Doncaster · BPHS
How to repressurise a boiler
Straight answer
Most combi boilers should read about 1.0 to 1.5 bar on the pressure gauge when the system is cold. If the needle is below 1 bar, the boiler may lock out. You can often top it up using the filling loop — two silver taps or a key under the boiler. Open them slowly until the gauge reaches 1.2 bar, then close them tightly. If pressure keeps falling, you have a leak: call a Gas Safe engineer.
How to top up boiler pressure
- Step 1. Make sure the boiler is cold or off. You want a cold reading, not a hot one.
- Step 2. Find the filling loop — usually a braided hose with two taps under the boiler, or a built-in filling point.
- Step 3. Open both taps (or the filling key) slowly. You should hear water entering.
- Step 4. Watch the gauge. Stop at about 1.2 bar (between 1.0 and 1.5).
- Step 5. Close both taps firmly. A leak from the filling loop means they are not shut.
- Step 6. Reset the boiler if it was locked out. If the pressure drops again within days, call us — do not keep filling.
When filling it up is not the fix
If you are doing this every week, the system is leaking. That is a repair, not a lifestyle. We find the leak, including ones that only show when the heating is on.
People also ask
What pressure should a boiler be?
Typically 1.0–1.5 bar when cold. Around 1.2 bar is a comfortable target. Over 2.5 bar is too high — do not keep filling. You may need to bleed a radiator or have a fault on the expansion vessel.
Why does my boiler lose pressure overnight?
A leak on a radiator, a weeping valve, a faulty pressure relief pipe dripping outside, or an internal heat exchanger leak. Repeated topping up hides the fault and can damage the boiler.
Is it safe to repressurise a boiler myself?
Yes, if you only use the filling loop as the manufacturer describes. Do not open the case. If you cannot find the loop, or water is leaking while you fill, stop and call us.