How to Fix / Troubleshooting

Safety first: Isolate power. The fan and flue system are part of the combustion circuit; gas must be off when covers are removed.

Access the combustion fan and air pressure switch area.
Inspect the flue and air intake for obstructions such as leaves, nests, or ice. Clear any blockage from both the terminal and internal flue sections.
Check the silicone pressure tubes from the fan housing to the air pressure switch for splits, kinks, or disconnections. Replace damaged tubing.
Gently tap the air pressure switch body; if the fault becomes intermittent, the switch may be sticking and should be replaced.
Spin the fan impeller by hand (power off) to ensure it rotates freely and is not seized or noisy.
Restore power and reset the unit. If the fan does not run or the E3 persists, the fan motor or pressure switch likely requires replacement by a technician.

Furnace displays E3 and will not start the fan or ignition sequence

Possible Causes