tomo

I have the modular manifold plumbing system. hot water at tub is luke warm at best. all other faucets in the house have good hot water. No sign of a leak in walls around tub. also water is hot coming from water heater manifold source. Hot water was ok until recently. Seems like it must be blockage somewhere in the line. Could it be anything else?

Is this your first winter there? All newer shower/tub valves have a limit setting that controls how hot you can turn the knob. YOu may need to crank it up some now that the winter cold water is there, diluting the max hot volume you had that worked in the summer. That's one reason I prefer a themostatically controlled valve, they usually don't require changes season to season to maintain the max safe temp. It could also be a filter screen is partially clogged, or the pressure balance spool valve is partially stuck. Probably other things, too.