Air lock

[lazybone]

I had to change my water heater and I'm having trouble clearing the air from the line.  I've drained the coolant more than a few times over the years but I've never had this much difficulty.  I'm thinking I have to disconnect the hoses at the engine that go to the WH ? but then what?

[Ron Hill]

Ciao : Look in WiKi for the "burping" procedure.

Just disconnect both of the engine coolant lines to the water heater.  Then fill coolant into the one line until it come out the other - that should clear and air bubble in the WH out. 
Then reconnect the lines and run the engine.  You might even have to open the butterfly valve on the top of the thermostat to let more air come out until coolant starts to come out.  Then close the butterfly valve.

A thought 

[lazybone]

Thanks Ron, followed your advice.  Worked a charm.