HP printer not connecting to Wi-Fi with iMac

I have an HP printer with WiFi capability. I was set up for wireless printing to my iMac. the printer went off line yesterday and I have not been able to reconnect ti the WiFi. I have shut down the router, iMac and printer. I waited about 5 minutes and turned on the router, iMac and printer. The iMac recognized the printer but did not connect to it as the default printer. Any suggestions?