Chop onion and celery (finely dice if you need to hide the veggies)and put in a 12 quart stock pot. (I double recipe and use a 16 quart stock pot). Add the chicken thighs, chicken broth, water, marjoram, and thyme.
Boil thighs until meat is completely cooked. Remove chicken and let cool.
Meanwhile, mix flour and milk together and add slowly to pot of broth stirring constantly.
When chicken is cool enough to handle, pull chicken into bite-sized pieces and return to pot. Add pasta (you can either cook it in the broth or separately and it could make soup cloudy).