No water coming out of the newly installed water heater. We had a plummer install a new water heater and after installation there was a bit of air which was drained out. Once the air drained out we had a bit of water then nothing. Turned off the taps for a bit and again water came out but stopped. Now no hot water at all. Any ideas..

First, this is the plumbers problem.
If you don't have hot water coming out it is because you don't have any cold water coming in.
Make sure the cold water input valve is open.
Do you have heat trap valves?

Open drain valve temporally, to see if you have water coming out under force?