Arrived on site to customers home as he had no heat or hot water. Upon initial inspection of the boiler press the power button to wake system up and boiler began to fire. Went through fall history and found a delta T protection as if boiler had no flow for a small period of time 18 hours previous to my arrival. Checked all wiring and checked pump current draws. System was working as designed. It is believed that a small bubble of air was still stuck in piping and came free of current configurations and cavitated a pump for a brief moment. Called Tech Support and left a voicemail.