Hi I have just replaced 3 radiators down stairs one is not getting warm on investigation water is only coming in on one side aslso the connections I have made still drip even with plummers tape can anyone help. Thanks

water is only coming in on one side

That is normal. Water comes in one side and out the other to circulate.

the connections i have made still drip even with plummers tape

You will need to take the connection apart and check the threads for problems. OR you did not wrap enough tape on the fitting OR it has not been tightened correctly.

NOTE: the tape or pipe dope is not actually used to seal a fitting. The purpose of the tape and pipe dope is to lubricate the threads so you can tighten them easier for a leak proof joint.