Richmond tankless water heater provides hot water for a short time, then turns cold, then hot again (temperature fluctuation).

Safety first: Risk of scalding due to temperature swings—warn users.

• Check for crossover: Shut off cold supply to the heater and open a hot tap. If water still flows strongly, there is a crossover (e.g., failed single-handle faucet cartridge) that must be repaired.
• Descale heat exchanger: Perform a full descaling to restore proper heat transfer and temperature control.
• Verify minimum flow: Ensure fixtures provide enough flow to keep the heater running steadily.
• Inspect temperature sensors: Check wiring and operation of inlet and outlet temperature sensors; replace if faulty.