Furnace displays a water pressure fault, will not fire; pressure gauge shows low or zero.

Safety first: Turn off power before opening any internal panels. Do not work on a hot pressurized system.

• Check pressure gauge: Locate the system pressure gauge on the Roca furnace. Normal cold pressure is typically around 1.0–1.5 bar (check your manual). If below the minimum, the furnace will lock out.
• Top up system: Use the filling loop or built-in filling valve to slowly add water to the system until the gauge reaches the recommended pressure. Close the valve securely afterward.
• Bleed air: Bleed radiators and high points in the system to remove trapped air, then recheck and adjust pressure again.
• Inspect for leaks: Walk the system and look for damp patches, dripping valves, or corrosion marks on radiators, joints, and under the furnace. Repair any leaks before repeatedly topping up.
• Check pressure sensor connection: Inside the furnace, locate the pressure sensor or pressure switch tubing. Ensure the electrical connector is secure and any sensing tube is not kinked or blocked.

Warning: Do not overfill beyond the maximum indicated on the gauge. If pressure drops repeatedly, there is a leak or expansion vessel issue that should be evaluated by a professional.