Boiler displays E5, often with no heating or hot water and pump not running.

Safety first: Isolate electrical power and allow the boiler to cool. Water in the system may be hot and under pressure.

• Check system pressure: Ensure the pressure gauge reads around 1.0–1.5 bar. Low pressure can prevent the pump from running.
• Listen for pump operation: Restore power and call for heat. Place a hand on the pump body; if it hums but does not vibrate, it may be seized.
• Freeing a stuck pump (engineer level): A technician can remove the pump head and manually free the rotor, or replace the pump cartridge if worn.
• System cleaning: If sludge is suspected, the engineer should flush the system, clean filters, and consider adding inhibitor to protect the Worcester Bosch heat exchanger and pump.