Advice from Paul · Gas Safe #221708

Why does my boiler keep losing pressure?

In short: A boiler loses pressure because water is escaping the system somewhere: usually a small leak on a pipe, radiator or the boiler itself, a failed pressure relief valve, or a waterlogged expansion vessel, and occasionally just from bleeding radiators.

Call Paul · 0151 440 2614 Boiler repair in Liverpool
  • 5.0 on Google · 126 reviews
  • Gas Safe #221708
  • 40 years on the tools
  • Paul answers the phone himself
Hidden pipe leak traced and repaired by Paul
Hidden pipe leak traced and repaired by Paul

If you keep having to top your boiler up because the pressure drops, the system is losing water somewhere, water does not just vanish. Sometimes it is harmless, but a boiler that constantly loses pressure usually has a small leak or a failing part that is worth finding before it gets worse.

Here is what causes it and what is worth checking, from a Gas Safe engineer’s point of view.

Where the pressure is going

If you are topping up more than very occasionally, one of these is usually the culprit.

  1. 01

    A small leak somewhere

    The most common cause. A weeping joint, a pinhole on a pipe, a leaking radiator valve or a leak inside the boiler all let water out slowly, dropping the pressure. Some are visible; hidden ones need tracing.

  2. 02

    A failed pressure relief valve

    If this valve is passing, water escapes through the outside overflow pipe, often you will see it dripping outside. It needs replacing by an engineer.

  3. 03

    A waterlogged expansion vessel

    The expansion vessel absorbs pressure changes as water heats up. When it fails, pressure swings and drops. Re-charging or replacing it is an engineer’s job.

  4. 04

    Recently bled radiators

    If you have just bled your radiators, a small pressure drop is normal, top it up once and see if it holds. If it keeps dropping, it is one of the causes above.

What to do about it

Topping the boiler up occasionally is fine, but if you are doing it every week or few days, do not just keep topping up, there is a leak or a faulty part that needs finding and fixing. Constant fresh water into the system also causes corrosion and sludge over time.

A Gas Safe engineer can trace the leak or test the parts and put it right, so you are not forever topping it up.

Rather just get it sorted?

If your boiler keeps losing pressure, ring Paul to find the cause

You get Paul on the phone, a Gas Safe engineer with 40 years behind him, not a call centre. He will give you a straight answer and a fair fixed price. See boiler repair for how he can help.

Call 0151 440 2614 Boiler repair in Liverpool

Straight answers

Common questions

Is it normal for a boiler to lose pressure?

A tiny, very occasional drop can be normal, especially after bleeding radiators. But if you are topping it up every few days, water is escaping somewhere and it needs looking at.

Can I just keep topping my boiler up?

Only as a short-term measure. Constant topping up means an unfixed leak or faulty part, and all that fresh water causes corrosion and sludge over time. Better to have the cause fixed.

How do you find where a boiler is losing pressure?

Paul checks the visible joints, radiators, valves and the boiler, tests the pressure relief valve and expansion vessel, and traces any hidden leak, then fixes the actual cause rather than guessing.

More helpful guides

Boiler keeps turning off? Why is my boiler not working?

Honest advice, then a proper fix

Still stuck? Give Paul a bell.

Forty years on the tools, Gas Safe registered, and the fella who quotes it is the fella who does it. No call centre, no pushy sales.

Call Paul · 0151 440 2614 Boiler repair in Liverpool
Call Paul now Quote