Heater’s flow switch rattles or chatters audibly during operation.

Safety first: Turn off pump and power before modifying plumbing or valves.

• Straighten pipe runs: Ensure there is a straight length of pipe before the heater as recommended by Elecro to reduce turbulence.
• Adjust valves: Open upstream valves fully and adjust bypass valves to provide steady flow through the heater.
• Check pump speed: On variable-speed pumps, adjust speed to maintain stable flow above the flow switch threshold.

Persistent chattering can wear out the flow switch; stabilizing flow will extend its life.