leaky wh from overflow tube

i have a bunch of rentals and in two of them the overflow tube leaks on the water heaters. Is this as simple as installing a pressure reducing valve?? do i ALSO need to install a expansion tank?? why does this happen.. thanks in advance!

Rig up a pressure gauge and check the house pressure.

If it's under 80lbs. just change the relief valve that is leaking now.

The problem could just be a defect TP valve. Simple and cheap to replace. So first check the pressure of your water supply with a gauge. If it is much over 60 psi, you should have a pressure regulator valve on the supply. If you do need a PRV, then you will need an expasion tank too. The PRV creates a closed system which prevents the heated water from expanding back into the water supply and results in a huge rise in tank pressure and trips the TP valve. If the pressure gauge shows normal pressure, then just replace the TP valve.