Grohe bath faucet adjustments

The inlet must be turn on as well as the outlet side (a hot water fixture) so that water can flow through the system. Make sure that the plumbing connections are correct.

It *may* not be a problem with the water heater itself necessarily. When you say "keep adjusting the water temperature when you're taking a shower" I presume you're talking about turning the shower hot/cold knob(s) and not the temp thermostat on the water heater itself.
If so, when it starts to run colder, turn the knob all the way to full hot. Is the water then very hot? If so, the water heater is working fine & doing its job, and the problem is likely to be in the shower faucet mixing valve itself. Sometimes a faulty one will expand the inner seals/cartridge as hot water flows thru it, and starts to (wrongly) restrict the hot water flow, thus causing the constant need to "turn the dial up a notch".

Increase your flow, sounds like you are right at your activation rate.
1 way is to turn down the temp on the machine, so you dont have to mix in so much cold at your shower. Check to see if your mixing valve is bad, or your showerhead has restriction/scale built up in it.The other way is to turn on your lavatory fixture full hot before showering(which will keep hot water flowing through the machine as you adjust your temp to be comfortable.

Before you install the temperature control knob, adjust the valve body (47111) with a wrench to set the temperature to "100 degree or close to it". Now, place the limit ring to tdc (top dead center) and control knob with the red 100-degree align to it. Your problem may have been the valve's temperature setting is out range when you installing the temperature control knob.

The thermostatic stop is set too low. Havent set a grohe before but most other thermostatic shower valves work similar. pull off the handle(however a grohe handle comes off . . ) there should be a notched ring or stop which keeps the handle from going all the way hot. pull out the ring and turn it a few teeth hotter put back and reinstall handle try water temp and adjust again if necessary.

Do you mean the other faucets in the house are hot and only the shower is warm? If so there is an anti-scald adjustment on the faucet that needs to be turned up a few notches. Havent adjusted a Grohe faucet but most faucets you rmove the handle and behind the handle is a nothced adjustment ring that prevents the faucet from getting too hot. This ring, or stop, is pulled out and twisted clockwise(or counter clockwise to set higher or lower max temp, then pushed back. maybe you can look up grohe to see which way ring or stop adjusts for hotter water.

It could be back flowing into the hot water heater tank which is not full because of the leak. Even though the valve is closed on the cold water entry side, there is probably no valve on the exit side. That is how it is returning to the tank.

they have it installed wrong it is pulling from the wrong side, it is supposed to pull ot water up to the fixture but then if it stays hot on the cold side they are backwards

chk for shut off valve to heater , open if closed. Open hot water faucet and listen for water pump. if pumping givre it time to fill heater tank and start runnuing out offaucet. Air will be purged as pump fills the lines and heater. Shoer and bath need hot faucets open also to purgr air.

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?