Boiler almost done - 2 questions

[LegendsCreekFarm]

With the help of everyone here at this forum, I believe I will fire up my  CB 6048 for the first time on Saturday.  I did all the pluming up to the wrap around, after the heat exchanger. I have a friend who is a licensed plumber coming on Friday to do the connections to my forced water oil boiler. I didn't feel comfortable tapping into it myself so he and I are finishing it on Friday.

I will move on to my guest house which is the exact same set up as my main house so it should be a breeze, but I am wondering if I absolutely must have a thermostatic valve installed?  Central Boiler says that it must be installed on all 3 buildings but wouldn't the one I have on my main house be enough?  I believe the whole purpose of it is to send the water back if its not hot enough, correct?   Which leads to my next question.

If something happens and I am unable to keep adding wood to my central boiler, will the main house pump and heat exchanger work in reverse, to keep the central boiler water hot, using the oil that my main house boiler is burning to heat with?   It makes sense to me that my home oil boiler would fire up and send the hot water back to the central boiler, and I really hope that is the case.  I don't leave home often but you never know in an emergency.

[Holmes]

 Mixing valves often are installed to increase the water temp going back to the boiler so that the boiler does not get a thermal shock from cold water entering the hot boiler.  I have not seen a schematic on piping the boiler, so I do not know why central wants the mixing valves..  If it is for thermal shock then I would suggest you install them, it could void your warranty. But we all know outdoor wood boilers never spring a leak.   ;)