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How to pressurize a combi boiler

Boiler repair can be very expensive so control its  pressure.

If there is no pressure in the central heating system your boiler can switch off. Not working boiler means no heating and no hot water so how to fix it quickly? Here is the short guide which our engineers hope will help you to top up the pressure on your boiler, avoid boiler repair and know a bit more about it.

First, you have to think why there is not enough pressure. Did you bleed your radiators recently? If so you need to top up your central heating system. Did you have any pipework alternations done? As because of that boiler could be depressurized too. Also which is a very common thing there can be a leak on heating installation which causing losing pressure on the boiler. Leak from central heating installation in many cases can be very easy to fix, but also may be very big inconvinience for home owner.For example, if there is a leak on the ground floor under your sub floor you can’t see it. Is very difficult to find. Very often all ground floor have to be lifted up to investigate where is a burst pipe or hole in it. All this become very expensive.

If the leak would be located between ground and first floor you would notice water marks on the ceiling, walls or there would be just water dripping.

If the pressure goes down occasionally, say once a year and needs topping up that’s normal.

Ussually it should be between 1,2-1,5 bar when boiler is cold.

Some of the boilers have their internal integrated filling loop. The other have an external filling hose located normally somewhere on pipework.
For either methods of refilling you must remember to insulate the boiler and turn the power off.
If your boiler have an internal filling loop often there is a key attached to the tray under the apliance. Usually Worcester Bosh have a key for topping up the pressure. Carefully remove the tray from bottom of the boiler and locate manifold/filling loop into which you have to put the key. You need to find a mark or arrow on the key. This will show you lock and unlock position marked on the filling loop. If you already inserted and locked filling key you need to find plastic nut just next to the inserted key and turn it anticlockwise.
You done it? Good, so now concentrate on the boiler pressure gauge as you should see pressure increasing on it. As soon the gauge arrow will be in green position and pressure is about 1,5bar tighten the nut. It should sound like the water stop flowing into the boiler. Turn the key back to the open position and remove it from the socket. If you can see the water dripping from the key point that means you didn’t tighten the nut properly. If the gauge or display on the boiler showing 2 bar instead of 1,5 don’t worry. Simply find radiator easy to get to and bleed it a little bit. This will cause pressure to go down again. You may need to repeat filling in process.

If your combination boiler don’t have integrated filling loop it should be located on the pipework. It must be on cold water and central heating return pipe. Common location is on the pipes under the boiler however can be under the sink or different kitchen cabinet.

Again insulate the appliance from electricity. Simply switch it off.

Locate filling hose on installation and make sure is properly connected to the valves on both ends and is tight. One valve may be non return valve and second our filling valve. Next you have to do is open this valve to let the water fill in the heating system. While doing it observe the pressure gauge. This should show pressure increasing. Again it should be 1,5 bar (green zone). If it is quickly insulate the valves. This ensures there is no more water flowing to your central heating system. To confirm that simply remove the hose from the valves. Expect a bit of water is still in the hose so you will need something to catch it. If you done it turn the boiler on.

Hopefully above instructions will help you to get your heating working correctly. However if you don’t feel confident with this, or you are in need of boiler repair contact us today. We are heating engineers in Hertfordshire happy to help with all central heating issues.

Read more about boiler repair here

Here is our short video how to fill up Vaillant boiler.

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