My iMac "forgets" my printer

Stranger than strange!

- New iMac (purchased Apr 2015) with Yosemite version 10.10.3
- New Brother MFC- 8910DW (multifunction) setup wireless with no physical connection to either the router or any computers. Verified on Brother website to be compatible with Yosemite.

Used installation disk for my three Windows 7 64-bit computers. Everything works seamlessly.

The installation DVD was too outdated for Yosemite, so both the printer and scanner drivers were downloaded from Brother's website.

PROBLEM: My iMac will only find the printer/scanner for about 15 minutes. To use it after 15 minutes, I need to reboot my iMac to get another 15 minutes use.

Apple support was great and spent a good deal of time helping me to resolve this problem. However, in the end they remain as baffled as I am.

Brother support sucked. Their "troubleshooting" resulted in finding my printer, but not my scanner for 15 minutes. In typical "It's not my fault" fashion, they simply blamed the problem on Apple and hung up.

No thanks to Brother's support, I got my iMac to access both the printer and scanner, but only for 15 minutes.

Any ideas?

For troubleshooting, go to the router's setup web page and give your printer a fixed IP address. You may need to do a test page printout from the printer - to know its MAC (media access) address for this. Set the printer in the correct subnet, but outside the DHCP range.
Example: DHCP range 192.168.1.10-40, set the printer at 192.168.1.99.

On your Mac, Add the printer using IP > HP jetdirect protocol instead of Bonjour (automatic locating protocol). You may need to change setup on Windows (at least for new IP address). My preferred protocol, HP Jetdirect, is known as raw port 9100 on Windows.

Thanks for the reply. I knew I'd forget to mention valuable info.

I had already assigned a static IP address to the printer. When I used the IP protocol, I could access the printer, but not the scanner (for some strange reason). As I recall, it still only lasted about 15 minutes.

Using Bonjour was the only way I (and the Apple rep) could find to use both the printer and scanner.

Did you go through the setup guide procedure for using it via wireless, and often setup at the printer or AIO itself and buttons and display. See the wireless setup section here if you don't have your own copy:
http://download.brother.com/welcome/doc002956/cv_mfc8910dw_use_qsg_lx9911001.pdf

Yes, I followed this guide completely except installing the MFL-Pro Suite. As I mentioned, during the installation it gave me an error that my OS version was too new so it wouldn't install.

The funny part I failed to mention is this MFC-8910DW is a replacement for our MFC-8680DN that died last month. While it was wired to the router, my Mac accessed it for 4-5 years wirelessly. The specs on these two units is nearly identical BUT the older unit installed on my Mac via the included installation disk.

While Brother has the drivers on-line, I can't help but wonder if their failure to make a Mac version of the MFL-Pro Suite available on-line that is creating the problem.