Combi Boiler Low Pressure

11 Jul 2009
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United Kingdom
Hi All,

We have a combi boiler for about 1.5 years now with no issues but now it is not heating the water at all. I noticed the the pressure gauge is at 0, when i switch power off and on again the pressure goes up to about 0.8 bar but then drops to 0. I read that combi's will not work if pressure not correct which I would guess would be about 1.

I have lots of valves underneath one marked "pressure Gauge" and one marked " filing loop" if I turn the filing loop nothing happens to the pressure and I can't seem to turn the pressure gauge one. There are about 3 other valves not marked and one is close to the filing loop one.

Any ideas how I get my pressure back up? Picture attached via google drive.

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You need to open both the blue handles to fill the boiler, open one fully and use the other one to control how fast you fill the boiler, make sure you switch both off when finished. you may need to open the black handle near the gauge, try filling and see if the gauge moves.
Opening both the blue valves should introduce water into the Domestic central heating circuit.
Once you pressurise, don't forget to bleed all radiators until all air has been vented out and pressure gauge is reading about 1.2 bar.

Thank you all, I was a bit unsure at first it was working but all radiators bled and pressure is about 1.6, probably was about 1.5 before, hot water seems to work now. I hope 1.6 wont be too high, but I will keep an eye on it over the next few days. I was advised to keep all rads on even if at 1. I was also told to sometimes set all rads to full now and again, would this be worth doing?

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1.6 bar should be fine, if the pressure increases, which it will do when the central heating is on you want avoid it from reaching much above 3 bar, as it will then start to blow out the pressure relief valve.
1.2 bar would be my choice setting. If the pressure does drop beneath the a certain level, usually around 0.7 bar the boiler will shut off and you will not get any hot water or heating.
I do not know what benefits there are of having all rads on or on at full?
I will keep an eye on the pressure when heating and water is on, is there a way to reduce the pressure. I think the advice about putting all rads on full is maybe an old wives tale someone told me.
To drop pressure when cold, go to highest located rad bleed valve, then draw a little water from bleed valve. Would not usually take much more than half a cup full to drop the pressure a enough.

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