Circulator pumps are the workhorse's of the hot water heating system. They quietly send that hot water to far away rooms. They automatically come on and off with only a slight nudge from a thermostat.
Circulator pumps run for years without a single blip, and then they just quit. They'll burn up quick once they go and a replacement motor will be in order.
Replacing a motor on a cartridge circulator pump is a pretty simple job, providing there are shut-off/isolation valves handily installed on both sides of the pump.
If valves to isolate the pump where never installed then you'll have to drain down the system make the repair and re-purge everything when you're done.
All of that takes time and another quicker way is to pull a vacuum on the system and make the repair without draining the system.
When leaks occur in circulator flanges, air can be drawn into the piping and cause problems over time. This air will sound like a river running through your home. Getting the air out can be quite a chore if you're not familiar with the procedure.
Purging a hot water heating system is an art you can master. Quieting down the air will also create savings in fuel consumption because the system will run much more efficiently.