Boiler Losing Pressure? What It Means and How to Fix It

If your boiler keeps losing pressure, you're not alone — it's one of the most common problems we get called to across Preston. Sometimes it's a two-minute fix you can do yourself. Sometimes it's a warning sign. Here's how to tell the difference.

What the pressure should be

Look at the gauge on the front of your boiler. Cold, it should read around 1 to 1.5 bar. Below 1 bar, most boilers lock out and stop heating. Much above 2.5–3 bar when hot and the system is over-pressurised.

Topping it up yourself

If the pressure has drifted down slowly over months, topping up is normal maintenance:

1. Turn the boiler off and let it cool.
2. Find the filling loop — usually a flexible silver hose with one or two small valves, underneath the boiler.
3. Open the valve(s) slowly and watch the gauge climb.
4. Close the valves at about 1.2 bar, then turn the boiler back on.

Your boiler's manual (or the manufacturer's website) has the exact steps for your model.

When dropping pressure means a fault

If you're topping up more than once every few months, the water is going somewhere. Usual suspects:

• A small leak on a radiator valve, joint or under the floor — look for damp patches or salty white crust on pipework.
• The expansion vessel has lost its charge — pressure shoots up when hot, then the relief valve dumps water outside.
• The pressure relief valve itself is passing — check if the overflow pipe outside drips.
• An internal fault like a failing heat exchanger — rarer, but it happens on older boilers.

None of these fix themselves, and repeated topping up with fresh water also feeds corrosion inside your system.

In Preston? We'll find it

We've been tracing leaks and fixing boilers across Preston for over 30 years — Gas Safe registered (reg. 203011), and honest about whether it's a repair or time for a replacement. Call 07949 075721 or send a message below for a free, no-obligation look.