Although the creation of PEX materials did eliminate many of the problems that are associated with metal piping materials, there are still a few problems that commonly affect PEX plumbing systems. These problems are relatively mild in comparison to the cracking, breaking and soldering that metal piping material has become known for. PEX is known for being much easier to install than other types of systems because it is flexible and less connections are required in the average plumbing system.
One major problem that is associated with the use of PEX pipe is that it is not able to be used outdoors. PEX is only meant to be used underground and indoors as a water delivery system. PEX is resistant to freezing temperature and will expand as ice forms in the pipe and will contract as the ice int he pipe melts. However, the pipe will not resist a hard freeze when it is placed out doors. This is one of the reasons why California requires that even pipes that are placed underground have a sleeve throughout the entire distance that it is underground. Most states only require that a sleeve is placed where the pipe enters the building.
Another common problem that is associated with PEX plumbing is damage from rodents. It is a common problem, particularly with piping that has been placed underground outdoors. Rodents will attempt to chew through the pipe. Sometimes they are able to completely break through the pipe with their teeth, and other times they are only able to cause a leak. Either way, this spells bad news for inexperienced plumbers and can be quite hard to find and deal with.
Another common problem that is often associated with PEX piping material is the presence of biofilm, caused by bacteria int he pipes. This can cause a number of different issues within the system and is most commonly found in non-chlorinated systems or in systems that do not see much use throughout the year. Often times this problem is seen in cabins and vacation homes. Systems that fall into these categories should be sterilized every so often to ensure that this does not occur.