Boiler shows error 19, may indicate expansion vessel or pressure-related fault during heating.

Safety: Allow the system to cool. Hot water under pressure can cause scalding.

• Observe pressure behaviour: Note the cold pressure and the pressure when the system is hot. If it rises above 3 bar and the relief valve discharges, the expansion vessel is likely faulty.
• Check for discharge: Look at the pressure relief valve discharge pipe outside. Dripping indicates overpressure or a passing valve.
• Engineer recharge: A technician can isolate and drain the boiler, then check and recharge the expansion vessel air side to the value specified by Biasi (often around 0.8–1.0 bar).
• Replace vessel if failed: If the diaphragm is ruptured, the expansion vessel must be replaced, and the system refilled and bled.