The first time I pushed that button, the whole check valve came flying out and landed on the ground. Lucky I noticed as I was able to reinstall it, although not without a lot of grief.
After the reinstallation, it continued to leak but I kept playing with it and eventually got it to operate properly.
I reread the instructions after experiencing all this and learned that after disconnecting the water supply and turning off the water pump I should have opened a tap to release the pressure in the system. It was the built up pressure that caused the button/check valve to blow out of the tube when I depressed it.
That was the one and only year that I ever depressed the button. Mind you, living in Vancouver, the temperatures never get really cold, but they do go down below freezing.