We have been having trouble with the shower water temp. There are three valves (in the wall, which I can't get to). One is on/off (and pressure), the second is head selection (we have three heads: body jets, rainhead, hand-held), and temperature. It's the temperature that has been flakey. A small tweak counterclockwise and it gets cold. Opposite, it gets hot. There is no "warm".

Well, having just got back from a trip, we turned it on. On the hot side (if I tweak it), very little pressure (on full-blast). On the cold side, plenty of pressure. The hot lines seems to have cleared out the air (it sputtered a bit, and I ran both vanity sinks until they stopped sputtering). But still no hot pressure in the shower (sinks are fine).

Time to call a plumber? I'm assuming the valve is bad, but I don't know if there may be some air left in the shower line. It's not sputtering anymore. I doubt it could resist being pushed out by the water, so I'm thinking temp valve.

Thoughts?

(Note to self: turn off hot water heater before going on a trip...we left it on so daughter could use it, but she didn't much anyway)