I have a Zoeller ejector pump installed in my basement pit. I have a Zoeller check valve installed about 20" above the pit cover. The pump cycles about every two hours without any toilet or sink use. I can hear liquid flowing in the pipe. The system is about 18 months old and it was professionally installed. The two hour cycling problems started about one month ago. Is the check valve leaking? Is this a normal problem?

Could be check valve but also could be leaking flush valve in a toilet somewhere.

Turn off water supply valve to toilets for a period, then check water level in tank. If water level has dropped flush valve is leaking causing ejector pump to activate.

You may be getting a back flow from an improperly installed connection to the main drain. The connection should be at least 45 degrees from plane to make sure it doesn't back into the new drain. That said, however, you may also have a bad check valve. You could also be getting in some ground drainage if there is a crack or hole in the sump basin. If you hear water flowing down the ejector outlet, you are getting flowback water from above.