I have a large house with long plumbing runs necessitating a hot water circulation set up. I have a electric HWH with a dedicated return line plumbed to the drain cock at the base of the HWH. I have a small stainless steel circulation pump near the drain cock. One way check valves are installed at the cold supply line to the HWH and also at the drain cock. There is an expansion tank plumbed to the hot water supply exit using a "T" fitting.
I have the circulation pump wired with a 3 prong plug plugged into a digital timer to control when the pump circulates hot water. This way I can power the pump on a daily schedule. The circ pump is also wired to a "clamp on" aquastat activating the circ pump when the return line is <90 degrees and shutting the pump off when the return line temp reaches a fixed higher temperature (which I do not recall the temp off hand).
Everything functions as intended, except in the summer. The HWH return line/pump/aquastat is in an attic exposed to ambient air. In TX, attic temperatures easily reach 90-110 degrees. You're lucky to have attic temps near outdoor ambient temps which reach 100 for almost 4 months out of the year. (I have sufficient soffit/roof venting and a radiant barrier, so my attic temps are usually around outdoor ambient temps.)
My problem appears to be that the aquastat does not activate the pump in hot weather, because the stat/return line temp exposed in the attic is likely near ambient which can be at or over the stat's "on" temperature. When this happens we don't get hot water at the taps.
I have tried two different aquastats with different fixed on/off settings to no avail. I would just run the circ pump all day/night but I don't think the hot water supply or return line is insulated anywhere in the house, except where I have added insulation in exposed attic areas. I imagine running the circ pump all day until bedtime would increase the electric bill...
I have considered several options...just removing the aquastat in the summer, plumbing an adjustable aquastat with an immersion well, or designing some kind of "on demand" set up with wireless motion sensors (complicated). If anyone can provide any insight/advise it would be appreciated!!!