Position and purpose of Valve

robertsonje

What is the purposed of this valve in the picture? (The Shut Valve) Is shut the normal position?
Thanks.

STEVEusaPA

It’s for manual bypass. It’s to mix a little hot boiler water with the cool return water to bring it’s temperature up to help prevent condensation in the boiler.
Completely closed it does nothing. Completely open your house will never warm up.
It’s the worse way and not the best choice of valve to protect the boiler. You, or someone will have to figure out how far to open it to find the sweet spot.
And as time goes by and wire drawing starts to ruin the valve you’ll have to adjust it again.

hot_rod

What type of heat emitters do you have? If it is low mass like fin tube baseboard or air coils, it may be fine closed. Or if the boiler is oversized for the load.
To know, measure the temperature coming back to the boiler on the first, cold start up, all zones running. Within 10 minutes that return should be around 130F.

mattmia2

What is gong on with that vent connection?