John Wood water heater hot water temperature fluctuates significantly during a single shower

Safety: Sudden temperature changes can cause scalding. Adjust controls carefully.

• 1. Check for cross-connection: Shut off cold supply to the heater and open a hot tap. If water still flows strongly, there may be a plumbing cross-connection that must be corrected.
• 2. Inspect mixing valve: If a thermostatic mixing valve is installed on the outlet, adjust or replace it if it fails to maintain stable temperature.
• 3. Recirculation balance: Ensure recirculation return temperature and flow are properly balanced to avoid cold slugs.
• 4. Thermostat calibration: On electronic models, verify sensor placement and consider control replacement if overshoot is severe.