You seriously need to bleed the thing properly before you do anything else, failure to do so will only keep you in a never ending loop of problems, just follow the instructions there is nothing difficult about it. Indeed once done your heater may then actually work!
Once you've successfully bled the system, you can bask in the inner glow of achievement.  
Until you do bleed the system, if you haven't already got head gasket problems, it will be a fair chance that it will become a self fore filling prophecy!

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