What does the Worcester Bosch A-b4 fault code mean?

Your boiler has detected an issue with the sensor that monitors the temperature of the hot water leaving the unit, which may result in inconsistent water temperatures.

How much does it cost to fix Worcester Bosch error code A-b4?

Typical repair cost for the Worcester Bosch A-b4 fault is £120-£220 including labour.

Worcester Bosch A-b4 Fault Code: What It Means & How to Fix It

What the manual says

Manufacturer manual

Hot water temperature: Outlet temperature

Shared across the Greenstar 8000 Life 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.

What causes this fault?

This fault occurs when the boiler's internal computer receives an implausible or missing signal from the sensor that monitors your hot water. The most common reason is that the sensor has developed an electrical fault or has become corroded, preventing it from accurately telling the boiler how hot the water is. In some cases, the issue may be caused by loose or damaged wiring connecting that sensor to the main control board.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Boiler cover options

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Related fault codes

A-b2View →

All 151 fault codes on the Greenstar 8000 Life Combi

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

1-A1 1-A2 1-A3 1-A5 1-A6 1-A7 1-b2 1-b3 1-b4 1-b7 1-b8 1-C1 1-C2 1-C4 1-C6 1-d1 1-d2 1-d3 1-d4 1-d5 1-E1 1-E2 1-E3 1-E4 1-EA 1-Eb 200 200 O 201 201 O 202 202 O 203 204 204 O 208 214 224 224 V 227 227 V 228 228 V 229 232 233 234 235 237 238 242 244 245 249 250 251 252 253 254 257 258 259 262 263 265 268 269 273 281 283 284 305 306 306 V 357 358 360 360 V 362 363 604 815 1010 1010 O 1013 1017 1017 W 1018 1019 1021 1021 B 1023 1025 1037 1037 W 1065 1065 B 1068 1068 W 1070 1071 1072 1075 1075 W 1076 1076 W 2085 2908 2910 2914 2915 2916 2920 2920 V 2923 2924 2925 2926 2928 2931 2940 2946 2946 V 2948 2948 B 2949 2950 2950 B 2951 2952 2955 2956 2957 2961 2962 2963 2963 B 2965 2965 B 2966 2966 B 2968 2969 2970 2970 B 2971 2971 B 2972 A-A5 A-b2

Your boiler has detected an issue with the sensor that monitors the temperature of the hot water leaving the unit, which may result in inconsistent water temperatures.

What the manual says

What causes this fault?

Engineer required

Avoid the next call-out bill

Related fault codes

All 151 fault codes on the Greenstar 8000 Life Combi

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