I hope somebody may be able to give me some advice as to why my Eheim filter will not prime after changing the filter pad tonight. After pressing the suction aid so many times it just will not automatically fill with water as it should. I have repeated the procedure about six times tonight each time with the prefilter empty. I do get some air bubbles rising from pne of the suction pipes but it's just is not kicking into filling up, the filter is about six months old only. Any suggestions as to what I can try next please? Thanks in advance for any suggestions.