A boiler losing pressure can be a frustrating issue for homeowners, especially during the colder months. While some pressure loss is completely normal, consistent or rapid drops could signal a deeper problem. In this blog post, we’ll explore the reasons why boilers lose pressure, how often you should need to top it up, and when it’s time to call in a professional.
Why Does a Boiler Lose Pressure?
Even a tiny leak in your pipework, radiators, or boiler itself can cause the pressure to drop. These leaks may not always be visible, as they can occur in hidden areas like under floorboards or within walls.
Bleeding Radiators
If you’ve recently bled your radiators to remove trapped air, it’s common for the pressure to drop slightly. This is because air escapes from the system, leaving room for water pressure to decrease.
Expansion Vessel Issues
The expansion vessel inside your boiler absorbs pressure changes as the water heats up and cools down. If it’s faulty or needs recharging, the system may lose pressure.
Faulty Pressure Relief Valve
The pressure relief valve (PRV) is a safety feature designed to release water if the boiler pressure gets too high. If it’s damaged or triggered frequently, the boiler may lose pressure and fail to maintain it.
Natural Pressure Fluctuations
Over time, it’s normal for boilers to lose a small amount of pressure due to temperature changes or natural wear and tear.
What Is the Optimal Boiler Pressure?
For most boilers, the optimal pressure is around 1.2 bar when the system is cold. This ensures the system operates efficiently without putting unnecessary strain on the components.
However, if the pressure exceeds 2.0 bar—especially when the system is cold—it can trigger the pressure relief valve (PRV). Once the PRV releases water, it may not fully seal again, which could result in the boiler failing to hold pressure and losing it regularly thereafter.
When topping up the pressure, always aim for 1.2 bar and avoid overfilling the system.
Not All Boilers Will Cut Out When the Pressure Is Low
It’s important to note that not all boilers are designed to cut out when the pressure is low. In some cases, your boiler may continue running even with insufficient water in the system.
This can cause significant damage to internal components, as boilers rely on adequate water levels to function safely. If the system is allowed to run dry, it could result in overheating, cracked components, or even complete boiler failure.
If you notice frequent pressure loss, don’t delay getting it checked—it could save you from costly repairs down the line.
How Often Should You Top Up the Pressure?
For most modern boilers, it’s normal to top up the pressure once or twice a year, especially after bleeding radiators or during seasonal changes. However, if you find yourself needing to top it up monthly, weekly, or even daily, this could indicate a problem that needs attention.
To top up the pressure, use the filling loop on your boiler to bring the pressure to the recommended level of 1.2 bar. Avoid exceeding this level to prevent issues with the PRV.
When Should You Be Concerned?
If your boiler is losing pressure regularly or you notice the following signs, it’s time to call in a professional:
Frequent Top-Ups: Topping up more than every few months could indicate a hidden issue, such as a leak or a faulty component.
Visible Leaks: Damp patches near pipework, radiators, or the boiler itself should be addressed immediately.
Pressure Below 1.0 Bar: If the pressure keeps dropping below 1.0 bar despite topping it up, it could indicate a system fault.
No Heating or Hot Water: A drop in pressure may cause your boiler to stop functioning altogether.
How Gasman Direct Can Help
If your boiler is losing pressure and you’re unsure why, our team at Gasman Direct is here to help. Based in Bognor Regis, we specialise in diagnosing and repairing all types of boiler issues, including persistent pressure loss.
✅ Fast, reliable service
✅ Affordable repairs with no hidden costs
✅ Local experts you can trust
📞 Call us today (01243 933 955) or visit gasmandirect.com to book your appointment. Don’t let low pressure leave you in the cold—or worse, cause long-term damage to your boiler!