I was checking our MCB Series Columbia boiler today in anticipation of a cold winter and noticed that the motor for the circulation pump was running, however neither the gas or electric start were operating. I verified I had continuity through both the "roll out" switch and the safety switch located below the flue. I then checked the voltage across the 24V feed from the control board to the Honeywell S8600M (Electric start & control for gas valve). I was only reading 5V so I took a closer look at the main relay/control board. I noticed in the 24v circuit, F1 (fuse) was open(blown). It did not look like a fuse-able link and it was not in any place that heat should be an issue. However, it did not appear to be a standard fuse either. It looked more like 1/4W axial resistor in a yellow plastic case. The marking was Buss 3A so I am guessing this is a standard fuse but designed to not be replaceable by the consumer, ect.... Anyway, I noticed that the connection for the wall mounted thermostat which was marked with a W had quite a bit of corrosion on it so I removed the board and cleaned all of the screw terminals with a Dremel. Nice and clean, I figured I had eliminated the excess load which had caused the fuse to blow, so I figured I would replace it. Since time is limited right now, I decided I would just solder some leads on a short 3A 125V glass fuse (used primarily for string lights) to fix the issue. Unfortunately, after mounting the board back in its housing and powering up the furnace, the fuse I installed blew as soon as it tried to kick on for the first time. I noticed that a least one of the traces coming from the plug for the damper motor passes through this fuse. Does anyone know if the damper motor would be a likely cause of this fuse blowing? Any other common causes?
Thanks in advance,