When showering the water will very quickly go normal temperatures to either scalding hot or freezing cold. It will do this every minute or so. Is this to do with my showerhead or the inner plumbing of my building??

My first question is how does the water work in any sinks you have? It the temperature varies in them, then it likely it is the incoming water. Do you have your own water heater?

If the sinks are fine, then I would look at the shower controls. How free are you to work on the plumbing? I have never lived in a co-op. I have either been a tenant, or since 1973, a homeowner. If you can, shut the water off to it and take the shower controls apart. Clean up or replace everything you can get apart. How old is the plumbing? The older it is, the harder to get apart and to find parts.

Newer stuff, you pry a cap of the knob, remove a screw, pull the knob off, and then the insides screw out. Once you have the insides out, maybe take them to a good hardware store, ACE, Top Value, etc. Let the help match up your old parts.

Post back if you need more help.

I usually leave unanswered question go hoping Tom or another good member will answer. I got an email about this one.

You might ask your neighbors if they have a similar problem, if it's a building problem you won't be the only one to be shocked out of your skin in the shower. Your shower head won't cause this cold/hot reversal but a mixing valve could if it is not secured into the valve body. Start by asking the neighbors the take it apart if you're the only one. Answer Labmans first question and that may tell us a lot.