Hi Guys i have just finished plumbing my CH System an open vented oil fired sysem with 8 Rads the thing is when i switch it on there seems to be a gurgling sound where the return and flow pipes meet the manifold to send the water to the rads also should i have a cold feed running into the flow pipe to the boiler as i only have it going into the return sorry for all the questions at once but just want to make sure i have it all set up right oh and there seems to be air in the rads and they have to be bled a couple of times system is only up and running for 2 days