A certificate and license issued under the provisions of this chapter is valid for only one year and expires on the thirty-first day of December of the year in which it was issued. The certificate must be renewed by the board upon application made within thirty days after the expiration thereof and on the payment of a sum not to exceed two hundred dollars for a master plumber’s certificate and license, and the sum of one hundred dollars for a journeyman plumber’s certificate and license. The board, when the condition of its fund permits and when in its judgment it is deemed advisable, may reduce the amount of the renewal fees, but it may not increase the same above the amount specified in this section. Any such change must be adopted by the board to take effect on the first day of January following its action and applies to all renewals in the classes specified in the ruling.