Heat exchanger

The heat exchanger is a set of tubes or coils where heat moves into the water. In a gas heater, hot gas flows around the tubes. In a heat pump, it is called a condenser.

Bad chemistry hurts it. Low pH corrodes the metal. High pH and hard water leave scale that clogs the tubes. Both cut heat and flow. Keep your water balanced to protect it. A leaking or clogged exchanger usually means a costly repair, so a pro should confirm the cause.