Medium

5-A3 on Worcester Bosch Greenstar 2000

Your boiler is struggling to run at its lowest power setting, which can cause it to shut down for safety while heating your home or water.

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

What the manual says

Manufacturer manual

Minimum boiler output (heating and DHW).

Shared across the Greenstar 2000 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.

Engineer required

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

Find a Gas Safe engineer

Search the official register →

Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like 5-A3: no call-out fees, no surprise bills.

Approved partner

Domestic Appliance Guard

Unlimited call-outs, 24/7 helpline, no price-hike promise

Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

5-A1View →5-A2View →

All 235 fault codes on the Greenstar 2000

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

0-A1 0-A2 1-d4 4-A1 4-A2 4-A4 4-A5 4-A6 4-b1 4-b2 4-b3 4-b4 4-b5 4-b6 4-F1 4-F2 5-A1 5-A2 6-t1 6-t2 6-t3 6-t5 6-tA 6-tb 200 201 202 203 204 208 212 214 215 224 227 228 229 232 233 234 235 237 238 242 244 245 246 247 249 250 251 252 253 254 256 257 258 259 262 263 264 265 268 269 270 273 275 281 283 284 305 306 323 328 341 342 350 351 353 354 356 357 358 360 362 363 364 365 604 810 1010 1013 1014 1018 1019 1021 1021 B 1023 1023 R 1025 1025 -1027 1037 1037 W 1068 1068 W 1073 1073 W 1074 1074 W 1075 1075 W 1076 1076 W 2051 2051 -2085 2085 V 2908 2908 V 2909 2909 -2910 2910 V 2911 2911 V 2912 2912 V 2913 2913 -2914 2914 -2915 2915 V 2916 2916 V 2917 2917 V 2918 2918 -2920 2920 V 2921 2921 -2922 2922 -2923 2923 V 2924 2924 V 2925 2925 V 2926 2926 V 2927 2928 2928 -2930 2930 V 2931 2931 -2932 2932 -2940 2940 V 2941 2941 B 2942 2942 -2943 2943 -2945 2945 V 2946 2946 V 2947 2947 R 2948 2948 B 2949 2949 B 2950 2951 2951 V 2952 2952 V 2953 2953 B 2954 2954 B 2955 2955 B 2956 2956 O 2957 2957 V 2958 2958 V 2959 2959 B 2960 2960 B 2961 2961 V 2962 2962 V 2963 2963 B 2964 2965 2965 B 2966 2966 B 2967 2967 B 2971 2972 2973 2974 2981 3071 AC b1 C1 C4 C6 d1 d3 E2 EA LOCKOUT No LED Red - blinking Red - continuous

Related guides you might find useful

Banging, kettling or whistling noise

Each noise points to a different fault.

Boiler won't turn on: 9-step checklist

Work through these before the call-out.

Pilot light keeps going out

Older boilers: thermocouple, draught or gas supply.