Boiler runs then shuts down with error 16; unit feels very hot to the touch.

Safety: Allow the boiler to cool. Turn OFF power and close water and gas valves before removing covers.

• 1. Confirm adequate flow: Check that all isolation valves on the boiler supply and return are fully open. Verify that any system circulator pump is running when there is a call for heat.
• 2. Clean inlet filter: Shut off cold water to the boiler and remove the inlet water filter screen. Rinse out debris and reinstall.
• 3. Check strainers and mixing valves: Clean any Y-strainers or line filters in the boiler loop. Ensure thermostatic mixing valves are not stuck closed.
• 4. Descale heat exchanger: If the boiler has not been flushed in the last 12–24 months, perform a chemical descaling of the primary heat exchanger following Noritz procedures. This often resolves overheat issues caused by scale.
• 5. Inspect outlet thermistor: With power OFF, locate the outlet temperature sensor (thermistor) on the hot water outlet. Check for loose wiring or corrosion. Replace if damaged or out of specification (requires technician and meter).