How to Read Your Boiler Pressure Gauge
The pressure gauge on a sealed system boiler is one of the simplest diagnostic tools in your house, and most homeowners can read it safely without touching anything else..
The pressure gauge on a sealed system boiler is one of the simplest diagnostic tools in your house, and most homeowners can read it safely without touching anything else.
What the numbers mean
Most systems run correctly between 1 and 1.5 bar when cold. The gauge often has a coloured band marking the normal range.
Reading it correctly
Check when the heating is cold, not mid-cycle, since pressure rises slightly as the system heats up.
What a reading tells you
Low pressure usually means a slow leak or a recent bleed of radiators; consistently rising pressure points to the expansion vessel or filling loop.
Questions we get asked
Can I top up the pressure myself?
On many systems yes, using the filling loop as per the boiler manual, but if it keeps dropping the cause needs finding, not just topping up.
What if the pressure is too high?
Slightly high pressure after filling can be released via a radiator bleed valve; persistently high pressure needs an engineer to check the expansion vessel.
Is a pressure problem dangerous?
It's rarely an immediate hazard, but low pressure can trip the boiler off and high pressure can strain seals over time.