22.—(1) Where a person carries out work in relation to any installation pipework which might affect the gastightness of any part of it, he shall immediately thereafter ensure that—
(a)that part is adequately tested to verify that it is gastight and examined to verify that it has been installed in accordance with these Regulations; and
(b)after such testing and examination, any necessary protective coating is applied to the joints of that part.
(2) Where gas is being supplied to any premises in which any installation pipework is installed and a person carries out work in relation to the pipework, he shall also ensure that—
(a)immediately after complying with the provisions of sub-paragraphs (a) and (b) of paragraph (1) above, purging is carried out throughout all installation pipework through which gas can then flow so as to remove safely all air and gas other than the gas to be supplied;
(b)immediately after such purging, if the pipework is not to be put into immediate use, it is sealed off at every outlet with the appropriate fitting;
(c)if such purging has been carried out through a loosened connection, the connection is retested for gastightness after it has been retightened; and
(d)every seal fitted after such purging is tested for gastightness.
(3) Where gas is not being supplied to any premises in which any installation pipework is installed—
(a)no person shall permit gas to pass into the installation pipework unless he has caused such purging, testing and other work as is specified in sub-paragraphs (a) to (d) of paragraph (2) above to be carried out;
(b)a person who provides a gas supply to those premises shall, unless he complies with sub-paragraph (a) above, ensure that the supply is sealed off with an appropriate fitting.