Drained my boiler to flush it, then refilled. When the boiler was turned back on it would cycle on for about 10-15 seconds then cut off and the module would flash 'Recycle', minute later kick back on for another 10 seconds give or take. did this a few times, then i felt the circulator kick in on one of the recycles.....the boiler stopped recycling after a few times and now operates normal.

What would cause this after a refill?

Also my guage crapped out on me so I picked up one at home depot, got all the way back just to find out i need a 1/2 NPT not a 1/4....seems like all home depot had was 1/4"....are 1/4 more common?

Boiler is a Well Mclain Gold.