Shower knob

[polat2]

All of a sudden, after turning on the top knob, it turned on the shower for five seconds and then abruptly turned off. The bottom knob is temperature control. Any ideas not troubleshoot this? Is it simply threading gotten loose and needs to be redone? Thanks.View attachment IMG_6544.jpeg

 

[Geofd]

Does the chrome pipe with the shower head attach to a tub spout????? Can you show us the stem under the handle????

 

[polat2]

Does the chrome pipe with the shower head attach to a tub spout????? Can you show us the stem under the handle????

The knob just won’t come out. I think it’s all rusted - I think I have to drill a hole in the screw which most likely won’t work. Any other thoughts? Also attached all the connectivity to the back which I don’t have very good access to since it’s in the other bedroom but for my phone in there