BoilerFaultCodesWorcester Bosch 78 Fault Code
The Worcester Bosch 78 fault code means: your boiler is having trouble creating the spark or flame needed to start up because the internal ignition components are out of alignment.. It appears on 1 Worcester Bosch model in our database.
Technical description: Electrode settings incorrect
What causes the Worcester Bosch 78 fault?
This fault occurs when the spark electrodes inside the boiler's burner move out of their precise position or become worn down over time. Without the correct spacing, the boiler cannot create a strong enough spark to ignite the fuel, or it may fail to detect that a flame has successfully started.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the 78 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 78 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