BoilerFaultCodesYour boiler has stopped working because it is not receiving the correct electrical supply, preventing the burner from igniting.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Burner blocked - Fault-supply voltage
What causes this fault?
This fault occurs when the boiler's internal control system detects an issue with the electrical power reaching the burner components. The most common reason is a failure in the ignition transformer or the main control board, which prevents the boiler from creating a spark to light the gas. It can also be triggered by loose internal wiring or fluctuations in your home's mains electricity supply.
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 for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like E4 — no call-out fees, no surprises.
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Viessmann Vitodens 333 is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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