We had problems with air getting in the system as well. We LOWERED our vacuum breaker and that worked (it is now on the return pipe about 3 feet below the panels which are on the 2nd story roof). We first had it opposite the input, then opposite the top return, neither worked. The installation manual for the Aquatherm panels we have then suggested the location we have now and it works great.
We cut a T into the return line about 16 feet up and attached the breaker there.
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