Understanding Boiler Pressure: A Guide for Croydon Residents

by Peter Harker | Apr 24, 2025

As someone who works on heating systems across Croydon every day, one of the most common issues I’m asked about is boiler pressure. It’s something that can cause big problems if ignored, yet most people don’t realise how easy it is to monitor and maintain, until something goes wrong!

In this guide, I’ll explain what boiler pressure is, why it matters, how to check and top it up, and what to do if your system keeps losing pressure. Whether you live in a family house in South Croydon or a top-floor flat in Norbury, this post is designed to help you better understand your heating system — and avoid costly callouts.

What Is Boiler Pressure?

Boiler pressure refers to the pressure of the hot water that runs through your central heating system. It’s different from your water pressure, which affects taps and showers. This internal pressure helps move hot water through your radiators and pipework efficiently. If the pressure is too low, your boiler may not function properly. If it’s too high, it could damage parts of the system or cause leaks.

What’s the Correct Boiler Pressure?

Most UK boilers operate best when the pressure is between 1.0 and 1.5 bar when the system is cold. This might rise slightly when the boiler is on and water is being heated — but it should never exceed 2.5-3.0 bar.

You can usually check the pressure using the pressure gauge on the front of your boiler. Some modern digital models may show a numerical reading, while others use a simple dial with green (safe) and red (too low/high) zones.

Why Is Boiler Pressure Important?

Maintaining the right boiler pressure is essential for several reasons:

Efficiency: The right pressure helps your boiler and radiators work more efficiently, heating your home evenly.
Reliability: Low pressure can cause your boiler to shut down completely, leaving you without heat or hot water.
Safety: Excessive pressure can cause system strain, leaks or even damage components such as the pressure relief valve.

Signs of Low Boiler Pressure

In Croydon, I often visit homes where the boiler has stopped working simply because the pressure is too low. If you notice any of the following, it might be time to check your pressure:

Radiators aren’t heating up properly
Your hot water is lukewarm or inconsistent
The boiler keeps switching off or showing an error code
The pressure gauge reads below 1.0 bar

What Causes Boiler Pressure to Drop?

Pressure loss is very common and usually nothing to panic about, especially if it happens slowly over time. Here are a few reasons why it might be happening:

Bleeding Radiators: This releases trapped air but can also release some pressure.
Minor Leaks: Small leaks from valves, radiators or pipe joints can cause gradual pressure loss.
Expansion Vessel Issues: If the internal air pressure in the expansion vessel drops, it can affect the overall system pressure.
Old Components: Ageing seals and valves are more prone to letting pressure escape.

If you’re frequently topping up your boiler, it could indicate a leak or another issue that needs professional attention. You can book a boiler repair with us here.

How to Top Up Your Boiler Pressure

If your boiler pressure is too low, you can often top it up yourself using the filling loop — usually found underneath the boiler. Here’s how to do it safely:

Turn off your heating and let the boiler cool.
Locate the filling loop (a flexible silver or braided hose).
Open both valves slowly until you hear water flowing.
Watch the pressure gauge rise to around 1.3-1.5 bar.
Close the valves and turn the boiler back on.

Be sure to check your boiler manual or manufacturer’s guidance. If you’re unsure or the pressure drops again soon after topping up, it’s time to call in a qualified engineer.

Can Boiler Pressure Be Too High?

Yes — and it can be just as problematic as low pressure. High pressure usually means there’s too much water in the system or a component like the expansion vessel isn’t functioning correctly.

If your pressure regularly goes above 2.5-3.0 bar, or you notice water discharging from the external overflow pipe, contact a professional. High pressure can lead to long-term damage if left unchecked.

What If My Boiler Keeps Losing Pressure?

Pressure that drops regularly or immediately after topping up could indicate:

A hidden leak in the pipework or radiators
A faulty pressure relief valve (PRV)
Problems with the expansion vessel

This is something I see quite often in older Croydon properties where the heating system hasn’t been upgraded or maintained recently. If your boiler is under pressure, literally, we’re happy to take a look. Book a local boiler repair here.

Why Regular Servicing Helps Maintain Boiler Pressure

As part of our annual boiler servicing in Croydon, we always check and balance boiler pressure, inspect the expansion vessel, and test safety valves. These steps help ensure your system maintains consistent pressure throughout the year.

By servicing your boiler once a year, you can:

Prevent breakdowns caused by pressure loss or component failure
Spot and fix minor leaks before they cause major issues
Improve energy efficiency and heating performance
Protect your boiler’s warranty (which often requires annual servicing)

Boiler Pressure & Safety: Don’t Take Risks

Working with gas appliances or trying to fix pressure problems without proper training can be dangerous. If you’re unsure, it’s always better to call a professional.

Gas Safe engineers like ourselves are trained to safely work on boilers and pressure systems. We’ll identify the root cause of any issue and provide a clear, honest solution, no guesswork, no unnecessary parts.

Real-Life Example from a Croydon Home

Not long ago, I helped a family in Shirley whose boiler kept losing pressure. They’d been topping it up every week for over a year, not realising the expansion vessel had failed. This caused strain on the system and eventually cracked a valve. A simple £60 fix had now turned into a £300 repair — all because the pressure issue went unchecked for too long.

Since then, we’ve been servicing their boiler annually, and they’ve had no issues since. It’s a perfect example of why early action matters.

Frequently Asked Boiler Pressure Questions

Is it normal for boiler pressure to rise when heating is on?

Yes — a slight increase is perfectly normal. If it jumps dramatically or exceeds 3.0 bar, you may have a system fault.

How often should I check my boiler pressure?

It’s good practice to check it once a month, especially during winter when the boiler is in regular use.

Can I fix boiler pressure issues myself?

You can safely top up the system using the filling loop. But if pressure drops frequently or won’t rise at all, it’s time to get it checked by an engineer.

Boiler pressure might seem like a small thing, but it plays a big role in keeping your heating system running smoothly. Whether your pressure is too high, too low, or fluctuating regularly, understanding what it means, and how to respond, can save you stress, discomfort, and a whole lot of money.

If you’re in the Croydon area and struggling with your boiler pressure, or you just want the peace of mind of a properly serviced system, we’re here to help. Our team is friendly, experienced, and ready to keep your heating system in top condition.