Blockage High

Main Blockage Fault Code

Also written as BLOCKAGE — same fault.

The Main Blockage fault code means: your boiler has sensed it is getting too hot too quickly and has shut down to prevent damage, usually because water isn't moving through the system properly.. It appears on 1 Main model 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: Temperature protection
Typical repair cost £120-350 (including labour)

DIY fix possible

Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barPress the Reset button for five secondsListen for any unusual banging or gurgling noises

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Main models that show the Blockage fault code

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

Source

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

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026