BoilerFaultCodesWorcester Bosch T1 Fault Code
The Worcester Bosch T1 fault code means: your boiler is currently running a self-diagnostic check to ensure the ignition system is sparking correctly before it starts up.. It appears on 11 Worcester Bosch models in our database.
Technical description: Ignition test – checking the igniter spark
What causes the Worcester Bosch T1 fault?
This is a brief, automated check that occurs when the boiler prepares to light the burner. It happens because the system's control board needs to verify that the ignition electrodes are capable of creating a spark before releasing gas. It is not an indication of a breakdown, but rather a standard safety protocol being carried out by the internal computer.
DIY fix possible
Wait for the test to complete automaticallyIf the code stays on screen for more than a few minutes, try restarting the boiler via the Reset button
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Gas Safe Register →Worcester Bosch models that show the T1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch T1 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