Got a CH/HW system that is donkeys years old. Works OK, but the insulation around the water tank has always been crap - totally shredded red fiberglass+plastic jacket thing. So I pulled the jacket off to try to gain access to put some half-way effective insulation onto it. That's work in progress, but when I was removing the old jacket, a "bulb" from a thermostatic valve came twanging off the cylinder, and I'm not at all sure where to reposition it while I'm putting on the next section of insulation. The bulb connects to a thermostat valve, and I guess that when the valve closes, hot water from the back boiler is deflected up a pipe and back into an open header tank, past a bi-metal electrical thermostat, that I guess turns off the gas. Question is, should I re-attach the thermostat bulb at the top of the heated tank, or at the bottom, or at the mid-height of the heat-exchanger coil?
(My guess is, about half-way up the coil. But I could half-convince myself that it should be right at the bottom of the tank.)