If you’ve noticed your boiler pressure dropping, you’re experiencing one of the most common issues we encounter as boiler installers in Whitstable. A boiler losing pressure can be frustrating, especially when it impacts your heating system’s performance during colder months.

Following on from our previous guide about understanding boiler pressure, we’re diving deeper into the specific causes of pressure loss and providing step-by-step solutions to get your heating system back to optimal performance.

Common Reasons Why Boilers Lose Pressure

Understanding why your boiler keeps losing pressure is the first step towards an effective solution. Here are the most frequent culprits:

1. Water Leaks in Your Heating System

Even tiny, almost invisible leaks can cause gradual pressure loss over time. These leaks might occur in:

• Radiator valves: Particularly where the spindle meets the body of the valve
• Pipe joints: Especially in hidden areas like under floorboards or behind walls
• Radiator bodies: Small pinholes can develop due to internal corrosion
• Boiler components: Internal parts like the heat exchanger or pump seals can develop leaks

Water leaks not only cause pressure drops but can also lead to water damage and reduced system efficiency. Look for damp patches, water stains, or corrosion around your radiators and visible pipework.

2. Recently Bled Radiators

When you bleed your radiators to remove trapped air, you’re also releasing water from your system. If you’ve recently bled multiple radiators, this could explain the pressure drop. This is normal and easily remedied by repressurising your system.

3. Pressure Relief Valve Discharge

Your boiler has a pressure relief valve (PRV) that activates if the pressure gets too high, typically above 3 bar. This safety feature protects your system from excessive pressure by releasing water, which consequently lowers the pressure.

If your PRV has activated, you might notice water dripping from the external discharge pipe. This could indicate that your system was over-pressurised or that the PRV needs attention.

4. Faulty Expansion Vessel

The expansion vessel contains a rubber diaphragm that helps absorb the natural expansion of water when heated. If this diaphragm becomes damaged or loses its charge, the vessel cannot function correctly, leading to pressure fluctuations.

Signs of a faulty expansion vessel include:

• Pressure dropping when the boiler cools down
• Pressure rising excessively when the heating is on
• The PRV repeatedly activating

5. Automatic Air Vents Releasing Water

Automatic air vents (AAVs) are designed to release trapped air from your system. However, faulty AAVs might also release water, causing pressure loss over time.

How to Fix a Boiler That Keeps Losing Pressure

Depending on the cause, here’s how to address boiler pressure loss:

Repressurising Your Boiler

If the pressure drop is due to normal causes like radiator bleeding, repressurising is a straightforward fix:

1. Ensure your boiler is switched off and cool – Never adjust pressure on a hot system.
2. Locate the filling loop – This is usually a flexible silver hose with two control valves, connected to your boiler or nearby pipework.
3. Open both valves slowly – Turn them anticlockwise to allow water to enter the system. You should hear water flowing.
4. Monitor the pressure gauge – Watch as the needle or digital display rises. Aim for 1.0-1.5 bar.
5. Close both valves when desired pressure is reached – Turn them clockwise to fully closed position.
6. Vent any trapped air – You might need to bleed radiators again if you hear gurgling.
7. Switch the boiler back on – Check that the pressure remains stable once the system heats up.

Checking for and Fixing Leaks

For persistent pressure loss, you’ll need to check for leaks:

1. Visually inspect all accessible pipework and radiators – Look for water marks, damp patches, or corrosion.
2. Tighten any loose radiator valves – Use an adjustable spanner, being careful not to overtighten.
3. Check radiator valve glands – These can often be tightened slightly to stop minor leaks.
4. Feel along the bottom of radiators – Tiny pinholes might only show as slightly damp areas.

For hidden leaks, professional detection equipment may be required. This is where a qualified heating engineer becomes essential.

Addressing Expansion Vessel Issues

If you suspect a faulty expansion vessel:

1. Check the vessel’s pressure – This requires a pressure gauge and should be done by a professional.
2. Recharge if necessary – An expansion vessel typically needs a pressure of around 1 bar when the system is depressurised.
3. Replace if damaged – If the diaphragm is damaged, the entire vessel may need replacement.

When to Call a Professional

While repressurising your boiler is something you can handle yourself, you should call a Gas Safe registered engineer if:

• You’ve repressurised multiple times and the pressure continues to drop
• You suspect a leak but cannot locate it
• The pressure relief valve is frequently discharging water
• Your expansion vessel appears to be faulty
• You’re not confident in making adjustments yourself

Persistent pressure issues often indicate underlying problems that require professional attention. Ignoring these can lead to inefficient heating, increased energy bills, and potentially expensive damage to your boiler.

Our team of experienced Gas Safe engineers in Whitstable can perform a thorough diagnosis of your heating system, identifying and resolving the root cause of pressure loss. For expert assistance with your boiler pressure issues, contact us for prompt, professional service.