We just had a contractor install a Moen valve in our bathroom remodel. It is a M-Pact common valve system and the model number is T2449pm. When I fill the bathtub with the bathtub spout water is dripping from the shower head. What are the possible reasons for this. I had one plumber come out and say that the valve was installed upside down. But the contractor has insisted that this is impossible. Who is telling the truth? PLEASE help!

It is possible to install a Moen upside down but a plumber would not make such a mistake. It would also not cause the problem you describe. I tend to think the plumber is the lesser knowable of the two in this situation. Usually a new valve will not dribble, old ones can. I would ask the contractor to remedy the situation in any case since you paid him to do it correctly. If the valve is faulty, very doubtful, it has a lifetime warranty from Moen. Moen;s customer service desk is available to answer repair question but I still think you should not have to do any of the work.

The diverter is on th tub spout of this model, right. Possible causes are partially block piping to tub spout, partially blocked spout, diverter valve not completely open, excessive water pressure.

Remove tub spout, It has a set screw under the bottom that you loosen and then pull spout off pipe.

Open shower valve and flush spout pipe. Does water come out shower head? If not check spout for partial blockage, and that diverter valve can be completely opened.

I agree with Bob and Harold, the first thing is to remove the spout and open the valve see if the water is dripping from the shower head, if it does then you need to ask the contractor to fix the problem as Bob says, if it doesn't drip then the problem is with the spout, proceed as Harold suggested, good luck.