Boiler Losing Pressure Overnight
You top the system up, everything is fine, and by morning the gauge has sunk again..
You top the system up, everything is fine, and by morning the gauge has sunk again.
What is actually going on
You top the system up, everything is fine, and by morning the gauge has sunk again.
The realistic causes, in order
A small leak on buried pipework or a radiator tail, too slow to show as a visible puddle A relief valve passing quietly to the outside drain An internal boiler leak that evaporates off the hot heat exchanger before it ever drips
What we test on site
A pressure-drop test with the boiler isolated to separate appliance from system Thermal imaging or a careful visual trace along accessible pipework runs and under radiator valves The outside discharge pipe checked while the system is at working pressure
Get pressure that drops overnight diagnosed properly
Once located, most slow leaks are a valve gland, a compression joint or a vessel — all fixable without disruption.
Questions we get asked
What causes pressure that drops overnight on a gas boiler?
A small leak on buried pipework or a radiator tail, too slow to show as a visible puddle
What normally puts pressure that drops overnight right?
Once located, most slow leaks are a valve gland, a compression joint or a vessel — all fixable without disruption.
Is it safe to keep using the system with pressure that drops overnight?
Repeated topping up introduces fresh oxygenated water, which accelerates internal corrosion. It is a stop-gap, not a fix.