🔥 Why Your Boiler Keeps Losing Pressure (and What You Can Do About It)

If your boiler pressure keeps dropping, you’re not alone  it’s one of the most common boiler issues we see at DM Emergency Plumbing. A drop in pressure can leave your heating system struggling to work properly, or worse, stop it completely.

Here’s what causes boiler pressure loss, and what you can safely do to fix it.

💧 What Is Boiler Pressure?

Boiler pressure is what keeps hot water moving around your central heating system. You can check it on the pressure gauge usually on the front of your boiler.

• Normal pressure: 1.0–2.0 bar (when cold).

• If it drops below 1 bar, you’ve likely got a pressure issue.

⚙️ Common Reasons Your Boiler Loses Pressure

1. A Leak in the System

Even a small leak in a radiator, pipe, or valve can cause a steady pressure drop. Check for damp patches, corrosion, or drips under the boiler. If you find one, turn off the water and call a professional  don’t attempt to fix boiler leaks yourself.

2. Radiator Bleeding

After bleeding your radiators, it’s normal for boiler pressure to drop a little because air has escaped from the system. Simply top it up using the filling loop (check your boiler manual for instructions).

3. Faulty Pressure Relief Valve (PRV)

The PRV releases excess pressure to keep your boiler safe. If it’s faulty or stuck open, it can cause water to escape, lowering the pressure. This is a job for a qualified engineer to inspect and replace if necessary.

4. Expansion Vessel Problems

The expansion vessel helps your boiler handle pressure changes as water heats up. If it fails, pressure can fluctuate or drop suddenly. This issue should always be diagnosed and repaired by a Gas Safe registered engineer.

5. Air in the System

Trapped air pockets can stop water circulating properly, making the pressure drop. Bleeding your radiators can sometimes fix this, but if it keeps happening, there might be a deeper system issue.

🧰 How to Repressurise Your Boiler (Safely)

If your boiler pressure is low but there’s no visible leak, you can repressurise it using the filling loop:

1. Turn off your boiler and let it cool.

2. Locate the filling loop (a silver, flexible hose under the boiler).

3. Open both valves slowly to let water into the system.

4. Watch the gauge stop when it reaches 1.5 bar.

5. Close both valves tightly.

If the pressure drops again soon after, it’s time to call a professional.

🚨 When to Call a Professional

If you’re topping up your boiler more than once a month, there’s likely a leak or faulty component.

At DM Emergency Plumbing, our engineers can quickly find the cause, repair it safely, and make sure your heating system runs efficiently all winter long.