I have a Weil McLain CG-4-SPDN boiler. It's been working great, up until today.

The standing pilot was on, but the boiler would not fire. Both zones were calling for heat. The transformer relay was buzzing loudly.

I jumpered the roll-out/spill-over switch, and the boiler fired.

I went and bought a new switch, installed it, and the unit worked for 15 minutes - the switch blew again.

I have confirmed that the electric damper is open. I have confirmed that the chimney flue is drawing (although the duct to the flue is black).

Any ideas as to what's going on? I realize that the flame is too high...

I have a boiler tech coming out tomorrow, was hoping to have some more insight before he gets here.

Thanks in advance,

Cary