Why Does My Boiler Pressure Keep Dropping? Causes & Fixes
If your boiler pressure keeps dropping even after you’ve topped it up, there’s almost always a leak or fault somewhere in the system causing it to lose water repeatedly. A one-off drop is usually harmless, but a pressure that keeps falling again and again is a sign of an underlying problem.
We’re Hinckley Plumbing & Heating, established and professional Gas Safe registered engineers covering Hinckley, Nuneaton, Leicester, Tamworth, Coventry, Rugby, and Loughborough — and this guide explains why your boiler pressure keeps dropping, what you can check yourself, and when to call us if you need a boiler repair.
What Does It Mean If My Boiler Pressure Keeps Dropping?
Boilers are sealed, pressurised systems that should hold a stable pressure once topped up correctly. If the pressure keeps dropping over hours, days, or weeks, water is escaping from the system somewhere, even if you can’t see it.
A single drop after bleeding a radiator or during a service is normal. Repeated drops without an obvious cause are not.
What Causes Boiler Pressure To Keep Dropping?
The most common causes of boiler pressure repeatedly dropping are:
- A hidden leak somewhere in the pipework or under floorboards
- A leaking radiator valve or bleed valve
- A faulty pressure relief valve letting water escape
- A failed expansion vessel that can no longer absorb pressure changes correctly
- A leaking heat exchanger inside the boiler itself
- A faulty filling loop that hasn’t been fully closed
How Often Is Normal For Boiler Pressure To Drop?
Some very gradual pressure loss over several months is considered normal wear. If you’re topping up the pressure more than once every few weeks, or the pressure drops noticeably within days, that points to an active leak or fault rather than normal system ageing.
What Should I Check If My Boiler Pressure Keeps Dropping?
Before calling an engineer, it’s worth checking:
- All visible radiators and pipework for damp patches, drips, or staining.
- Under the boiler for any pooling water.
- Radiator valves for any signs of weeping or corrosion.
- The filling loop to make sure it’s fully closed, not just loosely shut.
- The pressure relief valve pipe outside the property for dripping.
If you can’t find a visible leak but the pressure keeps dropping, the fault is likely hidden or internal to the boiler.
Why Does My Boiler Pressure Keep Dropping Even After Topping Up?
Topping up the pressure only refills the system — it doesn’t fix whatever is causing the water to escape in the first place. If the pressure drops again shortly after you’ve corrected it, that confirms an active leak or internal fault that needs proper diagnosis rather than repeated top-ups.
When Should You Call Us About Dropping Boiler Pressure?
Call Hinckley Plumbing & Heating if:
- You’re topping up the pressure more than once a month
- The pressure drops within a day or two of topping up
- You can hear the boiler cycling on and off unusually
- You’ve noticed damp patches, staining, or pooling water anywhere near pipework
- The boiler shows a low-pressure fault code alongside the dropping pressure
- You can’t find any visible cause for the drop
Book A Boiler Pressure Diagnosis
If your boiler pressure keeps dropping and you can’t find the cause, we can help. We cover Hinckley, Nuneaton, Leicester, Tamworth, Coventry, Rugby, and Loughborough, and we’ll trace exactly where the system is losing pressure and give you a clear, honest assessment of the fix needed. Call us or use our contact form to book a boiler inspection.
Boiler Pressure Keeps Dropping FAQs
Is it normal for boiler pressure to drop slightly over time?
A very slow drop over several months can be normal. Anything faster or more frequent usually means a leak or fault.
Can low boiler pressure damage my boiler?
Yes. Running a boiler at low pressure for long periods can cause it to lock out repeatedly and may put additional strain on internal components.
Why does my boiler pressure drop only when the heating is on?
This can point to a leak that only shows up under the extra pressure of the heating cycle, such as a weeping valve or joint that only leaks when hot.
Can I just keep topping up the pressure myself?
You can in the short term, but repeatedly topping up without finding the cause means the underlying leak or fault is left unresolved and could get worse.