Warranties NEVER cover ALL parts. Especially those that can be damaged by neglect or bad chemistry.
For example, they say things like "10 year plumbing warranty", but don't mention that they don't consider jet inserts to be "plumbing". So when your spinners start blowing ball bearings into your spa, it's not covered. Same goes for gaskets/o-rings, light bulbs, and even heaters and pump seals in some cases.
Likewise, there are exclusions, such as freeze damage, which is considered neglect even when it resulted from the failure of a warrantied part and you called for service the day it tripped the breaker but the dealer can't get there til next tuesday and by then it froze. Not covered.
You can read the fine print but it won't help. You only find this stuff out after you submit a claim and it is denied.