Heat on one side?

Just had radiator fushed at Local repair shop and now heat only comes out left side of vents. Repair man says their is nothing that he did that could cause this problem.
My heating system was fine before it went into repair garage. Can antone tell me what they did. Also temp gauge seems to be higher than when it went in Temp gauage never went above 1/4 but now is 1/2 up on the gauge. when driving on highway it went to 3/4 and I was getting worried that it would overheat.

Any help would be great.

Colin