How To: Top Up Pressure on a Sealed Heating System

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Low boiler pressure? Learn how to safely top up your sealed heating system and ensure optimal performance with our simple step-by-step guide.

Is your heating system not performing as well as it should? One of the most common issues in modern sealed heating systems is low pressure. When your system pressure drops below the recommended level, your heating efficiency decreases and your boiler may even shut down as a safety precaution. Fortunately, topping up the pressure is a straightforward task that many homeowners can do themselves.

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Understanding Pressure in Your Heating System

Modern sealed heating systems (also called pressurised or closed systems) require a specific pressure to function correctly. This pressure ensures hot water circulates efficiently throughout your radiators and provides consistent heating throughout your home.

The pressure is measured in "bar" and is typically displayed on a pressure gauge located on your boiler. For most domestic systems:

• 1 to 1.5 bar is the ideal pressure when the system is cold
• Up to 2 bar is normal when the system is hot (as water expands when heated)
• Below 0.5 bar is too low and may cause the system to shut down
• Above 3 bar is too high and may cause safety valves to release water or even damage components

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When to Top Up Your System

You should check your boiler pressure periodically, especially if you notice:

• Radiators not heating up properly
• Boiler cutting out unexpectedly
• Error codes on your boiler display related to pressure
• The pressure gauge showing readings below 1 bar

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Step-by-Step Guide to Topping Up Your System

What You'll Need

• Knowledge of where your filling loop is located (typically underneath or near your boiler)
• A basic understanding of your boiler's pressure gauge

Step 1: Turn Off Your Heating

Before beginning, ensure your heating system is turned off and has cooled down. Working with a cold system gives you the most accurate pressure reading.

Step 2: Locate the Filling Loop and Pressure Gauge

The filling loop is usually a flexible silver hose with valves at either end, connected to your boiler's pipework. The pressure gauge is typically on the front of your boiler or on the control panel, showing a needle or digital display indicating the current pressure.

Step 3: Open the Valve

Gently turn the valve on the filling loop anti-clockwise (to the left) to open it. Some systems may have two valves that need to be opened.

Step 4: Monitor the Pressure Gauge

As you open the valve, watch the pressure gauge closely. You'll see the needle begin to rise (or the digital reading increase).

Step 5: Reach the Correct Pressure

Allow the pressure to rise to approximately 1.5 bar. This is the ideal pressure for most heating systems when cold.

Step 6: Close the Valve

Once you've reached the correct pressure, turn the valve clockwise (to the right) to close it securely. If your system has two valves, ensure both are firmly closed.

Step 7: Check the System

Turn your heating back on and check that the system is working correctly. As the water heats up, the pressure may rise slightly (up to about 2 bar), which is completely normal due to the thermal expansion of water.

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Important Safety Considerations

• Never increase the pressure above 2 bar when the system is cold
• If your pressure regularly drops, this could indicate a leak in your system
• If your pressure rises above 3 bar, this could be dangerous and requires professional attention
• If you're unsure about any aspect of topping up your system, contact a professional heating engineer

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When to Call BeeXpress

While topping up your heating system pressure is generally a simple DIY task, there are situations where professional help is necessary:

• If you need to top up your system frequently (more than once a month)
• If you notice any leaks from radiators, pipes, or the boiler itself
• If the pressure continues to rise without explanation
• If your boiler displays persistent error codes even after topping up
• If you're uncomfortable performing the procedure yourself

At BeeXpress, our Gas Safe registered engineers can diagnose and fix any pressure-related issues with your heating system. We can identify hidden leaks, replace faulty pressure relief valves, check expansion vessels, and ensure your system operates safely and efficiently.

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Preventative Maintenance Tips

To maintain optimal pressure in your heating system:

• Schedule annual boiler servicing to catch problems early
• Check your pressure gauge monthly during the heating season
• Look for signs of leaks around radiators and visible pipework
• Consider a system power flush if your system is older (5+ years)

Keeping your heating system at the correct pressure not only ensures efficient operation but also extends the life of your boiler and reduces energy consumption, saving you money on both repairs and energy bills.

Need professional assistance with your heating system pressure? Contact BeeXpress today—your trusted heating engineers in North West London.

Watch our demonstration video on our YouTube channel for a visual guide to topping up your heating system pressure.