I guess it depends if you don't mind buying a pump/motor, or want to dig into your old one. Most likely it's either a bad $8 capacitor or inertia switch. If there's a bump-up on the motor with a cover on it, remove it and check the capacitor. Make sure you discharge it by grounding the terminals together before touching it with your hands. Some capacitors are behind the back cover too. You might need to remove the motor/pump assembly to get at it. Type into youtube how to check motor capacitors. It's pretty easy. You have a couple other pumps so you might as well learn now anyway unless you just don't want to mess with them.
I've had them go on like air compressor motors and HVAC stuff. If that's all it is, then it's a cheap and easy fix, and they do go out. But if it's more than that, and you don't mind springing for a new pump/motor, that might not be a bad way to go either. Chances are the circ pump may spring a leak at the pump seal sometime in the next couple yrs anyway and since the impeller generally seizes onto the shaft and needs to be broken to replace the seal (and replaced for $35 + the cost of the rebuild kit) ...well by the time you do all this, the better way to go is to just buy a new assembly if your time is worth anything. But at first, I'd take a look at the start and/or run capacitors because that might be all it is.
If you do buy a new pump, I'd advocate buying one identical to what you have so you can use your old one as parts if the new one ever craps out just before company comes some Saturday at 5:00. Maybe come winter you'll have time to pull yours apart and fix whatever's wrong with it and have a spare.
