Why Is My Boiler Losing Pressure?

Boiler pressure dropping is one of the most common calls we take from homeowners in Tunbridge Wells and the surrounding area. In most cases the cause is straightforward, and a Gas Safe registered engineer can sort it quickly. Here’s what’s likely going on and what to do next.

What Should My Boiler Pressure Be?

Most combination boilers run comfortably between 1 and 1.5 bar when the heating is off. You can check this on the pressure gauge on the front of your boiler. If it’s sitting below 1 bar, or if it keeps dropping back down after you’ve topped it up, something in the system needs attention.

What Causes Boiler Pressure to Drop?

There are a few common reasons:

• A small leak somewhere in the system.

• A faulty or ageing expansion vessel.

• The pressure relief valve releasing water when it shouldn’t.

• Radiators that were recently bled, which removes water from the system.

• A boiler that’s worked hard over winter and is showing signs of wear.

A leak doesn’t have to be obvious. It might be a slow drip from a radiator valve, a joint in the pipework, or somewhere inside the boiler itself. If you can’t find a visible source and the pressure keeps dropping, that’s a job for an engineer.

If you notice the drop in summer, that's often simply because the heating has been off for a few weeks and there's been more time for a slow issue to become noticeable.

Can I Top Up the Pressure Myself? 

Yes, most modern boilers have a filling loop that lets you top up the pressure yourself. Your boiler manual will walk you through it, and it’s usually a matter of slowly opening a valve until the gauge reaches around 1.5 bar, then closing it again.

The important point is, if you’re topping up every few weeks, you’re managing a symptom and not fixing the problem. The pressure is dropping for a reason, and that reason won’t go away on its own.

When Should I Call an Engineer?

It’s worth getting a professional to take a look if:

• The pressure drops back down within a few days of topping up.

• You can’t find any obvious source of the leak.

• The boiler is making unusual noises alongside the pressure drop.

• The boiler is cutting out or showing a fault code.

• You’re not confident working on the system yourself.

Catching a small leak or a failing expansion vessel early is much cheaper than dealing with the consequences later. If your boiler is overdue a service, booking before the autumn rush means you'll get a prompt appointment and have peace of mind heading into winter. Our engineers cover Tunbridge Wells, Tonbridge, Sevenoaks and Crowborough.

What About Older Boilers?

If your boiler is more than ten years old and losing pressure regularly, it's likely that wear and age are behind the problem. Seals and internal components wear over time, and a boiler that needs constant attention is usually a boiler that’s approaching the end of its reliable life. An engineer can give you an honest assessment of whether repair or replacement makes more sense for your situation.

If your boiler is losing pressure and you’re not sure why, our Gas Safe registered engineers cover Tunbridge Wells, Tonbridge, Sevenoaks, Crowborough and the surrounding villages. We’re happy to take a look and give you a straight answer. Call us on 01892 535800 or visit our boiler repair and servicing page for more information.