There is a small clip that holds the knob in place. It sounds like the clip may be missing, or the shaft on the switch is broken off, causing the knob not to stay in place. The part number for the clip is 688805. The push-to-start button part number is 3395385 (if required). You can view close up drawings of these parts at appliancepartspros.com. Just use the "Search by Part Number" feature.

There is an excellent exploded view diagram of the dryer console at searspartsdirect.com. Just type in the model number you provided as "110.66722694". Look under the "Top and Console" heading for items 4 (retaining clip) and 5 (push-to-start switch). NOTE: item 4 is misidentified under the description, but the part number is accurate.

The reason I'm referencing two separate sites is because the first site I mentioned offers better prices, but does not show any illustrations of your dryer model. They DO carry the part numbers, however, because these parts are the same on several different models. The second website shows all the illustrations. I apologize if this is confusing.

If you have questions, please post back and let me know. If you require additional assistance with replacing parts, also let me know. I hope you find this helpful.

I just took a look at your unit. Thanks for the model number. The knob when properly functioning, simply slides down over the shaft and should fit snuggly. Take a look at the back side of your knob and see if it is cracked. If it is, part number is 3402594 and your cost is around 55.00 in new or 27.00 in good quality used. Used would be cheaper obviously. Run a search engine for good quality used parts if looking for a used one. Good Luck, Eric Campion