How can I bleed air out of heater system ?

Mercedes 310d has air lock on heater,can anyone tell me how to get out to make heater work?
Cold mark, December 2016


done
Start the engine up until its getting warm NOT HOT then disconnect the heater hose from the bulkhead the top one and let the water come out until the air stops put the hose back on and that's it fixed...

william small, March 2017
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