Boiler starts but shuts down after a few seconds without showing a code

Safety: Repeated failed starts can flood the combustion chamber with gas. If you suspect gas buildup, shut off gas and call a professional.

• Observe sequence: Watch the boiler through the inspection window. Note whether the flame appears and then goes out, or if it never lights.
• Check safety chain: Inspect wiring to high limit, low water cutoff (if present), and pressure switches. Reseat connectors.
• Clean flame sensor: A weak flame signal can cause early shutdown. Clean the Dettson flame sensor as described in earlier steps.
• Professional testing: If the issue persists, a technician should monitor flame current, gas pressure, and safety switch operation.