combi boiler

How do you turn up the water pressure in a combi boiler – combi boilers are often installed in sealed systems and these can loose water pressure through normal operation.  As a result the home owner might need to tinker with the filling inlet and repressurise the combi boiler so that it can operate correctly.

A recent commenter said “My combi boiler’s stopped working, I know its due the water pressure being too low. I tried connecting a silver pipe to two copper pipes with black and blue valves on them, I turned on one of them hoping for a result and I got nothing apart from a drenched carpet.
Does anyone know how to get the water pressure back up again? ”

If you are in this situation its time to get our the boiler manual and look at the water pressure section.  If you are not confident you should consider bringing in a local or trusted plumber to help you.


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The typical combi boiler installation will have a filling loop. You will need to identify this and open the valves in the order indicated monitoring the water pressure indicator at the same time to ensure that the internal pressure does not exceed the recommended level.

Remember a qualified plumber can help here and, if you watch what he does, you will learn how to turn up the water pressure in a combi boiler so that you can tackle this task the next time it is required.



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    6 Responses to “How do you turn up the water pressure in a combi boiler?”

    • Octavio 139 says:

      under the boiler there should be twe taps usually white turn the bottom one on first then the other one the pressure gage should start to rise let it rise to about three bars

    • Beckett Grace says:

      Mine has a black tap that you turn and the water pressure dial goes up.
      Whatever tyou did with the pipes – i think you should put them back how they were.

    • Yael 33 says:

      either turn the valve (usually somewhere under the boiler) on for a moment or two/ call the helpline for the make of boiler it is/ use the internet to find the instructions for your make of boiler or if all else fails call a plumber!

    • Addison Whitaker says:

      there are two taps, but it’s possible that they might be obscured by the cornicing or hoarding that covers the pipes… I had to turn my taps to increase the water pressure. Couldn’t find these taps anywhere, so ended up calling the engineer… only for him to simply remove the wooden skirting which was concealing the pipes, and Lo! there were the taps!!

    • Adriel Morrissey says:

      If these taps are definitely to do with the heating system and not washing machine taps then open both when you have the hose connected Just do it slowly then you will see if it is leaking. charge the system up to 1 to 1.5 bar on the gauge, close taps and switch boiler on.

    • Drake Walton says:

      Although they may vary combi-boilers usually have a hose from the cold water supply in (mesh hose) which you then attach to the heating return (screw on to the tap). Open both taps (valves). This will increase the water pressure. When the water flow ceases to increase pressure, turn off both taps and unscrew from the heating return (you will get some drips from the hose so place a cloth/newspaper underneath). The gauge should be minimum 1.5 bar.

      I have to do this on a regular basis in the winter (central heating). It is important though that you disconnect the hose each time you bring to pressure.

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