Why Is My Boiler Losing Pressure?
Low or dropping boiler pressure is one of the most common heating problems. Here's what causes it, how to repressurise, and when to call an engineer.
Gas Safe Registered · 587401
Manufacturer Approved
Fully Insured
Same-Day Service
Local Engineers
Upfront cost — no obligation If your boiler pressure keeps dropping or the gauge is in the red low zone, you’re not alone — it’s one of the most common boiler problems we’re called about. Low pressure stops the boiler working properly and is often easy to top up, but if it keeps falling there’s usually an underlying cause that needs fixing. This guide explains why it happens and what you can safely do.
What boiler pressure should be
Most boilers should sit at around 1 to 1.5 bar when cold, rising a little when the heating is on. If your gauge reads below 1 bar, the boiler may lock out or fail to heat. A pressure that drops slowly over weeks can be normal topping-up territory; a pressure that drops quickly or repeatedly points to a fault.
Most boilers should sit at around 1 to 1.5 bar when cold, rising a little when the heating is on.
How to repressurise your boiler
Most boilers can be repressurised using the filling loop — a flexible braided hose or built-in valve beneath the boiler. With the boiler off, open the valve(s) slowly to let water in, watch the gauge rise to around 1.5 bar, then close the valve(s). Your boiler manual shows the exact method for your model. If you’re not comfortable doing this, an engineer can show you.
Most boilers can be repressurised using the filling loop — a flexible braided hose or built-in valve beneath the boiler.
Why pressure keeps dropping
If you’re repressurising often, something is wrong. The usual causes are a leak somewhere in the system (radiators, pipework or the boiler itself), a faulty pressure relief valve releasing water outside, or a waterlogged expansion vessel that can no longer absorb pressure changes. These all need a Gas Safe engineer to diagnose and repair — topping up repeatedly only masks the problem.
If you’re repressurising often, something is wrong.
We fix pressure faults across East London
If your boiler won’t hold pressure, Gas First can find and fix the cause across East London and Essex — locating leaks, replacing failed valves, or recharging the expansion vessel. Call us if you’re topping up more than occasionally.
If your boiler won’t hold pressure, Gas First can find and fix the cause across East London and Essex — locating leaks, replacing failed valves, or…
Frequently Asked Questions
What pressure should my boiler be at?
Around 1 to 1.5 bar when cold for most boilers, rising slightly when heating is on. Below 1 bar usually causes problems.
How do I repressurise my boiler?
Use the filling loop beneath the boiler: with the boiler off, slowly open the valve(s) to let water in until the gauge reaches about 1.5 bar, then close them. Check your manual for the exact method.
Why does my boiler keep losing pressure?
Repeated loss usually means a leak in the system, a faulty pressure relief valve, or a waterlogged expansion vessel — all needing an engineer to fix.
Is low boiler pressure dangerous?
It's not usually dangerous — the boiler typically just stops working. But the underlying cause, such as a leak, should be addressed.
How often should I need to top up the pressure?
Only occasionally. If you're repressurising every week or two, there's a fault that needs investigating.
What Our Customers Say
Rated 5 stars by homeowners and landlords across East London
“Landlord gas safety certificate done in Rainham. Came on time, kept me informed and the tenants and delivered a clean, tidy and efficient service. Highly recommended. Will use again.”
Kamal Miah | Rainham, Essex
“Gas safety checks for properties.”
Jay Alam | Ilford, East London
“I would highly recommend Julhas the boiler engineer. He installed a new pump for me and successfully sorted out both the hot water and heating issues I was experiencing. Throughout the job, he was informative, honest, and professional, taking the time to explain everything clearly. His pricing was very reasonable, and what impressed me most was how thorough he was. He never rushed the work and made sure everything was completed properly and to a high standard. I will definitely be using him again when my boiler is due for its annual service next year. A first-class service from start to finish. Thank you!!”
Mai-Yee Ramiro | East London
Get a Free Quote
Fill in the form and we'll call you back as soon as possible
Quick Booking
📞 We'll call you back
Why Choose Gas First Ltd?
Professional, reliable, and certified gas engineering services across East London
Gas Safe Registered
All work carried out by fully certified Gas Safe engineers
Fast Emergency Response
Quick attendance for urgent gas & heating issues across East London
Transparent Pricing
Fair quotes with no hidden charges — you know the cost upfront
5-Star Customer Service
Rated highly by homeowners & landlords across East London
Experienced Local Engineers
Skilled team covering all East London boroughs
Domestic & Commercial
Services for homes, rentals, and businesses
Areas We Cover
We provide gas, boiler, and plumbing services across East London and nearby areas.
Need a Reliable Gas Engineer in East London?
Contact Gas First Ltd today for fast, professional gas, boiler, and plumbing services across East London.