We have a kenmore humidifier on the furance model # 48945. it doesn't stop running so our water bill is twice what it should be. I've tried to find a manuel on line so i can figure out how to turn it off. Any ideas (that doesn't involve smashing it, like my husband suggests)?

There could be several reasons why a humidifier stops running after refilling it with water. One of the most common reasons is that the humidifier's float switch is stuck in the "low water" position, which prevents the humidifier from turning on even after refilling it with water . Another reason could be that the humidifier's water level sensor is malfunctioning, which causes the humidifier to stop running even when there is enough water in the tank/

If you have a whole-house humidifier, it could be that the humidistat is set too low, which causes the humidifier to turn off even when there is enough water in the tank 1. Alternatively, if you have a portable humidifier, it could be that the unit's motor has burned out or that its fan has stopped working .

To troubleshoot this issue, you can try cleaning the float switch or replacing the water level sensor if they are damaged. If you have a whole-house humidifier, you can try adjusting the humidistat to a higher setting. If you have a portable humidifier, you can try replacing its motor or fan

There could be several reasons why a humidifier stops running after refilling it with water. One of the most common reasons is that the humidifier's float switch is stuck in the "low water" position, which prevents the humidifier from turning on even after refilling it with water . Another reason could be that the humidifier's water level sensor is malfunctioning, which causes the humidifier to stop running even when there is enough water in the tank/

If you have a whole-house humidifier, it could be that the humidistat is set too low, which causes the humidifier to turn off even when there is enough water in the tank 1. Alternatively, if you have a portable humidifier, it could be that the unit's motor has burned out or that its fan has stopped working .

To troubleshoot this issue, you can try cleaning the float switch or replacing the water level sensor if they are damaged. If you have a whole-house humidifier, you can try adjusting the humidistat to a higher setting. If you have a portable humidifier, you can try replacing its motor or fan

the Change Filter light is governed by reduced air flow. Check that both fans are running at full speed.

https://www.manualslib.com/manual/1022669/Kenmore-758-15420011.html?page=16#manual

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Mine would not turn on at all, found the contact pads for the buttons was corroded. Used an eraser and cleaned them, working good now. Of course the whole thing has to come apart to get to the contact pads.

Hello, no the humidifier should be running only when the blower motor is running. Sounds like the solenoid valve is faulty if water keeps drainig from humidifier.

Is this a small 3 or 5 amp fuse it is blowing at the furance. My assumption it is. If this fuse is blowing right away, then this is a direct short. The solinoid valve needs to be replaced. The valve has a direct ground to casing short. Replace the valve and the furance will not blow fuses anymore.

I think what your saying is the humidifier runs continuously. Check the wiring diagrams on the back page of the installation instructions.
You may have to install a sail switch to control the humidifier so that it only runs when the furnace blower runs (there are a couple of other ways to do this, but on older furances, this might be the easiest (it's the method I chose).

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

if it is set up right, you should be able to run your fan 100% of the time and the humidifier will come on when there is a need for humidity. you can experiment with leaving the fan on and see if this helps. it will run your electric bill up a little and also you will have a lot of waste water. that is a drawback to the bypass type humidifiers. also a factor is if the water supply is hooked up to the hot or cold side. it will humidify better on the hot side, but you tend to get more deposits that plug the solenoid over time and you will be running your water heater quite a bit. 1600 sqft may be pushing the limit of this humidifier.

Sounds to me like the solenoid valve is your problem and it is likely stuck due to sediment. I beleive Aprilaire has superceeded all of their old valves to the part number 4040 (used on all models of aprilaire humidifiers) - anyone who services these units regularly likely has one in stock usually $60 - 100.