This client had a complaint that the boiler was working on and off. They stated that the thermostat was set for 72 degrees but never seemed to make it past 62 degrees. They tried bleeding the radiators, but that made no difference. They called me in to take a look and see if I could figure out what was going on. I checked the thermostat and it was operating properly. So, I went down to the boiler and checked the pump and water pressure. Both were within spec. As I was checking the pump, I could hear a constant “ticking” sound from the burner area. I removed the door to find the pilot lit but the sensor not sensing the flame. I also noticed something else, the pilot flame appeared to be very small. I shut the power to the boiler off and removed the pilot. I found a dirty flame sensor, but not too bad. I cleaned it and reinstalled it. While I had the pilot out, I blew through the pilot and was unable to get any air through it at all!
So, I pulled the pilot tube connection from the pilot off and exposed a completely blocked orifice and even the pilot tubing connector was blocked with carbon soot! (photo shown above) I cleaned it off with a wire brush and I paper clip end. I then blew through the tubing and the pilot to be sure it was clear and reinstalled the pilot and tubing. I restored the power and the boiler fired up perfectly with a nice, big, blue pilot flame. The “ticking” noise was also gone! The “ticking” was the sparker electrode repeatedly lighting the pilot because the sensor was not sensing the pilot flame.
This was causing the boiler to periodically light and sense a flame and other times, not sensing the flame. It was pure chance that the boiler would light at all and cause intermittent no heat.
Another issue could have been if the burner ground was not connected properly. If you have this issue, check all your connections and grounds.
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