If your boiler pressure keeps dropping, you’re not alone. Many homes in Exeter and the surrounding areas experience this problem, especially in colder months when heating systems work harder.
A drop in boiler pressure doesn’t always mean a major fault. It can be something as simple as trapped air or a minor leak. But if the pressure drops repeatedly, you shouldn’t ignore it — the issue will only get more costly to fix over time.
At Home Exeter, we regularly diagnose pressure problems as part of boiler servicing and repairs. Here’s what causes low pressure, how to fix it, and when you need a professional.
What Is Boiler Pressure?
Your boiler heats water and circulates it through pipes and radiators. This requires a certain amount of pressure to push the hot water through the system.
Most boilers should sit around:
1.0 to 1.5 bar when cold
Up to around 2.0 bar when heating is on
If the pressure drops below 1.0 bar, your heating and hot water may stop working properly — or shut off completely to protect the boiler.
Top Reasons Your Boiler Keeps Losing Pressure
There are only a handful of common culprits. Some are simple to fix; others require a qualified engineer.
1. A Leak Somewhere in the Heating System
One of the most common causes is a leak in:
- radiator valves
- pipework (often hidden behind floors or walls)
- towel rails
- the boiler itself
These leaks aren’t always visible. A tiny drip can lose enough water to drop the pressure every day.
Signs of a leak include:
- damp patches near radiators or pipes
- rusty radiator valves
- hissing noises from pipes
- visible drips or pooling water
If you suspect a leak, turn the heating off and contact an engineer.
→ Book a boiler inspection with Home Exeter
2. A Faulty Pressure Relief Valve (PRV)
The PRV protects your system by releasing excess pressure. If it becomes damaged or blocked, it can leak constantly — even when pressure is normal.
If you notice a small copper pipe dripping outside your property (usually near an external wall), the PRV may be faulty.
3. Bleeding the Radiators Too Often
Bleeding radiators releases trapped air and increases efficiency. But it also releases water from the system. If you’ve recently bled your radiators and didn’t repressurise the boiler afterward, you’ll notice a drop.
This is especially common after building or decorating work where radiators were removed.
4. Problems With the Expansion Vessel
The expansion vessel helps regulate pressure as the boiler heats up. If the internal membrane fails or deflates, the pressure may rise too quickly, causing the system to dump excess water — and then drop too low again.
This often results in a cycle:
- heating on → pressure rises too high
- PRV releases water
- boiler cools → pressure drops below normal
You’ll need a Gas Safe engineer to re-pressurise or replace the vessel.
→ Speak to a Gas Safe engineer today
5. Faulty Radiator Valves or Corroded Pipe Joints
Older properties are especially prone to wear and tear. Radiator valves can corrode slowly over time, creating small leaks you may not notice until the boiler keeps losing pressure.
Even ultra-small drips add up over weeks and months.
6. Boiler Recently Installed or Serviced
If your boiler or heating system was worked on recently, it may simply need a top-up. Engineers sometimes purposely leave it slightly low so the system can settle. This is usually harmless and fixed within seconds.
However, if pressure keeps dropping after a recent installation, it may indicate a mistake that should be checked.
Is Low Boiler Pressure Dangerous?
Low pressure itself is not usually dangerous, but it can damage your boiler if ignored. Running your boiler at incorrect pressure can increase:
- wear on internal components
- risk of breakdown
- system corrosion
- higher long-term costs
You should never open the casing of your boiler yourself. Only Gas Safe engineers are legally qualified to do so.
What You Can Try Before Calling an Engineer
You may be able to fix minor pressure loss by:
✔ Checking for visible leaks around radiators
✔ Repressurising your boiler using the filling loop
✔ Bleeding radiators only when necessary
✔ Checking all radiator valves are fully closed
If topping up becomes a frequent task (daily or weekly), there’s a deeper issue that needs professional attention.
→ Get help from a trusted local engineer
Why You Shouldn’t Keep Repressurising a Boiler
Many homeowners keep topping up their boiler without fixing the root cause. This can actually make things worse.
Continuous topping up adds fresh oxygen into the system, speeding up corrosion inside radiators and pipework. This can lead to:
- sludge build-up
- blocked heat exchangers
- expensive pump failures
- radiators rusting from the inside out
If you find yourself topping up the pressure more than once every few months, it’s time to book an inspection.
FAQs: Boiler Pressure Problems
How often should I need to top up boiler pressure?
Rarely — ideally once or twice a year at most. Regular topping up means something is wrong.
Can I fix low pressure myself?
You can repressurise using the filling loop, but anything beyond that requires a Gas Safe engineer.
Is it expensive to fix a boiler leak?
Small leaks are often inexpensive if caught early. Ignoring them can lead to costly damage.
Why does the pressure go up when the heating is on?
This is normal. However, if it rises excessively then drops too low afterwards, the expansion vessel or PRV may be faulty.
Can sludge in the system cause low pressure?
Yes. Sludge can prevent water flowing properly and force pressure fluctuations. A system flush may be needed.
Get Your Boiler Pressure Fixed by a Local Expert
If your boiler keeps losing pressure, don’t ignore it. Most issues are simple to repair when diagnosed early — and far cheaper than a full breakdown in winter.
At Home Exeter, we offer:
- Gas Safe and OFTEC-registered engineers
- Accurate diagnosis without guesswork
- Fixed pricing with no hidden charges
- Fast response across Exeter and nearby areas
→ Click here to book your boiler inspection
Restore pressure. Extend lifespan. Avoid costly repairs.
Your boiler will thank you for it.
