I have a Weil McLain CGM-4-P1 Series 9 105000 BTU per hour The unit will not shut off when then thermostat has reached temp. It continues to go until I kill the power. It did this once last winter but not again till this winter. I have elimated the thermostat because while it was calling for heat I undid the thermostat wires at the unit itself and it contined to function. The unit does buzz a little when calling for heat. I think it has to be the combination transformer-relay control center but before dropping money and time on that I wanted to get a second opinion. Anyone had these go bad and is there a way to test it? Much appreciated for any insight. Thanks!

I converted the tankless coil HW in my old (1975) American Standard oil fired boiler to a variation on indirect HW (with help from a friend who used do plumbing for a living). Reason was the coil wasn't producing HW rapidly enough, probably due to scale reducing heat transfer. I was going to put a new one in and was advised that some of the bolts were pretty rusted and it has happened that the boiler is damaged when trying to remove the old coil. The solution, although more expensive, was to add an insulated HW tank w/ a thermostatically controlled circulator that runs through the tankless coil. So I basically have a 40 gallon HW 'capacitor' which gives me enough HW. The set up has worked great for about 10 years but this morning I was running out of hot water. A hand on the coil output to tank was luke warm but is usually too hot to hold on for long. So it appears no circulation. Ass uming the tankless coil hasn't plugged, it can only be a problem with circulator or aquastat. Would my first step in trouble shooting be to bypass the aquastat and see if I get circulation?