Boiler shows error 91 and will not ignite; may be associated with low gas supply conditions.

Safety first: Turn off power and gas. Do not attempt repeated ignition if gas supply is suspect.

• Verify gas cock position: Ensure the isolation valve at the boiler is fully open.
• Check other gas appliances: If stoves or other heaters are weak or not working, contact your gas supplier to check supply pressure.
• Inspect gas line sizing (visual): Confirm that the gas pipe to the boiler appears appropriately sized and free of obvious damage or kinks.
• Professional testing: A technician should measure inlet and manifold pressures, clean or replace any gas filters, and test the gas valve operation.