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How to Refill or Re-Pressurise a Combi Boiler

When bleeding radiators or carrying out alterations to a combi boiler central heating system the boiler can switch off due to not enough pressure. Some models have a pressure gauge on the front of the boiler to indicate when the pressure is low or high. When the indicator is below 1 the system may switch off or you may notice the heating not preforming as well as usual.‹¯¨

Some boilers have an internal filling loop and others have an external filling hose. For either methods of refilling, you MUST turn the power off to the boiler first.

1. If your appliance has an internal filling loop installed within the boiler you will need to remove the tray at the bottom. Here you will find the filling key attached to the tray.
2. Remove the key from the tray and locate the manifold into which you will need to insert the key. This filling manifold is actually linked from your cold mains to the boiler through to your central heating return.
3. What you will then need to do is fit the key into the manifold with the arrow on the key facing the open padlock position. You then turn it to the locked padlock position.
4. You will then begin to turn the plastic nut located next to where the key was inserted anticlockwise. You should begin to hear the water filling the boiler.
5. Once you have done that you need to concentrate on the pressure gage; you should be able to see it filling up. Once it is up in the green zone to the required 1.5 you will begin to tighten the nut you unscrewed momentarily, until you can actually hear the water stop.
6. Turn the key back to the open padlock position, before removing the key. You can expect a small amount of water to expel from the manifold. Then remove the key.
7. If you do find the water continuing to expel from the hole, this will be because the nut is not tightened enough.
8. If you find you have filled the boiler to the second bar, don’t worry. Simply go round your radiators and bleed them. You may find you have to repeat this process again.

If your boiler has an external filling hose or sometimes called a filling loop, then you need to follow the corresponding instructions. You MUST always switch the boiler off before pressurising any system.

1. Firstly you need to locate the filling hose and see if it is attached to both ends of the pipe (mains cold water to boiler pipe). Make sure both ends of the hose are attached to the valves properly. The hose should be located close to the boiler, and in most cases it is under the kitchen sink.
2. Depending on how the installer has chosen to install the filling hose, there may be a valve at either end or a valve at only one end.
3. Next we need to open the valve(s) to allow water to fill from our mains cold water to our heating system. You will be able to hear the water filling into the boiler. This tells us that the system if filling up.
4. Continue to fill your system until the gauge on the front of the boiler in at the required 1.5 in the green zone.
5. What you then need to do is isolate the valve(s). This ensures there is no more water entering the central heating system. What you don’t want to happen is for the needle to keep going up.
6. You then need to release the filling loop from the pipe. Expect a bit of water to come out of the loop, but if the water continues to come out you will then need to tighten the valve. If you exceed the green area on the pressure gauge you can simply bleed the radiators in your home and the pressure will go down.