Baxi 830 COMBI Fault codes & diagnostics

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

Combi Gas 2019-present
GC Number 47-077-39
Download the Baxi 830 COMBI manualThe official installation and service manual (PDF). 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 →

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
47-077-39 830 COMBI 2019–present

Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.

Just want the most common Baxi 830 COMBI faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 3 documented codes

Tap any card for details

15

Your boiler's main internal computer has developed a communication fault and is unable to run the system safely.

High Engineer only £250-£450

Parts commonly replaced

  • Main PCB (Printed Circuit Board)
  • Wiring Harness

Related codes

Full explanation for 15
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-£180

Parts commonly replaced

  • Flue NTC Sensor
  • Connecting wiring harness

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

  • Return NTC thermistor
  • Connecting wiring harness

Related codes

Full explanation for 40
Status & diagnostic codes

12 operating states & engineer diagnostics

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

1.0 Status Your boiler is currently performing an automatic internal check or initial setup process and is not experiencing an actual fault. 1.1 Diagnostic Your boiler has detected a general safety issue that requires the system to shut down to prevent potential damage or danger. 1.2 Diagnostic Your boiler has detected a communication error or a configuration issue that prevents it from starting safely. 2.1 Diagnostic Your boiler has detected a general internal fault that is preventing it from starting up correctly. 2.3 Diagnostic Your boiler is experiencing a communication error between its internal electronic parts, meaning it cannot safely operate or control its own functions. 2.5 Diagnostic Your boiler is struggling to ignite the flame reliably, which means the unit is currently preventing your heating and hot water from working to keep things safe. 3.1 Diagnostic Your boiler has detected an internal communication error and has safely shut down to prevent further issues. 7.5 Status Your boiler is experiencing a communication error between its internal electronic parts, meaning it has stopped working until the settings are correctly synchronised. 8.1 Diagnostic Your boiler has detected an internal issue with its electronic control system which is preventing it from operating correctly. 8.3 Status Your boiler has detected an issue with the sensor that monitors the water flow inside the system, preventing it from heating up correctly. 9.2 Diagnostic Your boiler has detected a general internal fault that prevents it from operating safely and needs a qualified professional to investigate. 20 Status Your boiler is currently in standby mode and is working exactly as it should.
Boiler cover options

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.