I currently have a 25ish year old Weil McClain boiler. We have yet to use the heat up here in Maine(thankfully), so the boiler is only being used for DHW via tankless coil right now. I've noticed that the main hot water outlet coming out the top of the boiler is very hot, all the time.
There is a section of about 8 inches where the outdoor reset has a temperature sensor, then some type of black control box(that screws into the pipe). The pipe continues and has an outlet to the expansion tank, and then to the start of the baseboard. This pipe is very hot to the touch(150+) degrees all the way to the start of the baseboard. At the baseboard, some heat can be felt.
Any ideas on why this pipe(many meters of it) is hot when the heat has not been on for months?