I have a GA92-100 EI Vaillant free standing boiler. It stopped running, so I read the restart proceedure. Turned it off, turned both (have 2) thermostats off, waited 5 min. and turned it back on, then turned the thermostats back up. It took a couple of minutes, but fired up. It ran until the boiler said 190 degrees then shut off with the pump still running. It cooled down to about 175 and I heard a click, not loud, but noticeable. I thought that it was going to fire the boiler again, but nothing happened. I think I heard a faint hiss of gas after the click, but not sure. I let it go until it was down to about 100 degrees. Tried to reset it again, but no fire. The power box on the front turned the pump on and began to hum pretty good. Thats it. I am leaning toward the ignition, but that doesn't explain the humming.