Water heater produces hot water but temperature fluctuates, alternating between very hot and lukewarm during a shower.

Safety: Risk of scalding. Set the DHW setpoint to a safe temperature (typically 120°F / 49°C) before troubleshooting.

• 1. Check DHW setpoint: Verify the DHW temperature setting on the Triangle Tube control. Avoid excessively high settings that can worsen fluctuations.
• 2. Verify stable flow: Ensure the shower or tap is fully open and that other fixtures are not rapidly opening/closing. Very low flow can cause the burner to cycle.
• 3. Inspect thermostatic mixing valve: If a mixing valve is installed on the hot outlet, check for sticking or scale. Exercise the valve by turning from hot to cold several times. Replace if it does not respond smoothly.
• 4. Plate heat exchanger scale: On combi units, a scaled DHW plate heat exchanger can cause rapid temperature swings. A technician can perform a chemical descaling using a pump and approved cleaner.
• 5. DHW sensor check: If the displayed DHW temperature jumps erratically, the DHW sensor may be faulty and should be tested and replaced.