Hello. Thank you for your inquiry.
The reason that your treadmill is tripping the breaker is because you are experiencing "belt-to-deck friction." In other words, your walking belt (the belt that you walk on) and the walk deck mylar (plastic sheath attached to the wooden plank that the belt rolls over--look underneath the walk belt) are both worn out. There is nothing that you have done wrong nor is the treadmill defective. This is something that happens to all treadmills over time regardless of the price range, model, or brand. Think of it as the "tires" on your car going completely bald, from so much wear.
So you essentially have a bare piece of wood rubbing on a worn piece of plastic(mylar sheath). This causes the belt do drag. The treadmill automatically pulls more power from your wall, to compensate. Therefore, your breaker goes out.
The only way to prevent this (and it is necessary, because your treadmill controller could burn out next), is to essentially replace the "tires." In other words, a new walk belt and a new mylar fix kit (luckily for you you don't need a new walk deck---only the mylar kit--cheaper). If you can install them yourself, you'd be golden. If you have to get them installed, it'll run you about $120 plus the cost of the parts.
Here are the parts you need, and where to get them. This way, you can compare the price of repair vs, the price of a new one. My honest opinion, the older units are high quality units. The ones made 5 years and newer (proform) are junk, I would repair it if I was you.
Thank you for your information and opinion. I know that to replace the treadmill with a comparable model would be very expensive. Do you know for sure that the two items you reference are compatible with my model?
I most definitely know. I looked up your model through the manufacturer's website (ICONFITNESS.com). . .(they are the manufacturer of Proform units). I work on proforms, nordic tracks, weiders, weslos, end many others made by this manufacturer on a daily basis. For better peace of mind, let me guide you on what I did to get to the parts list for your unit.
1) Click on the manufacturer's parts website below: http://www.iconservice.com/CustomerService/parts.do
2) Under model name (not model number), type your model : 730CS
3) Decide on the version number of your treadmill (your model number label will say: 29927.0, .1, or .2---you click on 299270, 71, or 72 (you get the picture).
4) This will bring up the parts list for your treadmill.
5) Look at item #55 of the list. . .that is the walking belt. Two items after #118 is the mylar fixkit (that is the plastic sheet that goes underneath your walk belt, but on the surface of the walk deck). .. take a look, by pulling up on the walk belt. . you'll see it. That gets replaced sometimes. . it does wear. This helps you in that you do not have to replace the whole deck , which is listed at what? $165? so the mylar fix kit is the cheap way to go.
I hope this helps with your doubts. Regards, XXXXX XXXXX luck.