BoilerFaultCodes 09
Possible faulty component
Baxi 636 COMBI Fault codes & diagnostics
19 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.
Combi Gas 2018-present
GC Number 47-077-30
Download the Baxi 636 COMBI manual
PDF
Versions & GC numbers
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. 19 Unrated
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 |
|---|---|---|
| 47-077-30 | 636 COMBI 36 | 2018–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 636 COMBI faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes
All 19 documented codes
Tap any card for details
15
Possible faulty component
20
Possible faulty component
28
Possible faulty component
40
Possible faulty component
100
Maximum output
109
Fault finding section J
110
Overheat of the primary system water
118
Primary water pressure is less than 0.5 bar
125
Primary water temperature has not changed by 1°C within 15-30 seconds of burner lighting OR primary water temperature actual temperature twice exceeds the selected temperature by 30° within 10 minutes (poor primary circulation)
128
Flame failure during normal operation
130
Flue/Sensor temperature test
133
Gas supply interrupted, ignition failed or flame not detected
134
Gas supply interrupted, ignition failed or flame not detected
135
Gas supply interrupted, ignition failed or flame not detected
160
Possible faulty component
304
Calibration Mode
321
Possible faulty component
384
Possible faulty component
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