Well, in the ongoing saga of trying to figure out why my HX is kettling, I found out today that the Delta T in the HX is probably normal. I had ordered a K type thermocouple to doublecheck my supply and return temps and lo-and-behold the thermocouple has confirmed that my storage tank temperature gauge that is on the bottom of the tank is off by a whopping 15-16 degrees !! I put a sensor probe on the outlet return pipe from the storage tank (which is right on the bottom of the tank) and one on the same line just before the boiler and they both read within 1 degree of each other. My temp gauge on the bottom of the tank was reading 162F and the thermocouples were reading 177-178F and my supply temp coming out of the boiler was reading 192F, so a 15 degree Delta T with a 400+F stack temp. And that was with the circulator on low speed. I still have the kettling going on, so now I'm even more confused than before !! LOL
Pat
Pat