What does the Worcester Bosch 811 fault code mean?

Your boiler has failed to reach the high temperature required to kill potential bacteria in your hot water supply, so it is alerting you that the water may not be safe for certain uses.

How much does it cost to fix Worcester Bosch error code 811?

Typical repair cost for the Worcester Bosch 811 fault is £120-250 including labour.

Worcester Bosch 811 Fault Code: What It Means & How to Fix It

What the manual says

Manufacturer manual

Hot water heating: thermal disinfection failed

Shared across the Greenstar 4000 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 811: 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.

All 105 fault codes on the Greenstar 4000 System

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

200 201 202 203 204 208 214 224 227 228 232 233 234 235 237 238 242 245 249 250 251 252 253 254 258 259 262 263 265 268 269 273 281 283 284 305 306 353 357 358 360 362 363 810 1010 1013 1017 1018 1019 1021 1022 1023 1037 1065 1068 1070 1071 1072 1073 1074 1075 1076 2085 2908 2910 2914 2915 2916 2920 2923 2927 2928 2931 2940 2946 2948 2949 2950 2951 2951 V 2952 2952 V 2957 2957 V 2961 2961 V 2962 2962 V 2963 2963 B 2964 2964 B 2965 2965 B 2966 2966 B 2967 2967 B 2970 2970 B 2971 2971 B 2972 2972 V

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on a combi.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

Your boiler has failed to reach the high temperature required to kill potential bacteria in your hot water supply, so it is alerting you that the water may not be safe for certain uses.

What the manual says

Engineer required

Avoid the next call-out bill

All 105 fault codes on the Greenstar 4000 System

Related guides you might find useful

No hot water but heating works

Is boiler cover worth it?

When to replace your boiler

Recently viewed