Problems related to pier and beam foundations can be quite hard to pin-point as foundation problems since there are a lot of things happening with pier and beam foundations that would normally not be within a typical slab on grade foundation, such as the actual sagging from the beams involving the piers, or lateral movement in the piers, or uneven loading of the piers (the form of foundation failure).
So not only may a pier and beam foundation be subject a similar conditions that a regular concrete slab on grade foundation might be susceptible to, but a pier and beam foundation may have additional issues that could have next to nothing about the soil supporting the piers. Let's briefly talk about some of those non-soil related problems.
One from the main problems that you might have using a pier and beam foundation has regarding either deterioration (rotting) in the beams spanning between piers (if using wood beams) or excessive deflections (sagging in the beams). As wood beams grow older, they have a tendency to disintegrate because they're not well protected in the environment. As the years go by, the beams begin to increasingly sag, meaning precisely what those beams are supporting will also sag. A wall being based on these beams will start cracking, giving the illusion that you've a foundation problem. A structural Engineer would usually be able to let you know if this sounds like a problem
Another common problem for pier and beam foundations will be the lateral movement from the piers. In many instances a floor on the pier and beam foundation is several feet out of the ground, we've even seen houses around town with more than 4ft away in the ground. As you'll be able to imagine, when the wind pressure pushes against the house these wind forces must be somehow transferred back to the soil meaning the top of these piers behave as flag poles, swaying backwards and forwards with all the wind. It may stop noticeable towards the human eye, but the little movement will develop some cracks in the walls, supplying you with again the illusion that you have a foundation problem. Once again, an experienced Structural Engineer would be able to determine if this describes a problem.
Uneven pier loading is a second very common condition for pier and beam foundations. This is usually a problem with the design with the foundation as it pertains to knowing where you can put the piers. Heavily loaded areas (like load bearing walls) and lightly loaded areas (like within the middle of the living room) could settle differentially from one another if your design wasn't done efficiently from your beginning; which is, the piers on the heavy loaded may "sink" further than the piers in the lightly loaded areas if your piers were not properly engineered. This differential movement causes cracks in the floors (if using brittle finishes) and also cracks inside wall. This is a basis problem, but as well as challenging to verify it since it could be wrongly identified as soil movement due on the soil moisture changing. Your best bet is to buy a Structural Engineer to assess the situation.
We already went through a just a couple of samples of problems that you may face with a pier and beam foundation, so that as you can view, its not all problems have to do with the foundation. concrete engineers wa is a lot more than you would think. The moral of the story is, because the thing is that a crack it doesn't mean you have a foundation problem, and if you desire an honest and unbiased opinion then get yourself a Structural Engineer it doesn't help a foundation repair company.