In the CB Install design illustration
http://centralboiler.com/media/2503/install-central-boiler-forced-air-system-c110.pdf, it shows a boiler drain on each side of the thermostatic valve sandwiched between two valves.
Do I assume this is so you can not only bleed the system but ensure the thermostatic on the heat exchanger side is getting water (meaning the thermostatic is working)?
Also provides a filling site for the lines as well.
In my design, I switched out the boiler drains with Webstone 1" Full Port Forged Brass Ball Valve w/ Hi-Flow Hose Drain & Reversible Handle, IPS Union x IPS #40434/50434. This wash cheaper and includes the unions so I can take out the Thermostatic Valve easily. This serves as both the inline valve and boiler drain in a combination part.
I also put in a Webstone 1" IPS Full Port Forged Brass Ball Valve with IPS Hole #41724 before the #40434 on the supply line so I can install a temperature gauge (tells me the loss from OWB). Didn't need the valve but this was the part I could find that included an IPS hole for a temperature gauge.
Probably should put unions inline on the outgoing to complete the Thermostatic valve removal option.
#41724
http://www.supplyhouse.com/sh/control/product/~product_id=41724#50434
http://www.supplyhouse.com/sh/control/product/~product_id=50434