Boiler frequently reaches high pressure and discharges water from relief valve

Safety: Hot water may discharge from the relief valve. Keep clear of the discharge pipe.

• Check cold pressure: When system is cool, note the pressure. If above recommended, drain some water from a drain valve to reduce to proper level.
• Test expansion tank: Tap the tank; if it sounds full of water or water comes from the air valve, the diaphragm has failed. Replace the tank.
• PRV check: If the automatic fill valve is overfeeding, it may need adjustment or replacement.
• Cross‑leak test: If pressure rises when DHW is used, the plate heat exchanger may be leaking between domestic and heating circuits and should be replaced.