Wire Honeywell HE220 to N8MPN/L, *8MPN/L furnace control board

It sounds like the wiring for the humidifier may not be correct. The solenoid valve, which controls the flow of water to the humidifier, should be wired to the humidistat and the transformer, not to the furnace or fan. It is possible that the bottom wire of the solenoid is connected to the wrong terminal on the transformer or humidistat, or that the top wire is connected to the wrong terminal on the humidistat. I recommend consulting the installation instructions for your specific humidifier model, or consulting a professional HVAC technician to verify the correct wiring.

I would think it would need to switch on & off to control the water flow through for correct humidity..

Honeywell is a controls company and makes a variety of auto-pilots. If this is a no spark problem,does the lead from the igniter go to a big PC board or a module. If a module, check voltage to the spark module or thermostat voltage to the ignition module. If it comes from a large board, the board may be bad. I'll need more Info. if this does not cover it for you.

Try removing the cover, and manually cycling on the controler switch? Does the solenoid click on, next to the humidifier (the unit with the water line running through it, with wires coming out of it)? If it does click on, is water running down the water pad? It doesn't necessarily drain water when it's working correctly. All of the water SHOULD be getting evaporated into the air return duct.

If it's clicking on, but no water is running out, you should check the water supply saddle valve and make sure it wasn't turned off during servicing.

If it's not clicking on, you should test that you are getting voltage (12v-18v DC) to the solenoid. If you're not, check all wiring connections and make sure they're tight. If you still don't get power, you have either a problem with your control unit/humidistat, your DC power supply, or the control board on your furnace. You may need to call a HVAC technician at that point, depending on your comfort level/skill level in that regard.

When you say the solenoid "stays hot" do you mean it's physically hot to the touch? Hotter than the water lines running into it?

If the solenoid is getting hot, it probably has a bad coil, and if you continue to operate it, you will probably burn up your DC power supply.

If you're getting voltage, you have water pressure, and the solenoid is still not opening, replace the solenoid.

Most of the humidifiers are run by 24 volts AC. disconnect the power wire to stat on circuit board and check there with meter and connect to low voltage ground for 24 volts, I'm assuming the two wires that power the humidistat are red and white.typically red is used for power. most likely you have power if the red for the stat is connected to the W on the board and the heat works, but the humidifier only works while heat is on.the next thing in line is the humidistat , it's a switch so if there is only two wires going to it take them off the stat and connect together, if furnace is on heat and running and stat wires are connected it will send power to water solenoid, if its not working yet the problem lies in the water solenoid if you have 24 volts at the two wires at solenoid.check while disconnected, do not connect those two wires together or a 3 amp fuse will blow on the furnace board. if you have 24 volts there then the valve may be bad or the valve may be stuck or clogged, loosen water supply line to make sure water is getting to valve. I spent many years working in the HVAC industry.

Not sure how much this will help you, but here is a link in pdf format to the Installation Manual, if you don't have one http://www.honeywellcentral.com/ssi/pdf/honeywell-commercial/HE220-Installation.pdf

If all else fails here is a number for Honeywell. Ask for Technical Support. (877) 841-2840

Honeywell tech support is awesome here in Minneapolis, I think you need seperate humidistats but check with HW, number is in owners manual.

it is best to use a seperate transformer for the hummidifier, but in some cases you can use the low voltage t-stat wire that runs your furnace, you will need to have one wire run to common, and the other to the heating side of your low voltage, normally its the red wire hooked to the w circuit of your terminal board, if you do decide to go with an extra transformer, make sure you you have it wired to bring on the humidifier only when the unit calls for heat, hope that helps

You can try installing the water line to your hot water if it is installed on cold line for more humidification. You should make sure your humidistat is up line 6" @least from humidifier for proper humidification measurement.

See if you have a screw marked EAC This to power an Electronic Air Cleaner unlike the HUM it also gets 120VAC only when the fan comes on. Not sure what make of furnace you have but if your heat is working OK don'tn change the control board the can be very expensive. there are other ways to wire humidifiers without using the HUN screw