Furnace indicates expansion vessel or pressure fluctuation fault, pressure rises rapidly when heating

Safety first: Turn off power and allow the system to cool. Depressurize the system before checking the vessel.

• Check pressure behavior: Note cold and hot pressures. If cold is normal but hot pressure climbs to the relief valve opening, the expansion vessel may be faulty.
• Test pre-charge (for skilled users): Isolate the vessel from the system if possible and drain water from the vessel side. Use a tire gauge on the Schrader valve to measure air charge. Compare to Roca’s specified value (often around 0.8–1.0 bar). Repressurize with a pump if low.
• Inspect for water at Schrader valve: If water comes out of the air valve, the diaphragm is ruptured and the vessel must be replaced.
• Check connection pipe: Ensure the pipe between the vessel and system is not blocked with sludge.

Warning: Working with pressurized systems can be dangerous. If you are not experienced, have a heating professional service the expansion vessel.