Why Does Pressure Drop?
The only way a sealed central heating system loses pressure is if water escapes from it. This is a leak — it may be tiny (a weeping joint or valve packing) or more significant.
Common Leak Locations
- Radiator bleed valves (left slightly open)
- Radiator lockshield valve packing
- Pressure relief valve weeping (indicates overpressure)
- Expansion vessel (failed membrane causes pressure cycling)
- Buried or concealed pipework
What to Do
Repressionise to 1.5 bar and monitor. If pressure drops more than 0.5 bar per week, call an engineer to locate and repair the leak. A leak detection dye test can help find concealed leaks.
Sources: MCS certification and HSE.
