Boiler losing pressure? What to check before you call

A boiler that keeps losing pressure is one of the most common calls we get. Here’s what’s normal, what you can safely check yourself, and when it’s time to call an engineer.

Most modern boilers have a pressure gauge on the front or a pressure reading on the display. If the pressure drops too low, the boiler will usually stop working and show a fault code to protect itself.

What pressure should my boiler be?

For most combi and system boilers, the pressure should sit at around 1 to 1.5 bar when the heating is cold. It’s normal for it to rise a little when the heating is on. Your boiler manual will tell you the exact range for your model.

Things you can safely check yourself

• Look for leaks. Check around radiators, radiator valves, towel rails and the pipework under the boiler for drips, damp patches or stains.
• Have you bled your radiators? Bleeding radiators lets out air and water, which lowers the pressure. You may just need to top it up afterwards.
• Check the pipe outside. Many boilers have a small copper pipe running through the wall to the outside. If it’s dripping, the pressure relief valve may be letting water out.
• Top up the pressure. Many boilers have a filling loop or key. Only do this if your boiler manual shows you how – and don’t overfill it.

When to call an engineer

If you have to top up the pressure more than once every few weeks, something is wrong. The usual causes are:

• A small leak somewhere on the system – sometimes hidden under floors
• A faulty pressure relief valve
• An expansion vessel inside the boiler that has lost its charge

The last two are parts inside the boiler, so they need a Gas Safe registered engineer. Topping up over and over can also bring in fresh water and air, which speeds up corrosion inside your system.

How we can help

Our diagnostic visit is £78 inc VAT, and it comes off your bill if you go ahead with the repair on the day. We check the boiler and the rest of your system, explain what we find in plain English and give you a fixed price before any work starts. BoilerJax members pay no call-out or diagnostic charges.

Need a hand?

Call or WhatsApp us on 01256 436 001 – a real person will help.

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