356 High

Worcester Bosch 356 Fault Code

The Worcester Bosch 356 fault code means: your boiler is not receiving enough electrical power from the main supply to operate safely and has shut down as a precaution.. It appears on 17 Worcester Bosch models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Low mains voltage – the voltage may be interrupted or inconsistent and needs checking

What causes the Worcester Bosch 356 fault?

This fault occurs when the electrical supply entering the boiler drops below the minimum level required for the internal components to function correctly. The most common reason is an issue with the local power grid or a faulty internal circuit board that can no longer process the incoming voltage. In some cases, it can also be triggered by loose electrical connections or other high-drain appliances on the same circuit causing a temporary dip in power.

This fault can be more common during winter or extreme weather when the local power grid is under heavy strain, leading to 'brownouts' or fluctuating voltage levels.

Typical repair cost £100-350 (including labour)

Engineer required

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

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Worcester Bosch models that show the 356 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch 356 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026