Furnace frequently loses pressure, user must top up system often

Safety first: Allow system to cool before checking pressure components.

• 1. Inspect for visible leaks: Check all radiators, valves, and joints for signs of water. Repair any leaks found.
• 2. Safety valve check: Inspect the discharge pipe from the safety relief valve. If it is wet or dripping, the valve may be passing and need replacement.
• 3. Expansion vessel pre-charge: With system pressure at zero and isolated, measure the air charge at the expansion vessel Schrader valve. Recharge to the value specified by Junkers (often around 0.75–1.0 bar) using a hand pump.
• 4. Vessel integrity: If water comes out of the Schrader valve or the vessel will not hold pressure, the diaphragm is ruptured and the vessel must be replaced.
• 5. Monitor: After refilling and bleeding, monitor pressure over several days. Persistent loss with no visible leaks may indicate a hidden leak or heat exchanger issue requiring professional investigation.