Boiler Losing Pressure in Hexham - What It Means and What To Do About It

Published August 2026 | Boiler Losing Pressure

You've noticed the pressure gauge sitting lower than it should, or you keep topping up the boiler every few weeks and wondering why it keeps dropping. Should you just repressurise it again and get on with your day, or does a boiler that keeps losing pressure mean something more serious is going on?

This is the question our engineers hear from Hexham homeowners more than almost any other. The answer depends entirely on why your boiler is losing pressure - and that's what this guide is here to help you work out. There are two broad paths forward: topping up the pressure yourself, or getting a Gas Safe registered engineer in to find and fix the underlying cause. Knowing which one applies to your situation could save you a significant amount of money and a lot of cold evenings.

Option A - Repressurising the Boiler Yourself

Repressurising a boiler means adding water back into the sealed heating system to bring the pressure gauge back up to its normal operating range, which is typically between 1 and 1.5 bar when the system is cold. Most modern boilers - whether you've got a Worcester Bosch, a Viessmann, a Vaillant, or a Baxi - have a filling loop that lets you do this without any specialist tools.

How the process works

The filling loop is usually a short braided hose with one or two valves, connected between the cold mains supply and the heating system. You open the valve or valves slowly, watch the pressure gauge rise, and close them again when you reach around 1.2 bar. The whole thing takes about two minutes. Your boiler manual will show you exactly where to find the filling loop and how to use it safely. If you've misplaced the manual, the manufacturer's website will have a downloadable version.

Some newer boilers have an internal or built-in filling loop, which makes the process even simpler. A few Worcester Bosch models, for example, have a keyway filler that you operate with a small key rather than a hose. If you're not sure what type you have, our engineers suggest checking the model number on the boiler casing and searching for it online before you start.

Pros of repressurising yourself

• It costs nothing if you do it yourself
• It restores heating and hot water immediately
• It's safe to do on most modern sealed system boilers
• It works well for a one-off pressure drop, for example after a radiator bleed

Cons of repressurising yourself

• It only addresses the symptom, not the cause
• If the pressure drops again within days or weeks, you have a leak or a component fault somewhere
• Over-pressurising (going above 1.5 bar) can cause the pressure relief valve to discharge water, which some homeowners mistake for a new leak
• Doing it repeatedly without investigation can mask a worsening problem

Option B - Calling a Gas Safe Engineer to Diagnose the Cause

When a boiler keeps losing pressure, something in the sealed heating system is allowing water or air to escape. That something needs to be found and fixed. This is the work of a Gas Safe registered engineer, and in many cases it's not optional - certain repairs, particularly anything involving gas components, are legally required to be carried out by a registered professional.

The most common causes our engineers find when a Hexham boiler keeps losing pressure include:

• A leaking pressure relief valve (PRV) - this is a safety valve that opens to release pressure if the system over-pressurises, but can start weeping or dripping over time
• Pipework leaks, often hidden under floors or behind walls
• Leaking radiator valves or joints at radiator connections
• A faulty expansion vessel, which causes pressure to fluctuate and the PRV to open repeatedly
• Corrosion in older systems, particularly in properties across Northumberland with heating systems that haven't been power flushed in several years

What a diagnostic visit looks like

A Gas Safe engineer will typically start with a visual inspection - checking the boiler itself, the visible pipework, radiator valves, and the pressure relief valve discharge pipe outside the property. If no obvious leak is found, they'll often use a pressure test to isolate whether the loss is occurring in the boiler itself or in the wider heating circuit. Tools like the Voltrade GoFIX diagnostic system can flag common fault codes and help narrow down the location of the problem before physical checks begin, which saves time on the job.

The repair cost will depend on what's found. Replacing a faulty pressure relief valve typically costs between 100 and 200 pounds including parts and labour. Fixing a small pipework leak, if it's accessible, usually falls in the 100 to 250 pound range. If the expansion vessel needs recharging or replacing, expect to pay between 150 and 300 pounds. These are rough figures - the exact price will vary based on the boiler make, how accessible the fault is, and how much work is required.

Pros of getting an engineer in

• Identifies and fixes the actual cause rather than masking it
• Prevents the problem from getting worse or causing damage
• Legally required for any work involving gas components
• Gives you confidence the system is running safely
• Can often pick up other issues during the visit before they become expensive

Cons of getting an engineer in

• There's an upfront cost even if the fix turns out to be minor
• You'll need to wait for an appointment, though most local Hexham engineers can attend within a day or two for non-emergency faults
• In older boilers, a repair visit sometimes reveals additional underlying problems

Side-by-Side Comparison

Here's how the two approaches compare across the factors that matter most to homeowners:

Which Is Right for Your Situation

The single most useful question to ask yourself is this: how often is the pressure dropping?

If the pressure has dropped once and you can link it to a specific event - you bled your radiators last week, or someone adjusted a radiator valve - then topping it up yourself is a perfectly sensible first step. Bleeding radiators releases water along with the air, which causes a small pressure drop. One repressurise after a bleed is completely normal.

If the pressure drops again within two to four weeks, without any obvious explanation, that's when you need an engineer. A sealed heating system should hold its pressure for months or even years if everything is working correctly. Recurring pressure loss means water is escaping somewhere, and every time you top up without finding the leak, you're adding fresh, oxygenated water into the system. Over time, this accelerates internal corrosion and can shorten the life of your boiler significantly.

There's also a safety dimension worth mentioning. If you can see water dripping from the pressure relief valve discharge pipe - typically a copper pipe that exits through the external wall - don't ignore it. This is a sign that the system is over-pressurising at some point, often caused by a faulty expansion vessel. This isn't an emergency in the immediate sense, but it does mean the boiler's safety systems are working harder than they should be. An engineer should look at this promptly.

For homeowners in older Northumberland properties with ageing heating systems, our engineers often find that recurring pressure loss is a symptom of more widespread corrosion or a system that simply hasn't been maintained regularly. In these cases, a power flush alongside the repair can make a significant difference to how the system performs going forward.

What Hexham Homeowners Typically Choose and Why

In our experience, most Hexham homeowners try the repressurise route first - which is entirely sensible. It's quick, it costs nothing, and for a large proportion of one-off pressure drops, it works. The problem comes when they top up the pressure a second time, and a third time, without calling anyone in.

By the time an engineer arrives, the system has sometimes been repeatedly refilled over several months. In a few cases, this has caused corrosion damage inside the boiler that would have been avoided with an earlier diagnosis. A minor leak that costs 150 pounds to fix can end up contributing to a boiler replacement that costs 2,500 to 4,000 pounds if it's left long enough.

What we'd say to most Hexham homeowners is this: one repressurise is fine. Two in the same season means you need someone to look at it. Don't wait until the boiler locks out completely in the middle of a cold Northumberland winter to make that call.

We also hear from homeowners who were put off calling an engineer because they were worried about being told they needed a new boiler. In many cases, the actual repair is much more modest. A leaking radiator valve joint, for example, can often be tightened or re-sealed in under an hour. The Voltrade GoFIX diagnostic process is specifically designed to give you an accurate picture of what's wrong before any work starts, so there are no surprises on the invoice.

Making Your Decision

Has the pressure dropped more than once in the last six weeks?

If yes, this is the clearest sign that you need an engineer rather than another repressurise. A single drop can have a benign explanation - a recently bled radiator, a small air pocket working through the system. Two or more drops within a short period points to an active leak or a component fault that won't fix itself.

Can you see any visible signs of water around the boiler, pipework, or radiator valves?

Check around the base of the boiler casing, along any visible pipework runs, and at the valves either side of each radiator. Even a slow drip will leave limescale marks or slight discolouration on the floor or skirting board over time. If you spot anything like this, make a note of where it is and mention it when you book an engineer - it'll help them get to the fault faster.

Is your boiler more than ten years old?

Older boilers are more prone to pressure problems because seals, diaphragms, and expansion vessels degrade over time. If your boiler is ten years old or more and losing pressure regularly, it's worth asking the engineer for an honest assessment of its overall condition at the same time as the repair. This doesn't mean you'll need a replacement immediately, but it gives you the information to plan ahead rather than be caught out unexpectedly.

When did you last have the boiler serviced?

An annual boiler service by a Gas Safe registered engineer - which is a legal requirement in terms of who carries it out, not whether you do it - typically costs between 80 and 120 pounds and includes a pressure check as standard. If your boiler hasn't been serviced in the last two years, combining a service with a pressure investigation is often good value. The engineer will check the heat exchanger, burner, flue, and safety devices at the same time, which means any secondary issues get flagged before they develop into faults.

Frequently Asked Questions

How quickly will my boiler lose pressure if there's a leak?

It depends on the size of the leak. A very small drip from a radiator valve joint might cause the pressure to drop by 0.2 to 0.3 bar over a couple of weeks, which can be easy to miss. A larger leak from a failing pressure relief valve or a corroded pipe section can drop the pressure noticeably within days. If you check the gauge weekly and record the readings, you'll quickly get a sense of how fast the pressure is falling, which is useful information to pass on to an engineer.

Is it safe to keep repressurising the boiler while I wait for an engineer?

Topping up once to restore heating is fine in most cases. But repeatedly refilling a leaking system introduces fresh oxygenated water, which accelerates internal corrosion over time. If you're waiting more than a week or two for an engineer, try to repressurise only when the pressure drops below 0.5 bar and the boiler stops functioning. If pressure is dropping very rapidly - more than 0.5 bar per day - turn the boiler off and book an urgent appointment.

Do I need a Gas Safe registered engineer just to repressurise a boiler?

No - repressurising through the filling loop is not a gas operation and does not require a Gas Safe registered engineer. You can do this yourself using the boiler manual. However, any work that involves opening or repairing gas components, including replacing the pressure relief valve or working on the gas valve, must by law be carried out by a Gas Safe registered engineer. Always check that any engineer you hire is currently registered - you can verify this on the Gas Safe Register website using their licence number.

What pressure should my boiler be set at?

For most domestic sealed system boilers in the UK, the correct cold pressure is between 1 and 1.5 bar. Some manufacturers recommend 1.2 bar as an ideal starting point. When the system heats up, the pressure will naturally rise to around 1.8 to 2 bar - this is normal. If the pressure regularly climbs above 2.5 bar when hot, or if the pressure relief valve is discharging water, this suggests an expansion vessel problem rather than a simple pressure loss issue and needs professional attention.