I have three bathrooms in my house and in two of them the hot water in the tubs don't work, but the sinks do have hot water.

Hot water cartridges/stems must be clogged. You will need to shut water supply to bathrooms or even to the house, remove cartridges/stems, pulse the water (rag over the valve) and then re-install the cartridges/stems.

Worst case, you may need to replace the stems.

Let me know what you think here...

MARK