A sealed heating system should hold its pressure for months. If yours drops every week, water is leaving the system somewhere, and topping it up is treating the symptom.

This page covers both losing pressure repeatedly and pressure that is simply too low right now.

What the pressure should be

Between 1 and 1.5 bar when the heating is cold. It rises a little as the system heats up, which is normal. Below about 0.5 bar most boilers lock out.

Topping it up, which is the easy part

1. Turn the boiler off and let it cool.
2. Find the filling loop, usually a braided silver hose under the boiler with a valve at each end.
3. Open both valves slowly until the gauge reads 1.5 bar.
4. Close both valves.
5. Turn the boiler on and press reset.

Why you should not keep doing it

Where the water actually goes

• A radiator valve weeping. Look for staining or a small green or white deposit at the valve.
• The pressure relief valve discharging. There is a copper pipe through an outside wall near the boiler. If it is wet or dripping, that is where your pressure is going, and it usually means a failed expansion vessel.
• Buried pipework. Under floors or in walls, and this is the one people never find on their own.
• A failed expansion vessel. Inside the boiler. Common, and it is a repair rather than a replacement boiler.
• The boiler heat exchanger. Less common and more serious.

How a hidden leak is found

Without lifting your floors. Thermal imaging shows a heating leak as a plume of warmth. Acoustic equipment picks up the sound of water escaping under pressure. Tracer gas finds what neither of those can. See leak detection, and if you are claiming on insurance, trace and access.

How Vantage can help

We hold specialist leak detection equipment, we are Gas Safe registered, and we cover Hertfordshire, Bedfordshire and Cambridgeshire.

Frequently asked questions

How often should I top up boiler pressure?

Once or twice a year is normal. Weekly means a leak.

Is losing pressure dangerous?

Not in itself. The boiler locks out to protect the heat exchanger. The damage is gradual, through corrosion.

What if I cannot see any leak?

Most are hidden under floors or inside the boiler. That is what leak detection equipment is for.

Does insurance cover it?

Most buildings policies cover trace and access. Check your wording and notify before work starts.

Want it sorted properly?

Anything past the free checks above needs a Gas Safe engineer with the right test kit. Ring Vantage on 01462 506374, any hour, any day of the year. You will get an honest arrival time rather than a comforting one, and the price before the work.