Keston Boiler Fault Codes

420 fault codes across 21 Keston boiler models — explained in plain English.

UK premium condensing boiler brand, now part of Baxi Group.

420 fault codes
21 models documented
6 currently sold
15 legacy models

Keston fault codes on this site

We document 420 fault codes across 21 Keston models, covering 205 distinct codes. Keston boilers use a mix of numbered codes and light or status indications. Codes for 20 of these models are taken directly from the manufacturer's own service or installation manual.

Models covered: C36, C55, Heat 45, Heat 55, System S30, Celsius 25, C36p, C40, C90 / C110, K170, K50, K60, K80, R-sm 20 FB, Combi 2, System 2 S30, C30 / C35, Qudos 28S, Combi C30, Combi 30, Combi2 C30, 30C, Keston 130.

Codes that appear on the most Keston models:
Ignition Lockout Overheat Lockout Flame Loss Fan Fault Outside Sensor Fault Low Water Pressure
Just want the most common Keston problems?
The top 8 faults across the whole Keston range — causes, DIY checks, repair costs.
Most serious

High-severity Keston fault codes

E 01
Your boiler is failing to light the flame needed to produce heat or hot water.
C36
 E02
Your boiler thinks a flame has started when it shouldn't have, usually caused by an electrical glitch or a faulty sensor signal.
C36
 E03
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
C36
 E07
Your boiler has shut down because the internal exhaust gases are getting too hot, which is usually caused by a circulation problem or a buildup of debris inside the main heating component.
C36
 E08
Your boiler is having trouble managing the flame and electrical signals, which is preventing it from heating your home safely.
C36
All models

21 Keston boiler models

C36
Combi Discontinued
29 fault codes · 2005 onwards
C55
Regular Discontinued
25 fault codes · 2002 onwards
Heat 45
Regular Discontinued
36 fault codes · 2013 onwards
Heat 55
Regular Discontinued
36 fault codes · 2013 onwards
System S30
System
20 fault codes · 2016 onwards
Celsius 25
System Discontinued
23 fault codes · 2006-2015
C36p
Combi Discontinued
29 fault codes · 2005 onwards
C40
Regular Discontinued
25 fault codes · 2002 onwards
C90 / C110
Combi Discontinued
26 fault codes
K170
System Discontinued
0 fault codes · 2013-2021
K50, K60, K80
System Discontinued
1 fault codes
R-sm 20 FB
Regular Discontinued
9 fault codes · 2002-2007
Combi 2
Combi Discontinued
7 fault codes · 2013-2018
System 2 S30
System
5 fault codes · 2022-present
C30 / C35
Combi
25 fault codes · 2015-present
Qudos 28S
System Discontinued
31 fault codes
Combi C30
Combi
25 fault codes · 2016 onwards
Combi 30
Combi Discontinued
14 fault codes · 2013 onwards
Combi2 C30
Combi
12 fault codes · 2022-present
30C
Combi Discontinued
31 fault codes · 2010 onwards
Keston 130
System
11 fault codes
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