My 3 year old housebroken dog has suddenly started pooping in the house a couple of times a day. It is runny and light colored. What's wrong

Well... he is sick.:(
You need to bring him to a vet.
In the meantime I would suggest giving him bland food. When my dogs are sick I usually mix up plain white rice and plain chicken and then watch their stool.:eek:

Yes! Get him to the vet. It could be colitis or worse yet something with his liver. In which case the faster you take him in, the more of the possibility it can be fixed.