My 550 is bone dry. I've cleaned the small in line screen blew out the line. How do I know if its the selinoid or humidistat?

Hello, sounds likemyou have either a bad humidistat or solenoid valve, disconnect the wires from the humidistat if this turns off the humidifier than replace the humidistat. If not the solenid valve will need to be replaced,

Do you hear the solenoid click. Furnace must be on and humidistat must be up. Do you have the ability to check for 24 volts (2 wires at solenoid). Loosen copper nut at solenoid to see if water is present. (Be careful about water spraying). Loosen nut on humidifier side of solenoid. Could be small blockage in copper line at solenoid.(There is a very small orifice there that could get clogged)
Could be Humidistat also. really need voltage meter to check wiring.

Of course make sure unit is plugged in and all fuses are good or reset. Here is the owners manual for all trouble shooting: hope this helps.
http://www.aprilaireparts.com/manuals/aprilaire-550-owners-manual.pdf

Turn off the water to the humidifier

Disconnect the water line to the inlet water valve (the solenoid), catch any excess water or drips in a small container

Turn the water back on slowly and see if water flows through the open line (the one you just disconnected - catch the water in a small bucket)

If you have water to the valve, it's probably the solenoid valve - you can test this by reconnecting the water line and turning the humidistat all the way up. You should hear a click as the solenoid tries to open. If it clicks and no water comes out it's the valve. If there is no water to the valve, you'll need to detrmine the reason(s). Sometimes the small line tap valves commonly used with humidifiers can plug up or malfunction. If you try to repair or replace the tap valve, make sure the water is turned off.

If no click, it could be the humidistat or there is no power to the unit.
If the humidistat is bad, you won't hear any click and no power will be sent to the solenoid valve. In that case, the humidistat may be defective.

Depending on your comfort level and knowledge, you can try applying power directly to the valve by bypassing the humidistat, but only try this if you are comfortable working with electricity. The voltage should be around 24 volts (in the USA) , which is low, but requires some knowledge.

1.yes you can service it yourself the 550 takes a number 10 pad I recomend the oem pads for there strength and durability. You need to clean the bottom tray of any lime scale I use a stainless scrunchie. the top tray has a sandy grit surface that should stay there, just clean away the lime scale. Then shut water valve off to the unit remove the incoming line from the solenoid valve and use a dental pick to remove the strainer,clean this out thouroughly of any debri and return it to its home and reconnect the line. Next go to the other side of the solenoid valve and remove the compression nut there blow on the tube to make sure the orifice is clear if not use a orifice drill the same size and clean it out. Return the tube and tighten the compression nut. If all nuts are tight turn water back on (if you have a needle valve which most people use even though there against code, you may need to tighten the packing nut) and check for leaks. Set humidistat till it clicks for testing(this is a manual type with numbers 15% to 45%) then turn on furnace. Depending upon which furnace you have some are tied into the circuit board others have a current sensing relay attached to a 24 volt transformer. You should here the solenoid thump when the furnace kicks in or blower starts. If not you need to check for voltage at the solenoid the 2 wires there will read 24 volts. If not you may have a faulty current sensing relay or other problems. If all work set humidistat to 35% and watch your relative humidity in the house. You may have to adjust as it gets cloder to a lower humidity

Have at it my fingers are cracked enough from cleaning humidifiers

Tinner
Sunsetmech

Have you checked to see if the solenoid opens and closes? You should hear a distinct click when the solenoid valve energizes. Depending on the quality of the water in your area, it's possible that the valve is scaled up....again and plugged. If the valve operates, you can usually clean it with a product called CLR which dissolves scale (lime buildup). This will require removal and disassembly of the valve. Please be sure to turn off the power before working on the unit.
Some solenoid valves are equipped with an inlet screen that could also be plugged with scale or debris.

Check and make sure the voltage is the correct - Usually 24 volts.

Almost every time one of these went out on me the wires were touching some part of the metal, or pinched somewhere. The easiest way to fix that is use a temporary wire and hook it up. Make sure you double check the voltage though. If you have a meter and know how to use it check for continuity between the wires for the humidifier

you should have a humidistat that should shut it off when set to zero. if the water solenoid is stuck, water will keep coming out even when the system is not heating. all humdifiers will have a water line ran to them. yours is most likely a 1/4"copper line that runs from the water solenoid on the side or bottom of the humidifier to a saddle valve on one of your water lines. this saddle valve is usually installed very close to the water heater. follow the line to the valve and shut the water off. sometimes you have to loosed the nut on the water valve to get it to turn easily. do not loosend the nut more the 1/4 turn and then make sure you tighten it back down after shutting the water off.

It could be that the humidistat is not calling for humidity. Make sure that you have the dial turned up all the way (as far as it will go, just to test it) and that the blower on the furnace is running - if the unit is properly wired, the water will not run unless the blower on the furnace is running. This should do the trick. If not, the only other thing would be a bad humidistat. Good Luck!

I WOULD CHECK TO SEE IF YOU HAVE ENOUGH V/A OUT-PUT ON TRANSFORMER. I DONT KNOW IF YOURS CAME WITH ITS OWN TRANSFORMER. IF IT DIDNT YOU SHOULD HAVE A MINIMUM OF A 40 V/A RATING STAMPED OR PRINTED ON THE EXISTING TRANSFORMER. IF THE TRANSFORMER IS EXTREAMLY HOT ... YOU MAY NEED A 75 V/A TRANSFORMER WITH THE SAME VOLTAGES. INCREASING THE V/A CANNOT DAMMAGE ANYTHING IT JUST GIVES YOU MORE POWER WHEN EXCESIVE CONTROLS AND WIRING ARE ADDED TO A HVAC LOW-VOLAGE (24v) CIRCUIT. IF YOU LIKE YOU CAN CALL ME AT 727-363-7071. I AM A RETIRED HVAC&R CONTRACTOR WITH 45 YEARS EXPERIENCE. I HATE THE NEW SENSORS THEY HAVE TO ACTIVATE THESE NEW HUMIDIFIERS. I USE TO WIRE THE HUMIDIFIER TRANSFORMER (SUPPLIED WITH HUMIDIFIER) TO THE LINE (110V) SIDE TO THE LOW SPEED ON YOUR BLOWER MOTOR. THAT WAY THE ONLY THING THAT INTERUPTS THE CICUIT IS THE HUMIDISTAT. YOU NEVER WANT THE HUMIDIFIER TO RUN IF YOUR SYSTEM IS NOT "CALLING FOR HEAT". NEVER TRY TO ENERGIZE THE WATER SOLENOID THROUGH YOUR HEAT WIRE(USUALLY SMALL THE WHITE WIRE) FROM THE THERMOSTAT. THIS WILL RESULT IN BURNING YOUR HEAT ANTICIPATOR OUT ON THE T-STAT.