F18 error; heater may not recognize remote thermostat or automation commands.

Safety first: Turn off power before working on low-voltage wiring.

• Identify remote sensor: If using a remote water or air sensor, locate the Nirvana remote temperature sensor connected to the low-voltage terminals.
• Inspect cable: Check the sensor cable run for cuts, splices, or damage. Ensure polarity (if required) is correct at both ends.
• Bypass test: Temporarily disconnect the remote sensor and configure the heater to use its internal sensor. If F18 clears, the remote sensor or wiring is faulty.
• Resistance check: Measure the remote sensor resistance and compare to spec. Replace if defective.
• Automation settings: Confirm that the heater is set to the correct control mode (remote vs local) in the setup menu.