ATAG · iC, iS and iR range
504Flame lift
This code applies to iC Economiser, iC Combination, iS System, iR Regular. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Do not remove the boiler case or interfere with the flue.
- If the manual identifies a frozen external condensate pipe as a possible cause, follow only the manufacturer's external thawing instructions.
- Otherwise switch the boiler off and arrange a Gas Safe registered engineer.
How an engineer may fix it
Inspect the flue and air path, condensate system, burner, fan or Venturi, sensors and combustion readings; clear, repair, adjust or replace as the appliance instructions require.
Manufacturer source: ATAG — Boiler Troubleshooting (2019 & newer i-range). Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.