If you have an Irritrol RD-nnnn key and it won’t open:
There’s usually a plastic key you turn on the side of the case to open it. While you turn it and keep it turned, pull on the door; they sometimes stick closed a bit.
Usually when this happens, it’s caused by the door having a fair bit of friction due to dust or dirt.
Try turning the key clockwise enough that you feel some resistance and give the door slow pull. If that doesn’t work, sometimes too much pulling pressure prevents the key mechanism from turning. Try pushing the door closed more and see if the key will then turn a little more and try pulling on the door again.
If you don’t have an Irritrol RainDial key:
(Also consider borrowing one from a neighbor to get in. You can usually buy them on Ebay for a few bucks or call Irritrol directly.) If those don’t work, read on.
If you don’t have a key, you can usually get into the case with a slot screw driver. It takes some patience, but you have two methods to emulate the key behavior. The key is just a star-shaped gear that connects with another gear to lift the plunger from the hole in the case door.
1) find a screw driver about as wide as the hole, put it in and rotate it clockwise, trying to catch the teeth of the mating gear like the key would.
2) put the screw driver in the hole at a 30-degree position (about 1:30 on an analog clock) with the blade horizontal to the ground and lever it downward to about 3:00). the goal is to slide the driver into the grove of the inner gear and lever it it upward.
Forcing it open will often break the catch on the case, or the square loop in the door that it catches. Many used timers I see have the inner door “loop” broken so it doesn’t catch any more. There’s usually a lot of friction around the door that can keep it shut without even needing the locking mechanism to work.
To get a new Rain Dial key:
Most local landscaping supply stores (not big-box stores like home depot, but more like the landscapers supply stores that just deal with landscaping). They should have them as well. Ebay typically has them for sale.
If not, you can contact www.Irritrol.com
– look for their customer service number and they may just send one to you for free.
I hope that helps,