We had a problem with the humidifier in our central heating system. No humidity. Simply no water getting into the humidifier.
We called our trusted longtime HVAC engineer - Andy -  and made an appointment for a checkup.
At the appointed time, Andy was sick and sent a young man who was filling in for the day.
After an analysis, we were told that we needed to replace the solenoid valve which wasn’t letting any water in to the humidifier.
“Andy will call you “
After a day or two, I called Andy about the replacement.
“Let me come and take a look.”
So, Andy - feeling better - came over with his nephew to “take a look”. He did his thing, announced that the solenoid valve was fine, disconnected the little water hose and asked his nephew to go out to the truck and blow out the hose with the air compressor.
Back in a minute. The hose reconnected. The speck of debris that had clogged the hose was gone and the water flowed.
“I had a feeling,” said Andy, “and wanted to check it myself. Sorry it took so long.”
“Experience” I said to myself as I thanked him.