We just replaced our gas hot water heater today. We bled the lines and are not getting any hot water to come out of our shower head. We have a stand alone single knob shower stall. The hot water comes out of the tub faucets just fine as well as the sink in the same bathroom. Our home was built in the early 1900's and has thick plaster walls (thus we don't want to have to knock out any walls to get the hot water running in the shower again.)

Our bathroom was just remodeled 2 years ago and the entire shower stall was brand new at that time. The bathroom is on the 2nd floor and the hot water heater is in the basement. Any ideas on what might be going on? If it's possibly just an air bubble trapped any ideas how to create enough suction to get it out? Thanks for any ideas and expert advice! Dawn

You didn't say but I'm assuming you had hot water to the shower before you replaced the heater. I'm also assuming you have cold water pressure at the present time in the shower.
What has most likely happened is that when the heater was replaced that the pipes were disturbed and mineral build up on the pipe walls flaked off and is blocking the hot water inlet ports of the cartridge. Turn off the water to the valve and remove the cartridge. Check the ports for any crud or trash that may have lodged in there. Now, before you reassemble the valve turn the hot water back on for a minute and flush out the supply lines. Did you get a full stream of hot water? Reassemble the valve and test it out. Let me know what you find. Regards, Tom

I agree with speedball, you have blockageCrud in the valve. If you don't want to disassemble/reassemble the valve you can BACK FLUSH the valve. Here is a procedure I use on my shower. If you have a pressure balanced shower valve this procedure may need to be modified. You can adapt this procedure to your own circumstances.

1) Turn off the water supply at the main house turnoff valve.

2) IMPORTANT: Locate any working faucet that will still deliver water. Try an outside irrigation faucet (I use one of the outside irrigation faucets. They still work since the line to my outside irrigation faucets split off before the main house turnoff valve). You can try the pressure relief valve after the pressure reducer on the main supply line. Perhaps you can use a neighbors water faucet.

3) Run a hose from the working faucet to the shower stall. Remove the shower head. Connect the hose to the shower head pipe. (You will need an adaptor to connect from a male hose thread to whatever pipe thread you have). (During the back flush you feed the water into the pipes here)

4) Locate a nearby hot water valve and a cold water valve. (The sink or bath tub). Remove any airators and open the valves fully so the water can drain out of the pipes. (This is where the water will exit during the back flush).

5) Open the single knob shower valve to full hot.

6) Slowly turn on the water in the hose and flush the line until you get a full clean stream of water.

7) Move the shower valve to full cold and flush that line also.

8) You're done. Put everything back the way it was and prepare to luxuriate in the shower.