Booster Pump starting to Wear Out ?

I have had a Mitsubishi WP-305Q3 pressure booster pump installed at my two-story home for four years now. It has gradually, over several months, begun to behave strangely. If one takes too long to shower on the second floor the pump stops working and the water stops flowing. Then one must turn off the shower tap and wait for a few minutes. After that, one can turn the shower tap back on again, and it works normally -- until the next time. My uneducated conclusion is that the pump is over-heating and is trying to protect itself. My question: Is this a reasonable conclusion, and if so are there repairs that can be made, or is the pump just wearing out and will have to be replaced? Thank you very much for your thoughts.