How to repressurise a boiler

If you are struggling to get hot water or central heating, it may be that you need to repressurise your boiler. Low boiler pressure can be caused by water leaks or excessively bleeding radiators and force the boiler to shut down as a safety precaution.

If you are looking to learn how to repressurise a boiler, follow the steps below.

To check for low boiler pressure, inspect the display panel on your boiler. Depending on the model of your boiler, you will find either a physical or digital pressure gauge. The dial (or bar) will tell you the level of pressure in the system.

The typical level to aim for is around 1 - 1.5 bar; any less and it is likely that your boiler will need to be repressurised. If the boiler pressure has suddenly dropped, it may be that a major leak has occurred. Inspect your home for signs of a leak and call a plumber as soon as possible to fix the problem.

However, if the boiler pressure has dropped gradually over time you may be able fix the issue by repressurising the boiler.

Always begin the process of repressurising your boiler by checking your boiler manual. Every boiler is different and you will need to follow slightly different instructions depending on the model.

As a general guide, follow these steps:

1. Turn off the boiler. The entire heating system needs to cool before work can be carried out on it.

2. Inspect the boiler filling loop. This is a silver connection between the mains and the primary central heating circuit. One end will have a handle valve while the other end will have an isolation valve. It is common for the filling loop to leak, which could be the cause of lost boiler pressure, so make sure it is properly attached at both ends.

3. Turn the isolation valve anti-clockwise until the line on the valve is directly in line with the pipe. A flat head screwdriver is usually the best tool for this.

4. Turn the handle valve anti-clockwise. This allows water to flow through the system, rebalancing the pressure levels.

5. Watch the pressure gauge as you do this. You should see the gauge increase as you open the handle valve. Stop once it reaches the recommended level for your boiler.

6. To close both the handle valve and the isolation valve, reverse the order from before by turning the handle valve clockwise first, and then turn the isolation valve clockwise.

7. Turn the boiler on and check to see if it is now working correctly.

Not all boilers are compatible with a filling loop; this is particularly true for older combi boiler models. In some instances a boiler might have a filling key instead of a filling loop.

The steps for repressurising a boiler using a filling key instead of a filling loop are slightly different:

1. Turn off the boiler.

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

3. Turn the valve next to the key until water flows through it. The best tool to use is either a wrench or a spanner.

4. Monitor the valve until it reaches the recommended level for your boiler model. This will be outlined in the boiler manual.

5. Close the valve and turn the boiler back on.

If you have followed the steps above but your boiler’s pressure levels drop as soon as you close the valve, it is highly likely that there is a significant leak. There may also be a fault with your pressure release valve.

In this instance, call a Vaillant installerto inspect your boiler system. Do not keep trying to repressurise the system, as this could potentially cause further damage.

• Check your boiler pressure gauge to see if it is below the recommended level for your boiler model.
• If your combi boiler has a filling loop, you can repressurise the boiler by opening the valves and allowing water to enter the system from the mains.
• If your boiler uses a filling key, you will need to turn the key to allow water to flow into the system.
• If you require further help to repressurise your boiler, call a qualified engineer to fix the problem.