There are national standards on the question, when do fire sprinklers need to be replaced? Sometimes it simply has to do with them reaching a certain age. According to NFPA 25 guidelines in sections 22.214.171.124.1, sprinklers installed prior to 1920 need to be replaced. Believe it or not, some buildings do have sprinklers that old!
Sprinklers that are heavily loaded with some type of contaminate such as dirt, dust or grease must be replaced. Additionally, sprinklers that require wiping or scrubbing, or using detergents or solvents to remove contaminants would also require replacement. Some building owners have painted their sprinkler heads to match the wall paint.
Any painted sprinklers need to be replaced. Painted sprinklers should never be cleaned and reinstalled, because the potential of damaging the assembly is too great. A “light” overspray or loading can be tolerated when a representative sample is tested to verify that the sprinklers will operate as intended. But an inspection professional needs to make this assessment.
Sprinklers that are leaking or that have been damaged must be replaced without testing. Dissolved minerals and other residues in the water can solidify as the sprinkler leaks. This hampers the operation of the sprinkler by changing internal clearances. It can also act like an adhesive, preventing parts from moving as intended. If corrosion is a significant problem, special corrosion-resistant sprinklers are available,
The best way to protect your sprinkler heads if you are planning on painting your facility is to simply cover the head and escutcheons with plastic wrap. Plastic hair bonnets or shower caps that have the elastic around the bottom also work well. Have your painting company use these to protect your sprinkler heads from paint. This will save you money in future replacement of sprinkler heads.