Hi, I have a 1960's American Standard boiler that has two zones, one of which is not heating. Can also hear water running so believe problem is that system needs to be purged? Read alot of info but none of set-ups seem to be same as mine so looking for advice before I attempt. Going to attach two pictures. One showing return and water supply, second the outlet and expansion tank setup. Just prior to hose bib and gate valve on return there is a TEE for two zones, each of these also have a small gate valve.