The display shows E12, and the heater will not start; this is often associated with an internal leak or condensation.

Safety: Turn off power and close the water supply immediately to prevent further damage and electrical hazards.

• Inspect for leaks: Remove the cover and carefully look for any signs of water, damp insulation, or corrosion. Check all compression fittings, unions, and the heat exchanger body.
• Dry the unit: If minor moisture is present, gently dry affected areas with a cloth. Allow the unit to air dry completely for several hours before re-energizing.
• Tighten fittings: Carefully tighten any slightly loose water connections. Do not overtighten plastic fittings.
• Check condensate sources: In humid environments, ensure the unit is not exposed to dripping pipes or other external moisture sources.
• Test and monitor: Restore water and check for leaks under pressure before turning power back on. If E12 returns or an internal component (like the heat exchanger) is cracked, discontinue use and have the unit inspected and repaired by a professional.