Boiler Losing Pressure Constantly in Horsham? The 3 Causes & When to Call an Engineer

Is your boiler flashing a low-pressure fault code, forcing you to top up the pressure every morning? 

This isn't just an inconvenience; it's a sign that your sealed central heating system is losing water somewhere. 

For homeowners in the Horsham District, Adur District, and across West Sussex, consistent pressure loss is rarely a random event. 

It's usually caused by one of three things. 

As your trusted local experts at Prime Boiler Care, based in Horsham, we’ve broken down the likely culprits, starting with the simplest. 

The 3 Most Common Causes of Boiler Pressure Loss. 

Cause 1: A Visible Leak in the System (The Most Common) A leak—even a tiny, slow drip—is the most frequent reason for a pressure drop. 

Where to Check: Inspect pipework, especially at joints, radiator valves, and under the boiler casing. 

Look for damp patches, visible water, or mineral deposits (calcium build-up from slow evaporation). 

DIY Action: If you find a tiny leak at a radiator spindle, try tightening it gently with a spanner. 

If the leak is from the boiler itself, do not attempt a DIY fix. 

Urgent Internal Link: If you find cold spots on your radiators, it might be air, not a leak. 

Please read our guide on Bleeding and Balancing Radiators to rule that out. 

Cause 2: Faulty Pressure Relief Valve (PRV) The PRV is a safety mechanism designed to release excess pressure, typically through a pipe that extends to an outside wall. 

If the PRV is faulty, it can drip constantly, draining water and pressure from the system. 

The Sign: Check the pipe that runs out from your boiler to the exterior wall. 

If you see water constantly dripping or running down the wall when the boiler is off, your PRV is likely stuck open. 

Engineer Action: This requires a qualified Gas Safe engineer from Prime Boiler Care to diagnose and replace the valve. 

Cause 3: A Faulty Expansion Vessel (The Internal Problem) 

The expansion vessel absorbs excess water volume when the system heats up. 

If the vessel loses its air charge, it can't regulate the pressure, causing it to drop every time the boiler cools down. 

The Sign: You will notice a dramatic pressure drop when the boiler is cold and a rapid, high-pressure spike when it's hot. 

Engineer Action: This is an internal component that only a professional should repressurise or replace. 

When Do You Need a Local Gas Engineer? 

You should always call a qualified engineer from Prime Boiler Care if: The pressure drops again within 24 hours of you repressurising it. 

You see any leak coming directly from the boiler casing or pipework underneath it. 

Your boiler repeatedly locks out and displays a fault code. 

Don't live with a constantly failing boiler. 

If you’re struggling with pressure loss in the Horsham District or Adur District, call Prime Boiler Care today for a rapid, reliable fault diagnosis from a local Gas Safe-registered expert. 

Call us today 01403 814602

Prime Boiler Care

Suite 54, Standby Business Centre,

Foundry Lane, Horsham, West Sussex, RH13 5PX