System pressure rises rapidly when heating and relief valve discharges water

Safety first: Hot water may discharge from the safety valve. Allow system to cool before working on pressure components.

• Check cold pressure: Note the system pressure when cold. If already high (>1.8 bar), drain some water to reduce to about 1.2 bar.
• Observe pressure rise: Run heating and watch the gauge. If it climbs close to 3 bar and the relief valve opens, suspect the expansion vessel.
• Recharge vessel (technician): A technician can isolate the vessel, drain system pressure, and recharge the air side to the specified value using a pump and gauge.
• Replace vessel: If the vessel will not hold charge or the diaphragm is ruptured, replace the expansion vessel.
• Check relief valve: After repeated discharges, the safety valve may not reseal properly and may also need replacement.