CH cold water feed

[jimmir]

I've just joined the forum to ask what is probably a basic question for heating engineers. I've had a new boiler fitted and system powerflushed but although there is hot water and rads get hot I've got problems with air in the system which is nearly 40 years old. It's an open vent Y plan and the existing vent is near the boiler on the suction side of pump with the cold feed to the flow to the hot water tank coil and I think this is giving problems. The current recommendation is that the vent and cold feed should be close together on the inlet to the pump so I want to alter the pipework which is easy to do. The Glow-worm pipe layout clearly shows the cold feed joining under the pipe to the pump and this is also stated on this website http://www.gasman.fsbusiness.co.uk/system_basics.htm
Near the bottom of the page below the pipework picture it says this:
"the first connection is the 22mm expansion which rises vertically, then is the 15mm cold feed which enters from the underside"
I can do this ok but would like to know why so any comments appreciated.

 

[denso13]

It enters from the bottom to stop "parasitic circulation", or to stop hot water going up the feed pipe. That's the theory anyway

 

[Terry lambert]

Air is almost certainly being drawn in to the system through the open vent.

You could do a combined feed and vent ( cap the cold feed and make the 22 mm open vent a 22 mm cold feed)

You then have a semi sealed system, check in the Manu instructions that this configuration is okay with this boiler, from memory it's fine. It's much less likely to intrain air in to the system

 

[jimmir]

Thanks for replies guys - both appreciated.