All Boiler Fault Codes

Every boiler fault code in our database — 1,442 codes across all UK manufacturers. Click any code to see which brands and models display it, with plain English explanations and fixes.

Most common fault codes

These appear on the largest number of boiler models across the UK market.

10 164 models 20 161 models 12 142 models F1 115 models 15 112 models 13 106 models 28 105 models 24 104 models F.10 102 models 06 96 models S.30 95 models S.53 95 models S.54 95 models F.28 94 models F.29 94 models F.62 94 models F.63 94 models F.67 94 models S.32 94 models S.34 94 models F.11 94 models F.22 92 models F.24 92 models F.65 92 models S.27 92 models F.64 91 models S.04 91 models S.20 91 models S.24 91 models F.61 90 models F.23 90 models F.27 90 models F.32 90 models F.13 90 models 40 88 models S.21 88 models S.23 88 models S.28 88 models S.31 88 models 14 87 models 05 87 models F.20 86 models S.01 86 models S.05 86 models S.07 86 models 30 85 models F.01 85 models S.02 84 models S.17 84 models 02 84 models

0-9 (469 codes)

-II- .0 00 000 0 (Flashing) 0 / A 0 0 0 4 0 8 0 bar 0.5bar 0A 01 001 0001 1 01 1 02 1 03 1 04 1 05 1 06 1 07 1 08 1 8 1 09 1 9 1 10 1 12 1 14 1 16 1 18 1 flash green 1 flash red 1 green flash 1 red flash 1 second ON 1 second OFF 1. 1.0 1.1 1.2 1.3 1.C 1A 1B 1C 1F 1P4 02 2 01 2 02 2 04 2 05 2 07 2 08 2 8 2 flashes 2 flashes green 2 flashes red 2 red flashes 2. 2.0 2.2 2.3 2.4 2.5 2.7bar 2.9 2.31 2.C 2/3/1 2A 2F 2H 03 3 003 3 01 3 02 3 03 3 04 3 05 3 06 3 07 3 bar 3 flashes 3 flashes green 3 flashes red 3 green flashes 3 red flashes 3.1 3.2 3.9 3/0/6 3A 04 004 4 07 4 17 4 flashes 4 flashes green 4 flashes red 4 green flashes 4 red flashes 4.1 4.2 4.3 4.4 4.5 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4# 4A 4C 4P 4Y 05 5 5 01 5 02 5 28 5 flashes 5 flashes green 5 flashes red 5 green flashes 5 red flashes 5.0 5.1 5.A 5A 06 6 6 10 6 flashes 6 flashes green 6 flashes red 6 green flashes 6 red flashes 6.1 6.2 6.3 6.5 6.A 6a 6C 07 7 7 01 7 02 7 03 7 04 7 05 7 06 7 07 7 22 7.1 7.2 7.3 7.4 7A 7C 7F 7L 08 8 8-9 8.1 8.2 8.3 8.4 8.6 8.79 8/2/5 08E 8E 09 9 9.1.37 9.3 9.4 9.5 9A 9C 9F 9L 9U 10 10, 11, 12, 13, 14 10.1 10.2 10E 11 12 13 14 15 16 016 17 18 19 20 20, 21, 22, 23, 24 21 21:0 22 23 23:0 24 25 26 27 28 29 29.30 30 030 30 40 50 60 70 80 31 031 32 33 34 35 36 36.0 37 38 39 40 41 42 43 44 46 47 48 49 50 50/70 51 52 53 54 55 56 57 58 58:0 59 60 060 61 62 63 65 67 68 69 70 71 72 73 74 75 76 77 78 79 80 80e 81 82 83 84 85 86 87 88 88°C flashing 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 121 122 125 126 127 128 129 130 131 132 133 134 135 140 146 151 154 158 160 162 164-026 169 169-083 170 171 180 183 200 201 202 203 204 205 210 214 215 216 217 218 220 226 229 / EA 231 232 234 / EA 235 241 242 250 254 257 260 263 265 267 268 270 272 273 276 277 280 281 284 285 286 287 289 290 290 F0 300 302 303 304 305 307 308 312 313 315 317 321 322 323 324 325 326 327 328 329 332 333 341 342 343 344 345 346 347 348 349 350 351 352 353 354 357 359 365 366 369 370 372 373 374 375 375 699 376 377 378 380 382 384 385 386 387 388 396 400 402 410 424 425 426 429 432 471 501 506 517 522 594 612 809 810 811 918 931 é45 布 & 皿 neons flashing 閃 neon illuminated

A (82 codes)

A A 01 A 03 A 10 A 37 A 39 A 40 A 41 A 77 A short pulse every 4 seconds A-4 A.5 A.12 A.18 A.19 A.20 A0 A1 A01 A02 A2 A03 A3 A04 A4 A5 A05 A06 A6 A7 A07 A8 A08 A09 A9 A10 A11 A12 A15 A16 A17 A18 A19 A20 A21 A23 A24 A30 A33 A40 A41 A42 A44 A61 A62 A63 A64 A70 A80 A98 A99 AF Air Flow Monitor AL 56 AL 82 AL 99 AL10 AL20 AL21 AL26 AL28 AL34 AL40 AL41 AL52 AL55 AL60 AL71 AL73 AL74 AL79 AM001

B (43 codes)

B b 18 b 19 b 24 b 25 b 26 b 28 b 29 b 30 b 65 B1 b4 b5 b7 B07 b7 257 B08 b18 Bat bb BC BCC Fault BE BLANK DISPLAY Boiler On Burner control box lockout light lit Burner indicator Flashing BURNER indicator Slow flash Burner lockout Burner On Burner On Neon Burner ON neon (green) Burner on neon NOT illuminated Burner reset light green/red alternate flash (0.5s) Burner reset light green/red fast flash (0.2s) Burner reset light orange steady Burner reset light orange/green alternate flash (0.5s) Burner reset light orange/green fast flash (0.2s) Burner reset light red fast flash (0.2s) Burner reset light red flash (0.5s) Burner reset light red steady Burner reset light red/green inverted flash (2.5s on, 0.5s off) Burner reset light red/orange inverted flash (2.5s on, 0.5s off)

C (25 codes)

C C0 C1 C1 10 C2 C3 C4 C5 C6 C7 C12 C13 C32 C33 C53 CA Casting Thermistor Fault CC CE CF CH PUMP panel LED flashing fast (2/sec) CO Communication fault Connection Cylinder Thermistor Fault

D (91 codes)

D d.00 d.01 D.1 d.02 d.04 d.05 d.06 d.07 d.08 d.09 d.10 d.11 D.13 D.14 D.15 d.16 D.17 D.18 d.19 D.20 d.21 D.22 d.23 D.24 d.25 D.27 D.28 d.31 d.33 d.34 d.35 d.36 d.39 d.40 d.41 d.43 D.44 d.45 D.47 d.50 D.51 d.58 d.60 d.61 d.62 d.64 d.65 d.66 d.67 d.68 d.69 d.70 d.71 d.73 d.75 D.77 d.80 d.81 d.82 d.83 D.84 d.85 d.88 D.90 D.91 D.93 d.94 d.95 D.96 D.128 D.129 D1 d2 D3 D4 D5 D6 d7 d8 d9 db dd DHW DHW PUMP indicator FLASHING DHW PUMP panel LED flashing fast (2/sec) DHW thermistor fault DHWsensor dP Dry-Fire dU

E (204 codes)

E 00 E 01 E 02 E 03 E 04 E 05 E 06 E 07 E 08 E 09 E 10 E 11 E 12 E 13 E 14 E 15 E 16 E 17 E 18 E 19 E 20 E 21 E 23 E 25 E 28 E 29 E 30 E 31 E 32 E 33 E 35 E 36 E 37 E 38 E 44 E 60 E 65 E 99 E.04.23 e/\/ E00 E0 E00-684 E00-688 E00.04 E01 E1 E01.12 E2 E02 E02-313 E02.15 E03 E3 E04 E4 E04.07 E04.23 E5 E05 E06 E6 E07 E7 E08 E8 E9 E09 E10 E11 E12 E012 E13 E14 E15 E16 E17 E18 E19 E20 E21 E22 E23 E24 E25 E26 E28 E29 E030 E30 E031 E31 E32 E33 E34 E35 E36 E37 E38 E39 E40 E41 E42 E43 E44 E45 E46 E48 E50 E52 E060 E62 E64 E65 E66 E72 E74 E77 E78 E79 E83 E83-013 E83-082 E83-086 E83-101 E83-122 E83-126 E83-127 E83-142 E83-145 E89 E92 E95 E96 E97 E98 E99 E108 E110 E118 E119 E125 E127 E128 E130 E131 E133 E160 E193 EA EC ED EE EF ER + 69 Er 01 Er 02 Er 03 Er 04 Er 05 Er 06 Er 07 Er 08 Er 09 Er 18 Er 19 Er 25 Er 99 Er.1 Er.2 Er.3 Er.4 Er.5 Er.6 Er.7 Er.8 Er.9 Er.10 Er.11 Er.12 Er.13 Er.14 Er.15 Er.16 Er.17 Er02 Er09 Err Err.5 Error 01 Error 04 Error 20 Error 28 Error 125 Error 130 ERROR CODE 1 ERROR CODE 2 ERROR CODE 3 ERROR CODE 4 ERROR CODE 5 ERROR CODE 6 Excessive temperature on primary circuit Explosive ignition Ext’ Interlock Off

F (203 codes)

F F 04 F 15 F 16 F.00 F.01 F.001 F.02 F.03 F.5 F.10 F.11 F.12 F.12 and F.91 F.13 F.14 F.17 F.20 F.22 F.23 F.24 F.25 F.26 F.27 F.28 F.29 F.32 F.33 F.42 F.43 F.46 F.49 F.52 F.53 F.54 F.56 F.57 F.61 F.62 F.63 F.64 F.65 F.67 F.68 F.70 F.71 F.72 F.072 F.73 F.74 F.75 F.76 F.77 F.78 F.80 F.81 F.83 F.84 F.85 F.085 F.86 F.87 F.88 F.89 F.91 F.92 F.93 F.94 F.97 F.338 F.342 F.359 F.381 F.401 F.456 F0 F00 F000 F0-237 F0C F1 F01 F1A F2 F02 F2 or Fn or Ln F3 F03 F4 F04 F4 OR L4 F5 F05 F5 OR L5 F5/F9 F6 F7 F07 F8 F08 F9 F09 F9 or L9 or F8 or L8 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32 F34 F35 F36 F37 F39 F40 F41 F42 F43 F47 F49 F50 F51 F52 F53 F61 F62 F63 F64 F65 F66 F67 F68 F70 F71 F72 F73 F74 F75 F76 F77 F81 F83 F84 F85 F86 FA False Flame Lockout FAN Fan does not run Fan Fault Fan Hunt FAN LOCKOUT Fan Purge Fan runs Fast flash Fault Fault on DHW sensor Faulty air pressure switch Faulty primary circuit FC FD FE FF FH FL Flame Flame detection error Flame Failure Flame Failure Neon flame lock-out Flame Loss Flame On Before Gas On Flame on before gas valve on FLASH FLASH ON Flash Off Flash FLASH OFF ON FLASH ON FLASH FLASH ON ON Flashing Red LED Flow return reversed Flow Thermistor Flow Thermistor Fault Flue overheat Fn FU FUSE

G (14 codes)

G G20 GREEN Green led flashing GREEN LED Flashing 8-times a second Green LED OFF, Red LED ON Green LED on GREEN LED ON every 0.5-secs GREEN LED ON every 6-secs Green LED ON, Red LED OFF GREEN LED Solid Green Light Green neon Green/Red - blinking

H (15 codes)

H H E H n H1 H03.05 H4 H5 H7 H8 H9 H9/L9 H21-052 Hb HE High Mains Voltage

I (14 codes)

I I.144 i1 i2 i3 i4 i6 i7 i14 Ignition failure Ignition fault Ignition lockout Internal fault IPX5D

J (2 codes)

J JP6

K (1 codes)

K

L (55 codes)

L L 01 L A L E L.095 L1 L01 L2 L3 L4 L4 or F4 L5 L5 or F5 L6 L7 L8 L9 LA/HA Lack of burner ignition LC LD3 LE LED 1 LED 1 Fast Flashing (8Hz) LED 1 Slow Flashing (2Hz) LED 2 LED 2 Fast Flashing (8Hz) LED 3 LED 4 LED 5 LED2 LED3 LF Lights: Flash, Flash, On Lights: Flash, Off, Flash Lights: Flash, Off, On Lights: Flash, On, Flash Lights: Flash, On, On Lights: Off, Off, Off Lights: On, Flash, Flash Lights: On, Off, Flash Lights: On, On, Flash Ln lock-out lock-out light lockout Lockout light Lockout light on Low mains voltage Low neon light Low system pressure low water pressure low-pressure LP Lt

M (5 codes)

M Main burner does not light main burner operating Mains LED flashing Mains LED off

N (45 codes)

N N.144 N.270 N.319 N/A n1 n2 n3 n4 n5 n6 n7 n8 n9 Neon 1 Neon 1 lit Neon 1 lit (NO) Neon 1 NOT lit Neon 2 Neon 2 lit Neon 2 lit (NO) Neon 2 NOT lit Neon 3 Neon 3 lit Neon 3 lit (NO) Neon 3 NOT lit Neon 4 Neon 4 lit Neon 4 lit (NO) Neon 4 NOT lit neon flashing neon flashing (Fan) neon flashing (Section E) neon flashing (Section H & K) neon flashing (Section I) neon flashing (Section J) Neon l1 Neon l2 Neon l3 Neon1 NO DISPLAY No light display when tap on No light indication No Water Flow No water flow lockout

O (17 codes)

OF OFF On / Off ON FLASH FLASH ON FLASH ON On Off Flash ON ON FLASH Orange LED flashing Orange LED on Orange Light OT ERROR Outside Sensor Fault Overheat Overheat condition OVERHEAT LOCKOUT Overheat Neon Overheat thermostat

P (42 codes)

P 0.9 P.00 P.01 P.1 P.02 P.03 P.04 P.4 P.05 P.06 P.07 P.12 p/-.- P1 P01 P2 P02 P3 P03 P04 P05 P06 P7 P07 P08 P10 P11 P12 P13 P21 P27 PCB Fault Pictogram of a spark Pilot does not light Pilot will not light Power On Power On Neon Pr00 Pressure of 3 or greater Pump Fault or Low Pressure Pump Overrun Pump runs

R (28 codes)

RED RED flashing (Reset button) Red flashing light Red LED RED LED BLINKS Red LED flashing Red LED illuminated Red LED On RED LED ON every 0.5-secs RED LED Solid Red LED: Flashing Red Red Light Red light (Egg timer symbol) Red light flashing (Lockout) Red neon Red reset button illuminated Reset Button Illuminated Reset LED is lit Reset light Reset light (illuminated) Reset Light / Overheat Reset neon Return Thermistor Return Thermistor Fault Return Thmr Fault Reverse polarity Room Stat Fault Running lamp flashing

S (67 codes)

S.0 S.00 S.01 S.02 S.03 S.04 S.05 S.06 S.07 S.08 S.10 S.11 S.13 S.14 S.15 S.16 S.17 S.20 S.21 S.021 S.22 S.23 S.24 S.25 S.26 S.27 S.28 S.29 S.30 S.31 S.32 S.33 S.34 S.36 S.37 S.39 S.40 S.41 S.42 S.46 S.53 S.54 S.58 S.59 S.76 S.88 S.91 S.92 S.95 S.96 S.97 S.98 S.99 S.108 S.109 Safety LOCK-OUT Safety Thermostat Safety thermostat activated SE Sensor Fault SENSOR STUCK LOCKOUT SF SH SL Slow flash Spare PCB Not Set STOP

T (11 codes)

t - T1/T2 t2 t6 t80 Tap symbol light ON TEC THERMISTOR Too many resets Too Many Restarts Two red lights flash rapidly

U (3 codes)

UF uP UU/tt

V (1 codes)

VF

W (3 codes)

Water pressure water pressure switch Water temperature low

Y (2 codes)

YELLOW LED ON every 0.5-secs YELLOW LED Solid

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026