Air lock after cylinder change??

7 Dec 2013
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United Kingdom
I’ve just DIY changed my hot water cylinder (indirect cylinder/ vented system) straight swap with identical cylinder and I’m struggling to get the heating and hot water to work together.

I select heating only on the controller and the radiators get hot but when I want to have heating and hot water I get neither. I’ve noticed the top pipe into the cylinder coil is hot but the bottom coil pipe is cold so I’m wondering if there’s an airlock in the coil?? Also the pump seems to be louder than normal making swishing noises.

So far I’ve closed all radiator valves and opened the heating drain valve and let it run for 10 mins (had a few splutters of air but nothing much) and while I was letting the water flow I have moved the 3 port valve to all positions to try and encourage it to flush the coil. Following that opened the rad valves and bled all of them starting downstairs. Then open the vent above the pump.

Thinking back on the hot pipe into the coil and cold pipe out I’m led to think there’s air in the coil.

What do the pro’s think about the coil airlock

And If so how best get rid of it??
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Can you bleed the pump? How about putting the speed up higher? That’s the limit of my knowledge, sorry!

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