Aprilaire 560 humidifier, I have a problem with excessive water flow, this just started. The unit has always worked great. When furnace cylces and unit starts up you can hear the water flow, shortly after water will start draining out of the bottom of the furnace directly under the humidifier. The water is spewing inside the furnace and collecting in the tray of the "A" coil for the AC. The tray is very shallow the water then drips down and out the bottom. I disconnected the power to the Humidifier and the water leak stopped. I might add that (I think) , the water stops when furnance cyle is complete but not sure. By that time I am wipping water up from floor. Please note I have not changed any settings. The unit is like new, I have always maintained and cleaned.

SOURCE: Aprilair 760 Humidfier will not stop water flow to EV panel

If the water continues runs nonstop even when the heater is turned off, you might have either a bad solenoid valve or a bad humidistat. Simply disconnect one of the two low voltage wires going into the unit. If the water turns off then your problem is most likely your humidistat or the low voltage wiring. If the water continues to run even when the low voltage is disconnected you have a defective solenoid valve.
Good luck.......

SOURCE: Water is leaking from the bottom of the unit

The tune up kit that I ordered arrived on Friday and I installed most of it on Friday night. While it is nice to have a new frame and the distribution panel and I think the price of the whole kit was fair considering it comes with the parts and 2 water panels, the fix was really simple.

The kit came with the water distribution tube with with a new blue orifice (Aprilaire #4232) already inserted. This orifice is in the end of the plastic tube at the solenoid end. When I removed the old water distribution tube, the old orifice was not really dark blue anymore but kind of a light blue and was deteriorating from 12 years of exposure to the chemicals in the water. What should have been a pin-hole size opening in the orifice was up to about 2mm or a little more so the orifice was letting way too much water through.

If anyone else has this leaking problem, and your orifice is several years old, I would check that first. It is a $2.75 part and may be the cause of the leak. The whole feed tube kit is only $8.75 and includes the feed tube, nozzle, orifice, ferule, compression nut, strainer so if you need to replace the orifice, I would order the whole feed tube kit for a little bit more.

Hope this helps,
Roger...

SOURCE: water keeps running into humidifier even furnance blower is not

This sounds like, the 550 transformer is not connected to the blower motor power connection (in parallel)

SOURCE: Water flow from humidifier never stops. Even when furnace is off.

No, it will not stop flowwing if it is the water supply. A solenoid valve opens the flow everytime there is a call for humidity, but it stops at the humidifier when there is no call, so it will leak from that point until it is fixed or tightened.

SOURCE: aprilaire 600 humidier: water continuously runs

sounds like you may have it wired to a continuous power source vs one that shuts off with the furnace. The most common wiring is red to C & white to W