I have an aprilaire model 6303 control panel, and the B and G terminal lights are on, on the equipment output and the fan runs continously. Is the board bad or what please help

SOURCE: Humidifier control .

if humidifier was wired into thermostat circuit for power instead of seperate transformer , this can happen. you need to see if you voltage going to the solenoid valve. if you do , and it isn't opening, the valve is bad . this is assuming that it is using a # 50 relay to come on only when the fan runs . . make sure the water valve is open

SOURCE: Aprilaire 600 - change water panel light stays on

Turn the control knob to the test/reset position untill the change water panel light blinks to reset the change panel timer. Make shure the furnace is running calling for heat.Turn control knob to prior setting after resetting timer. Hope this helps.

SOURCE: Water only runs with humidistat in test/reset mode

you need to make sure your humidity level in the house isnt higher then what your humidifier will provide at any givin outdoor temp. this chart is in the owners manual. you cant remove the wires going to the ODS or it will give an error unless you have a resistor to put in its place. Anyway if the humidifier works in test mode according to AA it works so you may have higher humidity than you think, the highest your gonna get is 45% as the temp outside drops it will allow less humidity so it doesnt cause window condinsation (property damage) here is a copy of the chart. the #s on the left are the dial setting
TABLE 2 – % Relative Humidity Guide
Outdoor Temperature (°F)
-10°F 0°F 10°F 20°F 30°F 40°F
1 10% 10% 10% 15% 20% 25%
2 10% 10% 15% 20% 25% 30%
3 10% 15% 20% 25% 30% 35%
4 15% 20% 25% 30% 35% 40%
5 20% 25% 30% 35% 40% 45%
6 25% 30% 35% 40% 45% 45%
7 30% 35% 40% 45% 45% 45%

SOURCE: no water flowing to water panel but have water to

To test solenoid, apply 24V directly to the terminals as see if water flows through it. Alternativly, turn everything on, ensure that there is 24 volts accross the solenoid wires, if you show 24Volts and no water, solenoid is bad. To test you will need to set your meter to AC Volts.
If you have a separate black transformer supplying the 24 volts, hook that directly to the solenoid. You may also be getting the 24Volts from your furnace circuit board, if that is the case you will see two terminals usually marked HUMIDIFIER on the furnace circuit board (you will need to open your furnace usually 4 screws or so.) There is 24 volts there WHEN THE HEAT IS ON , run two new wires from those terminals to the solinoid and see if it passes water cuz that is when those terminals have voltage. Best way is with a meter though and if you have 24 volts at the solenoid AND no water, it is bad. If NO VOLTS, then could be the the humidistat or a disconnected wire somewhere in the path.

SOURCE: Why two 24 Vac on aprilaire 700's control unit?

Okay, I looked up the installation manual online to see exactly what you are working with.
Yes the R anc C need to be hooked to the transformer supplied with the unit. The primary 120v side needs to be hooked into the power coming into the furnace. this can easily be done were the L and N get hooked into your furnace or circuit board on the furnace. This will provide the contiuous power to the unit. Preferably you will hook this after the door switch of the furnace so that you will kill the power toit if you take the blower door off.
The ODT terminals are for the outdoor sensor if you want to hook that up it will vary the humidiy in your home according to the outdoor temperature then.
Now the W/G and Cf terminals. If you have 24v coming from the HUM terminals of your furnace you DO NOT need a second transformer. You must check your furnace manual or check the voltage to them with the furnace blower energized. The HUM terminals will only have power to them when the blower should be running.
If the HUM terminals are 120v then you need to get another transformer and hook up the primary side to the HUM terminals so it is powered only when the the blower is running. Hook the secondary side to the W/G and Cf terminals.
So bottom line is that you need to figure out what voltage your furnace is giving to the HUM terminals and then go from there. Some times the EAC terminals or the ACC terminals will be 24v on the furnace board. Either of them could be used also, as they are only energized when the blower is running also.

Heatman101