Boiler keeps losing pressure
Check the steps below first — if you're not confident, get it fixed safely today.
Post a job — we'll find you an engineer →A boiler that needs regular pressure top-ups is one of the most common issues we see in British homes, and it's always a sign that water is escaping somewhere in your heating system. Because your boiler and radiators form a sealed circuit, water shouldn't disappear — if you're topping up more than once a month, there's definitely a leak hiding somewhere, whether it's visible or tucked away behind pipework. The good news is that most leaks can be found with a simple visual inspection, and catching them early prevents bigger problems like water damage or a completely failed boiler. This guide walks you through the checks you can do yourself before calling in a Gas Safe engineer, which saves time and money.
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Most likely cause & what to check
Topping up the boiler more than once a month means there is a leak somewhere — water doesn't disappear on its own in a sealed system.
Do a quick visual check: look at all visible radiator valves and pipe joints for any damp, rust staining, or white limescale marks. Also check the small pipe that exits outside (pressure relief valve discharge) for any dripping.
If you can't find anything obvious, call a Gas Safe engineer. Tell them: "My boiler keeps losing pressure and needs topping up regularly — I've checked for visible leaks but can't find anything."
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Frequently asked questions
Is it normal for a boiler to lose pressure?
A tiny amount of pressure loss over several months can be normal, but needing to top up more than once a month definitely isn't. If your boiler is regularly dropping below the safe operating range, there's a leak that needs finding and fixing.
Can I keep topping up the boiler instead of fixing the leak?
You can temporarily, but it's not a solution and may mask a serious problem. A persistent leak wastes water, can damage your home's structure or electrics, and leaves your boiler working harder — eventually it'll fail completely and replacement is expensive.
Where do boilers usually leak from?
The most common culprits are radiator valve seals, compression fittings on pipes, and the pressure relief valve discharge pipe outside. Internal leaks in the heat exchanger are less common but more serious, which is why a Gas Safe engineer's diagnosis matters.
What should I do if I can't find the leak myself?
Call a Gas Safe registered engineer and describe exactly what's happening — mention the pressure drop frequency and that you've already checked for visible water. They have specialist equipment to locate hidden leaks and can safely diagnose internal issues you can't see.
How much does it cost to fix a boiler pressure leak?
It depends on the source — a simple valve replacement or joint tightening might cost £50–150, whilst internal heat exchanger repairs could run into hundreds. Getting a proper diagnosis first means you'll know the actual cost before committing.
Will my boiler be safe to use while it's losing pressure?
As long as the pressure stays within the safe operating range (usually marked on your boiler's gauge), it's safe to use. However, if pressure drops below the minimum line, your boiler will lockout — this is a safety feature, so don't ignore it.