Boiler Losing Pressure in Pulborough - What It Means and What to Do

Published August 2026 | Boiler Repair

A homeowner in Pulborough notices something's off on a cold Tuesday morning in January. The radiators in the bedrooms are barely warm, even though the thermostat is set to the usual temperature. She heads to the boiler cupboard under the stairs, glances at the pressure gauge on the front of her Worcester Bosch combi, and sees the needle sitting just below the 0.5 bar mark - well below the green zone. She tops it up using the filling loop, the boiler fires again, and the house warms up. But two days later, the same thing happens. This time, she calls an engineer.

What Was Actually Going On

Boiler pressure loss is one of the most common calls our engineers receive across West Sussex. The pressure gauge on a sealed central heating system should typically sit between 1 and 1.5 bar when the system is cold, rising slightly to around 2 bar when the heating is running. When that needle keeps dropping - especially if it happens repeatedly after you've topped up the system - something is wrong beyond simple user error.

In this Pulborough homeowner's case, our engineer arrived and ran the Voltrade GoFIX diagnostic check, which helps identify whether the pressure loss is linked to the boiler itself or the wider heating circuit. The results pointed to a gradual leak rather than an internal boiler fault, which narrowed things down considerably.

There are several common causes of a boiler losing pressure, and understanding them helps you know what kind of fix you're dealing with:

A Leak Somewhere in the System

Even a very small drip from a pipe joint, a radiator valve, or a connection behind the boiler can cause pressure to fall over hours or days. These leaks are sometimes too small to leave a visible puddle, but over time they allow water to escape from the sealed system. In this case, our engineer found a slow weep from a compression fitting on the pipework behind the boiler - typical of a joint that had been under repeated thermal stress over several winters.

A Faulty or Weeping Pressure Relief Valve

The pressure relief valve (PRV) is a safety device that releases water if the system pressure climbs too high. When a PRV starts to fail, it can weep water slowly even when the pressure is normal. You might notice a small amount of water or limescale residue around the discharge pipe outside the house. This is often mistaken for condensate from the flue rather than a valve issue.

A Failing Expansion Vessel

Inside every sealed heating system, there's an expansion vessel - a small tank, usually grey or red, that accommodates the water as it expands when heated. Over time, the rubber diaphragm inside this vessel can degrade or lose its charge of pressurised air. When this happens, the system can't handle the expansion properly. Pressure may spike when the heating comes on, then drop when it cools. It's a classic cycle that many Pulborough homeowners describe as "it keeps going low but then it's fine for a bit."

Air in the System After Bleeding

If you've recently bled your radiators - which is worth doing every autumn - you will have released some water along with the trapped air. This is expected and normal, and it's why you top up the pressure after bleeding. If the pressure then stays stable for weeks, bleeding was likely the cause. If it keeps dropping, something else is going on.

How the Problem Was Resolved

Once our engineer identified the weeping compression joint behind the boiler in Pulborough, the repair itself was not complicated. The system had to be partially drained to isolate that section of pipework safely. The compression fitting was dismantled, the olive (a small copper ring that forms the seal) was replaced, and the joint was remade. This is exactly the kind of repair that requires a Gas Safe registered engineer when it involves work close to the boiler itself, even if the joint in question is on the water side rather than the gas side - you want someone who knows what they're doing working inside a boiler cupboard.

Gas Safe registration is a legal requirement in the UK for any work on gas appliances. If an engineer can't show you their Gas Safe ID card when asked, don't let them touch your boiler.

After the repair, the system was refilled and re-pressurised to 1.2 bar, the boiler was fired up, and the engineer monitored the pressure over a 20-minute hot cycle to confirm it held steady. The expansion vessel was also checked - its pre-charge pressure was tested using a Schrader valve and a simple gauge. In this case it was within acceptable range, so no further work was needed. Sometimes that check reveals the vessel needs re-charging with air using a compressor, or in older systems, replacement entirely.

The homeowner was shown where the filling loop was located, how to read the pressure gauge correctly, and told clearly: if the pressure drops again within the next four weeks, call us back. It didn't.

What This Cost and How Long It Took

The engineer was on site in Pulborough for just under two hours. The callout and first hour of labour came to around 100 pounds, with the additional time, parts, and system recharge bringing the total to approximately 175 pounds. That's a fairly typical range for this kind of repair in West Sussex - small leak repairs usually fall somewhere between 120 and 220 pounds depending on the location of the fault and the time needed to access it.

If the expansion vessel had needed replacing, that would typically add another 80 to 150 pounds to the bill, covering the part and the additional labour. Expansion vessel replacement on its own commonly costs between 150 and 300 pounds all-in, depending on the vessel size and the boiler model.

A faulty pressure relief valve is a similar job - typically between 100 and 200 pounds to replace, with the part itself costing anywhere from 15 to 50 pounds depending on the boiler brand. Worcester Bosch, Vaillant, Ideal, and Baxi all use slightly different components, and parts for older or less common models can be harder to source quickly.

The repair was booked same-day through Voltrade. That matters in winter, when a boiler that keeps cutting out on low pressure can leave a household without heating or hot water for hours or days.

How to Spot the Same Issue in Your Home

Pressure loss tends to make itself known in a few consistent ways. Here's what to look for:

1. The boiler keeps cutting out or showing a fault code. Most modern boilers - including Worcester Bosch Greenstar, Vaillant ecoTEC, and Ideal Logic models - will lock out and display a fault code when pressure drops below a safe threshold. The code varies by manufacturer, but codes like F22 (Vaillant) or EA229 (Worcester Bosch) commonly relate to low pressure. Check your boiler manual if you see a code you don't recognise.
2. You're topping up the pressure more than once a month. A small top-up after bleeding radiators is normal. Needing to top up repeatedly without having bled any radiators is not. That pattern tells you water is leaving the system somewhere.
3. Radiators are taking longer to heat up or aren't getting hot at the top. Poor circulation linked to low pressure can affect heat distribution. If your upstairs rooms are cold but your downstairs radiators seem fine, check the pressure gauge before you assume it's a balancing or airlocking issue.
4. You can see moisture or staining near pipework, radiator valves, or the boiler itself. Even a tiny drip will eventually leave a ring of limescale or a rust-coloured stain on a nearby surface. Check around all visible pipe connections, under radiators, and anywhere the pipework runs close to the floor or skirting boards.
5. There's water appearing outside the house near the boiler discharge pipe. If the PRV is weeping, the water has to go somewhere. It usually exits via a small plastic pipe that runs through an external wall. Occasional discharge during high-pressure events is normal, but regular dripping means the valve needs attention.

If you're in Pulborough and you're unsure, a quick pressure check takes about 30 seconds. Cold system: the gauge should be in the 1 to 1.5 bar range. Hot system running: up to 2 bar is typically fine. Below 0.5 bar at any point and your boiler is likely to protest.

Lessons - What Every Pulborough Homeowner Should Know

Our engineers see this pattern regularly across West Sussex. A homeowner notices low pressure, tops it up, it drops again, they top it up again - and weeks pass before they call anyone. By that point the system may have been running slightly inefficiently, and in some cases a small drip has had time to cause water damage to nearby joinery, insulation, or electrics.

Here's what we'd tell any homeowner dealing with this:

Don't just keep topping it up. The filling loop on your boiler is there for occasional use - to restore pressure after bleeding or after a repair. It's not meant to compensate for an ongoing leak. Repeatedly topping up masks the symptom without addressing the cause.

Know where your filling loop is before you need it. Many homeowners in Pulborough haven't touched their boiler controls since they moved in. Find the filling loop now, check it's accessible, and make sure you know how to use it correctly. Most are either a flexible braided hose with two valves, or a keyway-style inline valve. Turn on too fast, overshoot 1.5 bar, and you'll create a different problem.

Annual servicing catches this early. A boiler service - which should be done once a year by a Gas Safe registered engineer - includes checks on the expansion vessel pressure, the PRV, and a visual inspection for leaks. In many cases our engineers have spotted a slow-weeping joint or a vessel that's losing its charge during a routine service, long before the homeowner would have noticed anything wrong.

Older systems lose efficiency as components age. If your boiler is more than 10 to 12 years old and pressure loss is becoming a recurring issue, it's worth having an honest conversation with your engineer about whether repeated repairs are better value than a replacement. A new Vaillant ecoTEC or Worcester Bosch Greenstar 4000 installed by a Gas Safe engineer will typically run more efficiently, come with a manufacturer's warranty, and cause far fewer pressure-related headaches.

Pulborough's older housing stock is worth keeping an eye on. Many homes in the village and surrounding areas were built in periods when copper pipe and traditional compression fittings were standard. These systems are reliable, but joints that have expanded and contracted through many winters can develop small weeps. It's not a criticism of the build quality - it's just the nature of ageing plumbing under thermal stress.

Related Questions

Is it safe to keep using my boiler if the pressure is low?

Most modern boilers will lock out automatically when pressure drops below a safe level, so they won't fire up in a dangerous state. That said, running a boiler repeatedly at low pressure - or continually topping it up without finding the cause - isn't a good long-term approach. You should get the system checked by a Gas Safe registered engineer to rule out an active leak before the situation causes further damage to your home or your boiler.

Can I re-pressurise my boiler myself?

Yes, topping up the pressure via the filling loop is something most homeowners can do safely if they follow the manufacturer's instructions. Stop when the gauge reaches 1.2 to 1.5 bar and close the valve properly. What you shouldn't do yourself is any work on the boiler's internal components, gas connections, or sealed pipework. That work legally requires a Gas Safe registered engineer. If you're unsure how to use your filling loop, your boiler manual or a quick call to an engineer is the right move.

How often should boiler pressure drop in a normal system?

A properly sealed system with no leaks and a healthy expansion vessel should hold its pressure for months or years without needing a top-up, except after intentional maintenance like bleeding radiators. If you're topping up more than once every few weeks, that's not normal and warrants investigation. Seasonal variation - where pressure reads slightly differently in summer versus winter - is normal and expected, but it shouldn't be dramatic enough to trigger fault codes.

What happens if the boiler pressure gets too high?

High pressure - typically above 2.5 bar - can cause the pressure relief valve to activate and discharge water, which is exactly what it's designed to do. However, persistently high pressure puts strain on components and seals throughout the system. It commonly results from overfilling via the filling loop, a failed expansion vessel, or a stuck filling loop valve that's allowing mains pressure to bleed into the system. If your gauge is consistently reading above 2 bar when the heating is off, have it looked at.