Switch – Is an air pressure switch required for a whole house humidifier

There's two ways to wire this up. The first method is to take advantage of the HUM terminal on the furnace control board. This terminal will supply 120 volts when the furnace is running in heat mode, so you'll have to use an additional transformer.

You'll hook the primary side of the transformer to the HUM, and Neutral terminals in the furnace. Then you'll connect the 24VAC terminals of the humidistat, to the secondary of the transformer.

The other method, is to use the furnaces transformer to provide power to the humidistat. However, you'll have to make sure the transformer is large enough to supply the load.

With this setup, you'll connect the 24VAC terminals of the humidistat to the C and W terminals on the furnace control board. That way when the thermostat calls for heat, the humidistat will be powered by the furnaces transformer.

I can only provide anecdotal answers to questions 2 & 3.

2. I have successfully used a few drops of concentrated food coloring, at different places I suspect for leaks in a water softener and its related valves and plumbing. I used 3 different colors if memory serves me right. We had a very slow/unnoticeable leak, apart from the puddle of course. I was able to determine which valve is was based on the color dye that showed up in the leak (blue in this case).

3. The failed water softener in this case did fail due to high water pressure. I would see if there is any manufacturers rating for the humidifier's working water pressure. There is no telling what parts, valves or plumbing inside the unit make be deforming/failing under such high pressure.

Good luck in your troubleshooting and fix.