closed loop hot water

I have a oil fired boiler that I get domestic hot water and a hot water heat closed loop. To work on changing my pressure regulator,(a Watts 12-15 psi with a quick fill lever.) and my circulating pump; can I turn off my supply to pressure regulator and drain the closed loop while still allowing domestic hot water to operate. I do not know what the inside of the boiler is like; can the loop be drained of water, and the boiler be firing, with no damage to loop? Thanks.

Probably not. If it is setup with a primary/secondary loop, maybe. The boiler needs to be under pressure and the water lines full when it is firing or you'll get flash steam, and probably break something. If the primary loop can be isolated, then you could work on the secondary loop, but I'm not sure this is often setup to allow this.

I would say no but it depends on where your fill valve is piped into your system.

Usually they are near the expansion tank directly into the hydronic loop. I have a weird setup where I have a seperate tapping on my boiler where the auto-feed is plumbed seperate from the supply/return pipes.

In theory if I had a shutoff valve before and after it I would be able to do what you are asking about.

Not sure why your replacing yours but if you have one that is broken I've seen certain models that have union type fittings that allow you to replace the body/mechanism w/o any soldering.

Anytime I work on my boiler I flip the little red switch to cut power. I don't want to risk it firing in a non-normal condition.