Emergency

FA 306 on Worcester Bosch Greenstar 12i System

Your boiler has detected that the flame inside is not going out properly even after it has tried to shut the gas supply off.

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

What the manual says

Manufacturer manual

Ionisation detected after the gas valve closed.

From this model's manual

Verified against the Worcester Bosch/Worcester Bosch Greenstar 12i System installation & service manual.

Engineer required

This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

All 224 fault codes on the Greenstar 12i System

Seeing a different code? Every code this model can display, in one place.

8C 8E 9A 9A 362 9U 9U 233 112 113 114 115 200 201 202 203 204 205 207 208 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 227 228 229 230 231 232 233 234 237 238 239 240 241 256 257 258 259 260 261 261 EA 262 263 264 264 C1 265 266 266 CE 267 267 F0 268 269 269 EA 270 271 271 D4 272 272 F0 273 273 C4 274 276 276 E9 277 277 E9 278 278 F0 279 279 F0 280 280 F0 281 281 A1 282 282 H5 283 284 285 285 E9 286 286 D1 287 287 F0 288 288 CF 289 289 CF 290 290 F0 305 306 306 FA 307 308 309 310 311 312 313 314 315 316 316 E9 317 317 A3 318 318 E9 321 322 323 323 A8 324 325 326 327 328 329 332 333 338 341 342 343 344 345 346 347 348 349 350 351 353 354 357 358 359 364 365 372 373 374 375 376 380 800 808 810 828 A1 A1 281 A3 A7 A8 AC b1 b7 b7 257 Blue light Blue light on C1 C1 264 C4 C4 273 C6 C6 215 C7 C7 214 CE CF D1 D1 240 d3 D4 D4 271 E2 E2 222 E3 E4 E5 E5 218 E9 E9 219 E9 224 EA EA 227 EC ED EF EF 349 F0 F7 F7 228 FA FA 364 Fast flashing reset button Fb Fb 365 Fd FD 231 Flue overheat H5 H11 H13 i01 i02 LOCKOUT On / Off Reset Button Illuminated Slow flash (normally off)Slow flashing reset button

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