Adding pressure to a system with zone valves

joeba

On a system with zone valves on the supply, and the circulator on the return(007 no internal check), do you have to open zone valves? I am assuming no, since the auto-feed has no idea if the zone valves are open or closed

Jamie Hall

No, you don't.

joeba

So I always like to know why. What happens if you do open them? Does it matter?

Alan (California Radiant) Forbes

If you add water with the zone valves closed, water will be added through the pump on the return as there is no check valve. 

If say, there is a flow check on the pump, the location of the fill valve in the system will determine the outcome. 

hot_rod

The additional water (pressure) will go somewhere- into the boiler, expansion tank, piping, etc.

Check the expansion tank pre-charge pressure before you add water and occasionally through the years. You need to isolate or remove the tank to do that.