Hot water runs hot then quickly goes lukewarm or cold during a shower

Safety: Water temperature may fluctuate; warn users before testing.

• 1. Check recirculation: If the system has a DHW recirculation loop, verify that the ACV recirculation pump is running and that check valves are correctly installed.
• 2. Piping inspection: Look for cross-connections between cold and hot lines (e.g., faulty single-lever mixers) that can cause cold water to backfeed.
• 3. Plate exchanger cleaning: On indirect ACV units with a plate heat exchanger, descale or replace the exchanger if temperature drops under sustained flow.
• 4. Control settings: Ensure anti-legionella cycles or eco modes are not limiting available hot water during peak use.

If the problem persists, a hydraulic review of the installation by a heating engineer is recommended.