Boiler pressure rises excessively during heating and may trigger the relief valve.

Safety: High pressure can cause leaks or component failure. Monitor the pressure gauge while troubleshooting.

• 1. Check cold pressure: When the system is cold, verify that pressure is within the recommended range (typically 12–15 psi for many systems).
• 2. Test expansion tank: With system pressure relieved, check the air charge in the expansion tank using a tire gauge. If no air or water comes out of the Schrader valve, the tank may be failed and should be replaced.
• 3. Inspect fill valve: Ensure the automatic fill valve is not stuck open and continuously adding water.
• 4. Professional diagnosis: If pressure still climbs rapidly, a technician should check for internal leaks in the Noritz boiler's heat exchanger and replace faulty components.