the bungs should work ok if they go in well give it a try. bung it and drain water from a drain cock somewhere and see if it comes to a stop that will be a good sign that your system will bung ok
sounds to me like the pump is either not working or u have an airlock preventing circulation. the nooise u are hearing is the system pumping over because it has gotten too hot. with the pump running unsrew the front cap and see if it is spinning inside also bleen the systtem out .
I have just installed a worcester junior 28i into my mates dads place replacing an old glowworm fully pumped 'Y' plan system. the problem is the hw pressure is poor it comes out well when the tap is first opened but gradually reduces to a very poor flow rate with 10 -15secs.(this is the same on...