I have a well with a pump and bladder tank. I replaced the check valve over the weekend. Last night we started getting a lot of air in the lines when we ran water and then the pump started running constantly. I switched off the breaker so I didn't damage the pump. This morning I flipped the breaker and the pump ran normally... but I still have air in the lines. Do I have a leak somewhere and it is sucking in air? Also, I have water to all sinks and showers, but the toilets will not fill after flushing.

Any help would be greatly appreciated!!

You say you have a well pump and I gather it is not a shallow well but over 100 feet in dept and you also have an expansion tank which the bladder depending on size of the tank should be the same pressure as your low setting.

If you pump runs constantly : a faulty limit switch (low-high pressure switch) or low water table or a leak in the line than runs down the well pipe or on the submersible pump ie: Jacuzzi or other brand, a leak on the unit.
A question? Do you have a filter on the inlet side before the water travels to your pipes or hot water?

Your assumptions are correct. The pump runs okay for awhile... although we have lots of air in the lines. Then after a few hours of normal water usage, it starts to run constantly.

It seems this all started after you installed the new checkvalve. Why did you replace the valve?

It might be that your water table has dropped to the point where the pump is pulling air and water... thus the air in the lines. As the pump continues to draw water, it eventually runs dry and thus continues running. At that point you would have very little in the way of water volume or pressure. When you turn the pump off, it is able to recover to the point where it once again can supply at least some water.

How far down is your pump?

We have a large amount of iron in our well, and we also have air from time to time. We clorinate ours, as to diminish the iron level, and it automatically reduces the air in the lines.

Call a well company and see what they say. They may give you some free advice.

It sounds that you could have a faulty submersible pump. I had a similar problem as the pump ran and ran and ran but I had low pressure. I found that my Jacuzzi had a faulty pump and was blowing water up the line but also out the side of the pump unit. I ended up removing my own pump (175 feet down) cut the unit off and replacing it with a new pump.