I moved into a new home 2 years ago and since moving in my 12 year old chihuahua
Started urinating in the house even though I have installed a doggie door. Why?

Why is my 12 year old chihuahua urinating in the house even though she has a doggie door and was previously house broken?

There are lots of reasons a housebroken dog can start having accidents in the house. Some as serious as kidney and bladder infections to diabetes, and some not as serious as a behavioral issue.

Is she peeing in the same spot each day? If so, invest in an industrial strength cleaning solutions, such as "Simple Solution" or Hartz pet stain and odor remover. You can also try mixing a solution of water and vinegar and thoroughly scrubbing the area. Is she doing this once or twice or all day long?

You may have to start from the beginning again, and act as if she were a puppy and re train. Every time she eats or drinks take her out side, when she does her business praise and reward. You may have to physically take her out and stand out there with her until she remembers what she is supposed to do.

When was the last time she was at the vet for a check up? 12 years is getting up there in doggy years, could even be the beginning of incontinence. Senior dogs and prone to memory lapses and trying to get away with things they once knew they would never get away with.