If you’ve noticed water dripping from a copper pipe outside your home or beneath your boiler, it’s often a sign of a pressure relief valve (PRV) leak. This is a common cause of ongoing boiler pressure loss and usually indicates an underlying issue within the heating system rather than just a faulty valve.
While it may seem minor at first, a PRV leak often points to pressure problems, expansion issues, or hidden faults that need proper investigation.
Why a PRV starts leaking
The pressure relief valve is designed to release water if system pressure becomes too high. However, once it opens, it doesn’t always reseal properly — especially if there’s an ongoing fault.
Common causes include:
- Expansion vessel failure causing pressure spikes
- System overfilling from repeated topping up
- Debris preventing the valve from sealing fully
- Wear and tear on older components
Why this leads to pressure loss
Every time the PRV releases water, the system loses pressure. This is why homeowners often notice they need to keep topping up the boiler, even though no internal leaks are visible.
In many cases, the PRV isn’t the root cause — it’s reacting to another issue within the system.
Signs the PRV is the problem
You may be dealing with a PRV-related issue if:
- Water is dripping from an external copper pipe
- Boiler pressure keeps dropping after topping up
- There are no visible leaks inside the property
- The issue started after repressurising the system
Why it shouldn’t be ignored
Leaving a PRV leak unresolved can lead to:
- Repeated pressure loss
- Boiler lockouts
- Increased wear on system components
- Hidden issues going undiagnosed
Simply topping up the system doesn’t fix the problem — it often makes it worse over time.
The takeaway
A leaking pressure relief valve is rarely just a faulty part. It’s usually a symptom of a wider issue within the heating system that needs to be identified properly.
For a full breakdown of causes and pressure behaviour, see our central heating leaks explained guide.
For ongoing pressure issues or suspected leaks, our central heating leak detection service can trace the cause accurately without unnecessary disruption.