We have two showers one works perfect the other only cold water comes out when turned towards hot nothing happens..what is this

This is going to be a water heater issue. Not the head.

Be sure this hot water problem is just the shower.

Could be a chunk of scale in the valve. Need to turn off water supply and take valve apart. If nothing is found, turn water supply on to give line a 'quick' flush and turn back off. If this does not help, you probably have an obstruction somewhere in the hot supply line and a plumber may be needed unless you are handy. Good luck.

If I understand correctly, you have single handled shower faucet.
Normally there is a wait for hot water to arrive at faucet.
But now hot water is already at shower faucet.

Single handled faucets have a mixing area inside valve where hot and cold come together before going into sink.
This mixing valve can have crossover where the hot and cold can pass through to each other even when faucet handle is off. When single handle faucets get old, this can happen.
How it happens:
For example another faucet is turned on inside house, and pressure differential between hot and cold causes hot water at shower handle to pass through mixing area and into cold water line.
So if another faucet has been run, then that lets hot flow to faulty single handled shower faucet.
To confirm this is the problem: turn on other faucet and put ear against shower faucet to listen for moving water.
This condition may also signal there is a water leak.
The problem is not harmful, but will draw cold water into water heater each time, and is energy wasteful.
Replace faucet or have plumber repair problem.

Possibly switch off hot and cold water then undo cold water flange closest to the outlet and see if water comes out.if it does, tap assembly is faulty. If not, go back to where next available connection to the pipe was made. Work back untill you find the problem.

adjust ur anti scold the setting is set to low when single handle shower units are shipped they are set in cold mode for safety ur install/instructional paperwork explains such and also advises on how to adjust---remove handle and on shaft will see a blue and red plastic clips that are adjustable slide towards u and move red for more hot water test water continue till comfort level is reached for hot water

Hi,

This has happened to me in the past and had exactly the same symptoms but with a different valve. Before trying the below, it may make sense to be 100% sure that hot water is definitely getting to the valve .. can you get access to touch the hot feed pipe to make sure that it is in fact the valve at fault.

The following could be the issue:

1. The shower valve has a bit of dirt or gunk in it and is unable to allow the hot water through. It can happen with a very small amnount of dirt and is a real pain as it requires disassemble of the entire valve assembly.

2. The valve has failed and needs to be replaced - This was the solution to mine and was also significant in terms of effort.

Hope this helps, if so please leave feedback, if not let me know and I'll try and help some more!

you need to change the cartridge

I found a way to get warm water in the shower, but I'm not sure it qualifies as a solution. After trying everything else I thought that maybe when I was feathering the faucet in the shower toward the cold side so I would get warm water that at a certain point it blocked the flow on the hot water side enough so that the sensor in the hot water heater sensed there was no demand in the line and it shut the water heater off. To test this, I went to the kitchen and turned the kitchen sink faucet all the way to the hot side and then turned it on so that I got a small flow of water. I waited for the water to get hot to be sure the hot water heater was working. Once it was hot, I left it running to keep demand in the line and then I went to the shower and turned the faucet on. When the water got hot I started feathering the control towards the cold side and soon I had warm water. So I think I'm right in that the sensor in the hot water heater was shutting the water heater off when the demand in the shower was lowered to a certain point when I was trying to adjust the water temp in the shower.

So now I can get warm water, but it means I have to leave the hot water running at another fixture in the house to create a false demand in the system so the hot water heater doesn't shut down. Is there a way to adjust the senor in the hot water heater so that it will stay on when I'm using the shower only, so I don't have to waste water by running another faucet when I want to take a shower?