E18
Atlantic
Control Transformer / Low-Voltage Power Fault
Furnace displays E18, no response to thermostat, sometimes after lightning or power surge.
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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
Blown control transformer, Shorted 24 V circuit, Loose primary wiring to transformer, Overcurrent from external devices (humidifier, zone valves)
How to Fix / Troubleshooting
Safety: Turn off power at the breaker. This repair involves mains voltage and should be done by a qualified person.
Steps:
- Check low-voltage fuse: Inspect and replace the low-voltage fuse on the Atlantic control board if blown. If it blows again immediately, there is a short.
- Measure transformer output: With power on (qualified person only), measure the secondary voltage of the transformer. It should match the rated 24 V (or model-specific) output. If there is no output, the transformer is likely failed.
- Inspect connected devices: Disconnect external 24 V loads (humidifier, air cleaner, zone controls) and retest. A short in an accessory can damage the transformer.
- Replace transformer: Install a replacement with the same voltage and VA rating approved by Atlantic.
Note: Always correct the cause of the short before installing a new transformer.
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Repair Difficulty
Professional Required
5/5
Required Part
Control Transformer
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