I woke up three nights ago to the furnace blowing cold air. I have this problem once per year and I have to clean the flame sensor. This time though, I found a lot of water on the basement floor by the furnace. I cleaned the flame sensor and the furnace worked fine for about 4 hours then went out again. My thought initially was that because the furnace didn't ignite but the blower was running that the humidifier just kept dumping water but it wasn't evaporating so it leaked out of the cold air return where it connects to the furnace and then went on the floor.

I have an appliance service plan through Consumers Energy so they took care of the flame sensor. They put a new one. I shut the humidifier off for the last two days to dry up the water and to test the furnace. The furnace has been running fine. Now I'm wondering if something with the humidifier made the flame sensor go bad.

My question is this, if the blower on the furnace is running and there is no heat, will the water simply get blown from the filter into the cold air return then just dump out on the floor or is something else happening?

You did not mention what brand or type of humidifier you have. Most use an evaporator pad with hot water dripping onto the top edge of the pad. The water runs through the pad and out via a drain tube. The water should not be coming out of the humidifier even if the heat is off. First open you unit and check the pad and the water collection tray at the bottom. Also, test the drain hose by pouring water down it with a turkey baser or funnel. Frequently these units build up a great deal of lime and scale. The scale can plug the drain tube or cause water to wick over the edge of the pad and drain tray.

The humidifier is an Aprilaire 550 and the Furnace is an Amana. I believe both are for 1995 manufacturing date. This unit does use the pad. I replaced the pad today and turned it back on. I will see if it makes a difference.

Most Aprilaire pads are held in a plastic wrap around container of sorts. The top of the container has several water inlets that divert the water. The bottom of the containoer funnels the water to the drain tub. This enire container should be thoroughly cleaned whenever you replace the pad. I use a 50/50 mixture of warm water and vinegar. Soak it for about 10 minutes or buy some CLR.

Thanks for the advice on that. I ran water over the whole thing and scrubbed the bottom. There was a lot of build up on the bottom.

Don't bother to clean the water panel, they are quite cheap to replace. They come with a coating to help give the air a chance to evaporate the water held by this coating, otherwise its just like running water over a piece of aluminum.

We were not talking about cleaning the pad. You are correct, that should not be done. I was advising Alan6271 to clean the tray or plastic box the pad sits in. As you know, the diverter on top of that tray can become full of scale and it doesn't take much to start wicking water over the sides.