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How to Repressurise Your Boiler: A Step-by-Step Guide

If your Glow-worm boiler is showing low boiler pressure, it may be time to repressurise. Low boiler pressure can affect heating performance, leading to cold radiators, uneven heating, or even a shutdown of your heating system.

Here’s our comprehensive, step-by-step guide on how to repressurise a boiler safely and quickly.

Why Is Boiler Pressure Important?

Glow-worm boilers, like other heating systems, need stable pressure to work effectively. The pressure gauge on your Glow-worm boiler should generally read between 1 and 1.5 bar. If the boiler pressure is low, you might experience uneven heating or a complete loss of hot water.

How to Check Boiler Pressure on your boiler

Before you repressurise, check your boiler’s digital display. Start by turning the heating and hot water off, allowing the boiler to cool. If the display reads less than 1, the boiler pressure is low, and it’s time to take action.

Step-by-Step Guide: How to Repressurise a Glow-worm Boiler

Repressurising a Glow-worm boiler is a straightforward process. Here’s how to do it, step by step:

Locate the Filling Loop on the Boiler

The filling loop is a flexible silver hose that connects two small valves underneath your Glow-worm boiler. The filling loop is used to add water to your system, which increases the pressure.

*If you can’t find the filling loop, refer to your boiler’s manual. All manuals for our current boiler range can be found here.

Turn Off the Boiler and Wait for It to Cool

Ensure that the heating and hot water are switched off and wait a couple of minutes for the pipes below the boiler to cool down. This will prevent any potential burns or injury from the hot water inside the system.

It’s also important to make sure the system is not actively circulating water when you open the valves, as this could interfere with the repressurising process.

Open the Valves to Add Water

Slowly turn both valves (or lever) on either side of the filling loop 90 degrees counterclockwise. You’ll begin to hear water flowing into the system. As the water enters, the pressure inside the boiler will increase.

Carefully watch the boiler pressure rise.

Tip: Turn the valves slowly to avoid letting too much water in at once. Repressurising a Glow-worm boiler requires precision, and going too fast can cause you to overfill the system.

Stop When Boiler Pressure Reaches 1 to 1.5 Bar

Keep the valves open until the display reads between 1 and 1.5 bar. This is the ideal pressure for most Glow-worm boilers.

Avoid letting the pressure rise above 2.5 bar, as this can cause damage to the boiler and the entire heating system. If the pressure exceeds this range, it’s a sign you may need to bleed your radiators to release some of the excess water.

*If the pressure gauge jumps too quickly, stop and check the system. If the pressure rises too fast, it could indicate a problem with the valve or pressure system.

Turn Off the Valves

Once the pressure reaches the ideal range (between 1 and 1.5 bar), turn both valves or levers clockwise to shut them off. This will stop the water flow and prevent further changes to the boiler pressure.

Make sure the valves are securely closed to avoid leaks or drops in pressure later on.

Tip: Double-check the valves to ensure they’re fully closed. Even a small leak can cause the pressure to drop again.

Remove the Filling Loop (If Detachable)

If your Glow-worm boiler has a detachable filling loop, carefully remove it once the pressure is at the correct level. This prevents accidental adjustments to the pressure and keeps the loop from getting damaged.

Store the loop in a safe place for future use, in case you need to repressurise your boiler again later.

*If your filling loop is fixed, make sure it’s securely stored so it won’t get in the way of other boiler components.

Check the Pressure Gauge Again

When you complete the re-pressurising process, the boiler will start an automatic purge mode, which lasts 5 minutes.

During this mode, the pressure reading will fluctuate, and the heating and hot water won't work. This is normal. After 5 minutes the pressure will return between 1 – 1.5 bars and your boiler will be ready to use again.

After 5 minutes, check the display again to ensure that it’s still within the optimal range of 1 to 1.5 bar and remains steady while the system is running, and the boiler will be ready to use again.

How To Repressurise A Boiler Without A Filling Loop

Some boilers don’t always have a filling loop; this is usually the case for older models of combi boilers. This means that you may have a filling key instead of a filling loop. If you’re unsure, check your boiler manual.

Here are the steps for repressurising a boiler without a filling loop:

1. Turn off your boiler and wait for the whole heating system to cool down.

2. Insert the filling key into the keyhole to unlock it.

3. Turn the valve next to the key until water flows through it. We recommend that you use either a spanner or wrench to do this.

4. Keep checking the valve until it reaches the recommended level for your boiler.

5. Close the valve and turn your heating system back on.

Final Steps: Ensuring Your Glow-worm Boiler Works Efficiently

After you repressurise your Glow-worm boiler, turn it on and check that it’s heating evenly and that the pressure gauge remains stable.

Regular maintenance like this helps your boiler run efficiently and prevents low boiler pressure issues.

My boiler’s pressure has dropped again, what do I do now?

If your boiler pressure continues to drop or you notice any unusual behaviour, don’t hesitate to reach out to your local Gas Safe registered engineer. Proper boiler pressure is key to ensuring your heating system runs at its best, keeping your home warm and comfortable all year long.

By following these detailed steps, you can easily repressurise your Glow-worm boiler and keep your heating system running efficiently. Regularly checking and maintaining your boiler pressure is crucial to avoiding common issues like low boiler pressure and uneven heating. If you’re unsure at any stage or need more advice, contact a professional to ensure your Glow-worm boiler stays in top condition.

Need help repressurising your boiler?

Contact your local Glow-worm installer here

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