart itself automatically without you needing to do anything.

Low DIY-safe £0-120

What to check first

  1. Wait up to 15 minutes for the boiler to complete its self-reset process
  2. Ensure the boiler's electrical supply is stable and not fluctuating
  3. Turn the selector switch to 'Reset' and back to 'On' if the light continues to flash

Parts commonly replaced

  • No parts usually required
  • Control PCB
Full explanation for 6 green flashes
6 red flashes

Your boiler has detected an internal communication or unexpected component fault and has stopped working as a safety precaution.

High DIY-safe £100-£350

What to check first

  1. Turn the selector switch to the 'Reset' position and hold for 5 seconds.
  2. Release the switch and wait for the boiler to attempt to restart.
  3. Ensure your gas supply is active and your credit meter (if applicable) has funds.

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness
  • Gas Valve
Full explanation for 6 red flashes
Digital codes
20

Your boiler's temperature sensor has encountered a technical glitch, meaning the system cannot accurately measure how hot the water is for your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating NTC Sensor
  • Sensor Wiring Harness

Related codes

Full explanation for 20
28

Your boiler has detected a problem with the sensor that monitors the temperature of the exhaust gases, causing the system to shut down for safety.

High Engineer only £100-£190

Parts commonly replaced

  • Flue NTC Thermistor
  • Wiring Harness
  • Main PCB

Related codes

Full explanation for 28
40

Your boiler has detected an issue with the sensor that monitors the temperature of the water returning from your radiators.

High Engineer only £90-160

Parts commonly replaced

  • Central Heating Return NTC Thermistor
  • Wiring Harness

Related codes

Full explanation for 40
109

Your boiler has sensed that the water inside isn't moving properly and has shut down to prevent itself from overheating.

High DIY-safe £150-£350

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the system pressure is within the green zone (usually 1.0 to 1.5 bar)
  3. Turn the boiler off and back on to see if the fault clears after cooling

Parts commonly replaced

  • Circulation Pump
  • Flow/Return Temperature Sensors
  • Internal Diverter Valve

Related codes

Full explanation for 109
110

Your boiler has switched itself off because it has reached too high a temperature, likely due to trapped air or a blockage stopping water from circulating.

High DIY-safe £100-250

What to check first

  1. Turn off the boiler and allow it to cool down completely.
  2. Use a radiator key to bleed all radiators to remove any trapped air.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it has dropped.
  4. Turn the boiler back on and press the 'Reset' button.

Parts commonly replaced

  • Overheat Thermostat
  • Circulating Pump
  • NTC Temperature Sensor
Full explanation for 110
111

Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage or potential danger.

High Engineer only £150-300

Parts commonly replaced

  • Safety Thermostat
  • Pump
  • Diverter Valve
  • Heat Exchanger

Related codes

Full explanation for 111
117

Your boiler has too much water in the system, which puts extra stress on the internal parts and may cause it to shut down for safety.

Medium DIY-safe £80-160

What to check first

  1. Check that the internal or external filling loop valves are tightly closed
  2. Bleed water from a radiator using a bleed key to reduce system pressure
  3. Monitor the pressure gauge until it returns to the normal range (typically 1.0 to 1.5 bar)
  4. Restart the boiler if the fault code does not clear automatically

Parts commonly replaced

  • Filling loop valve
  • Pressure Relief Valve (PRV)
  • Expansion vessel

Related codes

Full explanation for 117
118

Your boiler has detected that there is not enough water in the system to operate safely, causing it to shut down temporarily.

High DIY-safe £0-120

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Slowly open the one or two taps/valves on the filling loop until you hear water entering the system.
  3. Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.

Parts commonly replaced

  • Filling loop valves
  • Expansion vessel
  • Pressure sensor

Related codes

Full explanation for 118
Showing 31–39 of 39
125

Your boiler has detected that water isn't moving through the system properly, which is causing it to overheat and shut down for safety.

High DIY-safe £150-£350

What to check first

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

Parts commonly replaced

  • Circulating Pump
  • Pump Lead
  • Main Heat Exchanger

Related codes

Full explanation for 125
128

Your boiler started to heat up but the flame went out unexpectedly while it was running.

High DIY-safe £100-£350

What to check first

  1. Check that your gas pre-pay meter has credit
  2. Ensure other gas appliances in your home are working to confirm gas supply
  3. Press the 'Reset' button for five seconds

Parts commonly replaced

  • Flame sensing electrode
  • Ignition lead
  • Gas valve

Related codes

Full explanation for 128
130

Your boiler has shut down because it detected that the exhaust gases are getting too hot, which could indicate a blockage or a safety issue.

High Engineer only £120-250

Parts commonly replaced

  • Flue NTC Sensor
  • Heat Exchanger (cleaning/descaling)
  • Main PCB

Related codes

Full explanation for 130
133

Your boiler has tried to ignite but failed to stay alight, which is often caused by a lack of gas supply or a blocked condensation pipe.

High DIY-safe £100-£350

What to check first

  1. Check that your gas supply is turned on and you have credit on your meter.
  2. During freezing weather, check if your external white plastic condensate pipe is frozen and thaw it with warm water.
  3. Press the Reset button for five seconds.

Parts commonly replaced

  • Gas Valve
  • Ignition Electrode
  • Printed Circuit Board (PCB)
Full explanation for 133
151

Your boiler has failed to stay lit or ignite correctly, meaning your heating and hot water will not work until it is reset or repaired.

High DIY-safe £100-£250

What to check first

  1. Press the Reset button for five seconds
  2. Check that your gas meter has credit and the isolation valve is open
  3. Ensure other gas appliances in your home are working correctly

Parts commonly replaced

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

Related codes

Full explanation for 151
160

Your boiler's fan is not spinning at the correct speed, which prevents the system from safely clearing exhaust fumes and starting the ignition process.

High Engineer only £250-£450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 160
321

Your boiler's hot water sensor has developed a fault or disconnected, meaning the system cannot accurately measure the water temperature.

Medium Engineer only £90-160

Parts commonly replaced

  • Hot Water NTC thermistor
  • Wiring harness
Full explanation for 321
384

Your boiler thinks there is a flame present when it is supposed to be off, causing it to shut down for safety.

High Engineer only £120-350

Parts commonly replaced

  • Flame sensing electrode
  • PCB (Printed Circuit Board)
  • Gas valve

Related codes

Full explanation for 384
E118

Your boiler has detected that the water pressure in the heating system is too low to operate safely, which is often caused by a small leak or the need to top up the water.

High DIY-safe £0-160

What to check first

  1. Locate the external filling loop, which is usually a flexible silver hose with two small valves.
  2. Slowly open both valves to allow water into the system while watching the pressure gauge.
  3. Close both valves tightly once the pressure gauge reaches between 1.0 and 1.5 bar.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E118
Status & diagnostic codes

1 operating states & engineer diagnostics

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

1 green flash Status Your boiler has reached the correct temperature and is simply taking a natural rest; it is working exactly as it should.