Therm Under

I have a boiler in my condo. Had the heating guy out to service it a week ago because of a noise we were hearing - similar to the pilot on a stove but the clicking is faster and louder. He said it was fine and running efficiently and couldn't replicate the noise so we called it a day. Last night I was up all night with the clicking noise and when I finally went to check on it (my boiler closet scares me a little) there was a loud bang. One more bang followed closely after and another an hour or so later. There was a small pool of water under the boiler this morning when I checked. I have obviously turned off my heat and called the heating guy again but I was hoping for some diagnostic help before he arrives as they were a bit useless last time. Any thoughts?