E04
Alpha
Air Pressure Switch / Draft Proving Failure
Display shows E04 and the unit will not fire; occurs immediately when a hot water tap is opened.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blocked intake or exhaust, Faulty air pressure switch, Cracked or disconnected pressure tubing, Condensate in pressure tubing
How to Fix / Troubleshooting
Safety: Turn OFF power and gas. Do not bypass safety switches.
- Inspect vent and intake: Check the Alpha intake and exhaust terminations for obstructions. Clear any debris, insect screens, or ice buildup.
- Check pressure tubing: Locate the air pressure switch on the combustion blower housing. Inspect the silicone tubing for cracks, kinks, or water. Drain any condensate and reattach firmly.
- Test switch operation: With power OFF, disconnect the wires from the pressure switch and check continuity with a multimeter while gently applying suction to the tubing port. The switch should change state. If it does not, the switch is likely defective.
- Reconnect and test: Reconnect all tubing and wiring, restore power, and run hot water. If E04 persists after clearing blockages, the air pressure switch may need replacement.
If you suspect vent design or installation issues, have an Alpha-certified technician evaluate the system.
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Repair Difficulty
Medium
3/5
Required Part
Air Pressure Switch
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