Low
9.C on Worcester Bosch Greenstar CDi Compact

Your boiler is displaying its current power level because a technician is likely testing the system or a specific testing mode has been left on.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Actual heat output (%)

Shared across the Greenstar range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This code appears when the boiler is placed into a manual testing mode, usually by a technician checking the system's performance. It indicates that the control board is temporarily overriding normal operation to run the burner at a fixed capacity. If you see this and no engineer is present, the testing dial on the front of the unit may have been moved or left in the wrong position.

DIY fix possible

Press the Reset button once to clear the displayEnsure the chimney sweep or service mode switch has not been accidentally activatedTurn the power off and back on at the fused spur if the code persists

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Related fault codes

9.AView →

All 365 fault codes on the Greenstar CDi Compact

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

1.A1.b1.C1.d1.E2.b2.C2.F3.b3.C3.E3.F4.F5.A5.b6.d6.E8.A8.b8.C8.E8.F8E9.A9.b9.d9.E9.F9U1012131415202130404243535456100101102103104117118119121122123124125126127128131132133170171200201202203204205207207 / CE208210210 / E9211212213213 / D4214214 / C7215215 / C6216216 / C6217217 / C7218218 / E5219219 / E9220220 / E9221221 / E9222222 / E2223223 / E2224224 / E9225227227 / EA228228 / F7229229 / EA230230 / EA231231 / FD232232 / D3233233 / 9U234234 / EA237237 / C4238238 / F0238 F0239239 / F0239 F0240240 / D1240 D1241241 / D1241 D1242256257257 / b7257 b7258259260261261 / EA261 EA262263264264 / C1264 C1265266266 / CE266 CE267267 / F0267 F0268269269 / EA269 EA270271271 / D4271 D4272272 / F0272 F0273273 / C4273 C4274276276 / E9276 E9277277 / E9277 E9278278 / F0278 F0279279 / F0279 F0280280 / F0280 F0281281 / A1281 A1282282 / H5282 H5283284285285 / E9285 E9286286 / D1286 D1287287 / F0287 F0288288 / CF288 CF289289 / CF289 CF290290 / F0290 F0305306306 / FA306 FA307308309310311312313314315316316 / E9316 E9317317 / A3317 A3318318 / E9318 E9321322323323 / A8323 A8324325326327328329329 / CE329 CE332332 / E5332 E5333338338 / F0338 F0341341 / D4341 D4342342 / D4342 D4343343 / ED343 ED344344 / ED344 ED345345 / EF345 EF346346 / EC346 EC347347 / E3347 E3348348 / EE348 EE349349 / EF349 EF350350 / E2350 E2351354357358359364364 / FA364 FA365365 / Fb365 Fb372373373 / 8C373 8C374374 / 8C374 8C375375 / E4375 E4376376 / E4376 E4380800800 / CC800 CC808808 / A7808 A7810828A1A1 281A7A8b1b7C1C1 264C4C4 273C6C7D1D1 240D4D4 271E2E5E9E9 219E9 224EAEA 227EFEF 349F0F0 237-239F0 263F7F7 228FAFA 306FA 364FbFb 365FdFD 231P1P2P3P4PCSEt1t2t3t4t6

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