Slow or slow-to-start fermentation can be due to faults in the process such as insufficient aeration which can be solved by rousing or increasing the rigour of the rousing of your wort.
Premature attemperation can be another cause, which can be solved by pitching more yeast, agitation or running hot liquor through the attemperator.
Another cause may be that the ambient temperature is too low, this can be rectified by running hot liquor through the attemperator or increasing ambient temperature using insulation, heating etc.
