Okay - I'm also not sure I'll ever hit 165 f because right now we'd be running far less than that (like 100f). On outdoor reset but the curve is set to max out at 135. I believe there are models available with different temps.
After re-reading the manual I think we're talking about the same thing ("Tarm Biomass recommends the use of an additional Termovar valve model 6440AF (TV2) for most installations. Without TV2 it is possible that when a small zone is the only zone calling, a master bathroom zone for instance, all of the heat the boiler is producing is drawn to the small zone. The result is that a 100,000 – 175,000 Btu (30-50 kW) boiler is sending all of its output to 2,500 Btu (0.73 kW) load. The boiler could quickly reach operating temperature and shut off, which must be avoided. TV2 solves this problem. It operates much the same way that TV1 operates except that it is a divert- ing valve. Port 1 of TV2 receives water from the return manifold. Port 2 of TV2 is connected to the supply manifold. Port 3 of TV2 is connected to the return to the boiler and to the thermal storage system. When the TV2 senses water 165 oF (74 oC). and above, it shunts water from Port 1 to Port 2 (back to the supply manifold). Because water returning to the boiler from the return manifold is diminished, the remaining flow from the boiler is forced through the heating coils in the thermal storage system. The result is that both the zone and the thermal storage system receive hot water and the boiler may continue to burn with a demand equal to or greater than its output. The end result is that the heating load is always prioritized over the thermal storage system, but heat not used will be stored in the thermal storage system for later use".
So, what do we think, do I need it?