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boiler not pumping water to rads due to air

Postby billy bowen » Thu Nov 18, 2010 12:59 pm

Hi, i recently removed my hot water tank to move it 3 meters and replace all the loft water tanks with larger ones and pipe work between them, Gravity system, when i started the system up obviously loads of bubbles which eventually settled down but not fully. The heating was hit and miss the 1st couple of times then started working fine though could still hear bubbles going round the system, now the radiators are intermittent, usually after the heating has been on for a few hours they start to get warm, the hot water is fine and i can hear the boiler start up and the pump working but the pipes to the tank stay cold, i have bled the radiators 4 times but there isn't any air in them. My guess is that the pipes upto the tank are full of air which is preventing the water from reaching the tank, i have read loads on central heating bleeding but they dont seem to cover this. So what is the problem and how do i fix it?
billy bowen
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Simply Build It

Postby Perry525 » Thu Nov 18, 2010 7:56 pm

With central heating, the top of the heating coil in the hot water cylinder is often the highest point in the heating system.
I find adding an automatic air vent immediately outside the top pipe, will vent all bubbles.
Screwfix sell one with a compression fitting, you need the type that have a float and needle valve.
Just cut the pipe add a reducing "T" then the air vent.
Other than that, often there is an automatic vent inside the boiler, perhaps yours need adjusting?
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Postby eggers » Thu Nov 18, 2010 9:06 pm

it could be the pump maybe faulty, or cold feed may be blocked, but it probably is just one of those jobs that i would have to see before making a judgement
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Postby billy bowen » Fri Nov 19, 2010 1:34 pm

Hi and thanks for the replies, the pipe out of the top of the tank goes 1M horizontally to a T, the top pipe of the T goes to the water tank with an upside down U bend, does this work as the vent as the bubbles will always rise at this T junction?
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