Baxi Assure Fault codes & diagnostics

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

Combi Natural Gas 24-36 kW 2020-present
GC Numbers 47-077-4247-077-4347-077-4447-077-4547-077-4647-077-4747-077-5947-077-6047-077-61
Download the Baxi Assure manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

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

Severity at a glance

Each cell = one fault code. Hover to identify.
16 High 1 Medium 2 Low

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
47-077-42 ASSURE 25 COMBI 2020–present
47-077-43 ASSURE 30 COMBI 2020–present
47-077-44 ASSURE 36 COMBI 2020–present
47-077-45 ASSURE 25 COMBI LPG 2020–present
47-077-46 ASSURE 30 COMBI LPG 2020–present
47-077-47 ASSURE 36 COMBI LPG 2020–present
47-077-59 ASSURE 524 COMBI 2 2023–present
47-077-60 ASSURE 530 COMBI 2 2023–present
47-077-61 ASSURE 536 COMBI 2 2023–present

All 19 documented codes

Tap any card for details

09

Your boiler has detected a temporary internal issue that has caused it to stop working, but it can likely be resolved by a simple manual reset.

Medium DIY-safe £80-120

What to check first

  1. Locate the reset button on the front control panel.
  2. Press and hold the reset button for approximately 3 seconds.
  3. Wait a few minutes to see if the boiler restarts and the fault code disappears.

Parts commonly replaced

  • None
  • Printed Circuit Board (PCB)

Related codes

15

Your boiler has experienced a temporary glitch and needs to be manually restarted to get it back up and running.

Low DIY-safe

What to check first

  1. Locate the 'Reset' button on the front control panel of your boiler.
  2. Press and hold the button for 2 to 3 seconds.
  3. Wait a few minutes to see if the boiler fires up and the fault code clears.

Related codes

20

Your boiler has detected an internal communication error between its internal parts, meaning it has safely shut itself down to prevent potential damage.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

28

Your boiler is struggling to read its own internal water temperature correctly, which is preventing it from heating your home or water safely.

High Engineer only £150-250

Parts commonly replaced

  • NTC Sensor
  • Wiring harness
  • Printed Circuit Board

Related codes

40

Your boiler has detected a general internal fault that is preventing it from starting up correctly.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

103

Your boiler's communication system with its optional safety add-ons is experiencing a glitch, causing the unit to stop working as a precaution.

High Engineer only £120-250

Parts commonly replaced

  • Safety Assist accessory module
  • Wiring harness
  • PCB

Related codes

104

Your boiler's internal safety communication system is experiencing a fault, which has caused it to stop working to ensure your safety.

High Engineer only £150-250

Parts commonly replaced

  • PCB
  • Wiring harness
  • Safety sensor link

Related codes

107

Your boiler has lost communication with an external safety device, such as a smart control or external sensor, preventing it from operating correctly.

High Engineer only £120-250

Parts commonly replaced

  • External safety sensor
  • Wiring harness
  • PCB

Related codes

110

Your boiler has detected that the water inside the system has become too hot and has automatically shut down to prevent damage.

High Engineer only £150-300

Parts commonly replaced

  • NTC Sensor
  • Primary Heat Exchanger
  • Central Heating Pump

Related codes

118

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

High DIY-safe £0-£120

What to check first

  1. Locate the external filling loop, usually a silver braided hose with one or two valves underneath the boiler.
  2. Slowly open the valve(s) to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.
  3. Close the valve(s) firmly and ensure the boiler resets itself.

Parts commonly replaced

  • Filling loop
  • Pressure relief valve
  • Pressure sensor

Related codes

125

Your boiler is struggling to pump water around your heating system effectively, meaning it cannot properly heat your home or taps.

High Engineer only £150-350

Parts commonly replaced

  • Central heating pump
  • Diverter valve
  • System filter

Related codes

128

Your boiler has stopped because the flame inside it went out unexpectedly while it was trying to heat your home.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • PCB

Related codes

133

Your boiler is failing to light because it is not receiving enough gas or is unable to spark correctly to create a flame.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed circuit board

Related codes

134

Your boiler is failing to light because it cannot detect a flame, which means your heating and hot water have stopped working.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

135

Your boiler has stopped working because it cannot light its internal flame or is not receiving a consistent supply of gas.

High Engineer only £120-250

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Flame rectification probe

Related codes

160

Your boiler has detected a problem with the fan or its internal electronics, meaning it has safely shut itself down to prevent further issues.

High Engineer only £150-300

Parts commonly replaced

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

Related codes

321

Your boiler has detected an internal issue with one of its main sensors, meaning it cannot operate safely and has shut itself down.

High Engineer only £150-300

Parts commonly replaced

  • Flue gas sensor
  • NTC thermistor
  • Printed Circuit Board (PCB)

Related codes

384

Your boiler has detected an internal communication error and has safely shut itself down to prevent any further issues.

High Engineer only £120-250

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Wiring harness

Related codes

Bat

Your boiler's internal back-up battery for the safety monitoring system is low or failing and needs replacing.

Low Engineer only £70-130

Parts commonly replaced

  • Safety Assist battery pack

Related codes

4 operating states & engineer diagnostics

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

Avoid the next call-out bill

Monthly cover means no unexpected bills when your boiler breaks down.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.