Safety first: Turn off power before removing any covers. Do not operate the boiler with venting disconnected.

Inspect venting: Go outside and check the intake and exhaust terminations for leaves, snow, bird nests, or debris. Clear any obstructions fully.
Check condensate drain: A clogged condensate trap or drain line can flood the inducer housing and affect the pressure switch. Inspect the trap and tubing for blockage and clean if necessary.
Inspect pressure tubing: Inside the boiler, locate the rubber or silicone tubing from the inducer housing to the pressure switch. Ensure it is not cracked, kinked, or disconnected. Replace damaged tubing.
Test operation: Restore power and call for heat. Listen for the inducer fan starting. If the fan does not run or E3 persists, the pressure switch or inducer motor may be defective.
Do not bypass the pressure switch: Bypassing safety devices is dangerous. If you suspect a bad switch or inducer, contact a qualified technician for testing and replacement.

Boiler shows E3 and will not start; fan may run briefly then stop

Possible Causes