My tankless water heater won't always light up. What's usually the problem?

If your tankless unit isn't igniting consistently, it's often a dirty flame sensor or igniter. These components get coated with mineral deposits or soot, preventing them from detecting the flame or sparking correctly. Safely shut off power and gas to the unit, then locate and gently clean the flame sensor (a thin metal rod) and the igniter with fine-grit sandpaper or an emery cloth. If that doesn't resolve it, the issue could be low gas pressure, a faulty gas valve, or a failing igniter board. Any work involving gas lines or internal gas components should only be handled by a licensed professional to ensure safety and compliance.