No/intermittent power to pressure switch

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.

Hello, if the transformer you got with the humidifier is one that plugs into a receptacle than all you need is either a current sensing relay or sail switch. First connect one wire to transformer then connect to humidiistat then to either sail switch or current sensing relay and back to other terminal on transformer. if you use a sail switch then it will mount in the return air duct if you use a current sensing relay it will cradle the blower motors common wire. I will post a pic of both current sensing relay

Sail switch

If you are not getting voltage to the solenoid valve then start at the transformer and check if you are getting 24 volts. If not then turn off power to the transformer and set your meter to continuity and check the transformer, if you dont have continuity the transformer is bad and must be replaced. If the transformer is good then check the wring to make sure the connections are tight and the humidistat, if that check out good then the current sensing relay/ sail switch is bad.

Hello, it depends on what type of setup you have with your humidifier. If you have a current sensing relay or sail switch than that wire connects there, howevere, if you have the humidifier that is powered by a furnace control board than that wire will connect to the transformer that the control board is providing with 120 volts with.

You need either a sail switch or current sensing relay to turn the humidifier on and off when the blower motor turns on. They both accomplish the same thing but in differant ways, a sail switch senses the airflow in the return air duct and a current sensing relay senses the current from the blower motor.

The system is 24 volt AC so start by checking the voltage from the transformer to make sure it is approximately 24 volts AC. The current will flow through the humidistat when continuity is made at the control as the humidistat senses that your house needs moisture. Disconnect the wires from the himidistat and set it to a high level, you should hear a click on the way up. With the 24 volt wires disconnected, check for continuity with a volt meter. If you don't have continuity replace it. Current also flows through an inductive sensor switch that hang on a wire from the blower. When the blower wire has current flowing through it, the switch senses that an closes makin the connection. With both wires disconnected from the 24 volts you can test for continuity when the blower is running. Overall, this is a continuous circle of wiring and is not directional like DC so think of the wiring a a big loop. The correct current has to flow through the transformer, through the humidistat, through the blower switch, through the solenoid completing the the circle before the solenoid will activate. Hope this helps.

The current sensing relay must be attached to the blower motors common wire to work properly, this is usually the white wire coming off the motor.

Is a digital Humidistat? if is not, it should click at some point, make sure when you test that the furnace fan is running and heat is on, then check condensation pump is not full. Also check the 2 wirenuts under the humidifier, another thing to check will be for the presence of a current sensing relay, for this you gonna have to open the furnace blower compartment and look for a 2''x1'' box with a U metal clamp, hanging from one of the wires that feed the blower, sometimes, relocating this relay fix the problem, You can bypass this device for testing.

The pressure switch is not allowing the igniter to heat up. Pressure switch is blocked or the flue is blocked. Take the draft fan off and inspect the flue. Also inspect the rubber hose connecting the fan and pressure switch make sure the ends are tight. Make sure the hose is clear and not restricted. And the pressure switch sometimes is position sensitive. I don't think it has been moved or anything. And very rarely do they go bad.

Have you changed the pad and cleaned it out ?