Help, we can only get hot water out of one faucet/ shower head at a time.

DezirayClick

I have a munchkin boiler system in which I know nothing about. It is approximately 14 years old.  When we have hot water going in one shower no other shower can get hot water nor any other faucets. We also can rarely get truly cold water, at the best it might be room temperature at its coldest. Our master shower runs very hot. It has not always been like this.  The first 3 to 5 years we lived in the home we were able to run multiple faucets/showers  at a time.  I’m wondering if it can be a problem with a stuck diverter valve or something? We are located in OKC so if you know of anyone that is an expert in troubleshooting boilers please let me know. 

Zman

I don't think it has anything to do with your Munchkin or hot water tank.
You likely have a cross-connect between the hot and cold water pipes somewhere in the house. What has changed? Did you recently add a component? My guess is one of those shower head wands that lets you turn it off at the head is left in the off position with the main shower valve turned on.