I'm extremely new here so please let me know if I'm posting things at the wrong place. I recently (3 months ago) installed a new Trane 2 stage ECM furnace and along with it an Aprilaire 600 whole house Humidifier. It's upstate New York here, I've been setting the the thermostat to 73 degree, so furnace officially started working since late September.

The furnace and humidifier were installed by a local contractor.
I set the manual humidistat to 45% since the very beginning. And I have another small humidistat clipped right on one of the second floor registers where the hot air comes out. The humidity reading had been between 45% and 50% until about 2 weeks ago.

Two weeks ago the weather here really started to drop(ranging between 29 degree and 50 degree). And shortly after I started to feel air being dry at night. The humidity reading in the bedroom was somewhere around 33%. And when I put the humidistat right by the register(when the furnace is on and outputting hot air), it read 16%, that's what I was concerned about.

Here's the current information about the humidifier:

I hear the water flowing when the furnace is on, when I open it I see water in the distribution chamber and flowing through the four holes. I also see water flowing down the drain and feel hot air supply coming from the open damper.

I called the contractor company a few days ago, a service guy came in and said everything was fine, then he said my 4 inch air filter was plugged, therefore humidity couldn't go through. He charged me for a new air filter and a partial service call, because no faulty equipment was found, even though they told me the filter would last a year when they sold it to me. I was fine with everything if the problem was resolved, but the thing is, for the two days after the filter was replaced, the humidity reading by the register was still 16%. I actually personally went into a hardware store and bought a brand new water panel for the humidifier, still no improvement on humidity.

Me and my wife just had a baby 3 weeks ago and my wife had had this coughing problem for a long time, she feels much better when the air is not dry, so I was trying to give them the most comfort I can by getting the new furnace and humidifier. I'm not sure what kind of humidity level others feel good about, but we really hope we can get to around 45% here. Hope someone can help and sorry about the long post.