A boiler that repeatedly loses pressure commonly has a leak in the heating circuit, a relief valve that is discharging, or an expansion-vessel problem. Topping it up every few days hides the symptom without correcting the cause.
Track when and how far the pressure falls
Check the gauge cold at roughly the same time over several days. A steady slow drop suggests water loss, while large swings between cold and hot can point toward expansion-vessel or pressure-control issues.
Look for visible leaks around radiators and pipes
Inspect valves, bleed points, joints, and damp marks without removing the boiler casing. Small leaks can evaporate from hot pipework and leave only corrosion or mineral staining behind.
Check the relief discharge pipe if accessible
A discharge pipe dripping outdoors may mean the pressure-relief valve has opened from excessive pressure or failed to reseal. Never cap that outlet; it is a safety device.
Recurring pressure loss needs service
If no accessible leak is found or pressure continues falling after one proper top-up, a technician should check the expansion vessel, relief valve, heat exchanger, and circuit. Do not open the boiler casing or work on gas components.
Sources
- U.S. Department of Energy — Home Heating Systems — Operation, controls, and general maintenance of home heating systems.