Neil b in Heating & Air Conditioning
I have an Aprilaire 600a humidifier installed on my furnace. I can't get water to flow in at the highest setting, and it won't run in test mode either. The green light blinks, but nothing happens.. .

Are you sure you have water going into it?, does the Aprilaire 600 have a float that controls the flow of water? Is the float working? Is it possibly stuck?, if its not working now you can`t hurt it, so take off the cover and dive in

The manual: http://www.aprilaire.com/themes/aa/en/manuals/Owners_%20Manua_Model_400_%20500_%20600_%20700_100 06899.pdf

Has lots of informaton. Seems like the heart of the system is replaceable and should be done annually.

There you go,, there's the man with helpful information