Boiler displays E09 and shuts down, often accompanied by gurgling noises

Safety: Condensate is mildly acidic; wear gloves and eye protection when handling. Isolate power before removing the condensate trap.

• Check external condensate pipe: Look for kinks, sags, or freezing (white frost) on the plastic pipe leading outside. Thaw gently with warm water if frozen.
• Inspect trap (if accessible): On many Main condensing boilers, the condensate trap is a plastic assembly at the bottom. Place a tray underneath, remove the trap, and rinse it with clean water to remove sludge.
• Verify pipe slope: Ensure the condensate pipe runs with a continuous fall to the drain with no upward loops.
• Engineer checks:
  • Confirm correct trap assembly and seals to prevent flue gas escape.
  • Flush the heat exchanger condensate outlet to clear internal debris.
  • Modify or reroute external condensate pipework to comply with Main and building regulations (larger bore, shorter external run, insulation).