Water heater turns off in the middle of a shower

your not making sense with you question --state it goes cold in middle of shower --but state it will stay hot or cold forever ----if its the latter continued hot till you shut off water that normal working if the unit shuts down during shower then you have a problem ----unit is set at one temp and runs at that temp and you use shower 1 handle / 2 valve what ever you own to adjust temp their are really only 4 reasons stops making hot water ----2 are usually well water supply --incoming water pressure /flow or to cold ----other are gas valve -or sensor so i would look into your shower handles since almost all have adjustments and anti scold safety

Shower heads have flow limiters installed in them. This means the water heater cannot sense the water flowing and therefore it wont come on. Take the shower head off and look in the end for a piece of plastic that is in the swivel. Remove it. Then put the shower head back on.

Hello, Your Tankless water heater will briefly turn on when the propane is turned on and you switch it on but it only stays on when the shower handle is turned on to allow the flow of water. The water faucet must be on obviously. The unit will only stay on while the water is flowing out of the shower head.
If the unit doesn't turn on there is 3 things that will prevent it from operating correctly; 1. Batteries must have a charge /power. 2. The propane fuel must be on. 3. Water must be flowing from the shower head regardless of the spray pattern.
Good Luck!

I had the EXACT same problem (installed my tankless last winter and worked fine, now this summer it fluctuates, have to turn the shower completely off and then on again to get any hot water and then it only lasts for a couple of minutes!) Argh - it is frustrating!

Here's what I found: the demand for hot water is lower during the summer (hot) months because the "cold" water coming in is already quite warm. You don't need as much hot water to make the shower temp comfortable. SO, my tankless was shutting off due to low flow demand. I've removed the flow restrictor from my shower head and it helped alot but didn't completely solve the prob. Next step is what has been recommended to me by several people but is much more expensive - change the pressure valve on your shower to a temperature valve. Or just wait til winter and it should work ok again :)

Bosch tech support will ask you to turn off the valve to the water heater and open a hot water tap. If you have water flowing it is likely from a shower valve. My experience is Price Pfister shower valves are usually the culprit. Let me know how this turns out.

I am not sure if this is it but I had mine at too high of a temperature therefore I was not using enough volume of hot water to keep the heater on. They have a minimum amount of flowrate to sustain. Try turning the water temp down to 125-130. Hope this helps

Sounds like you have a problem with water flow. Since your ground water is warmer in the summer, you mix less hot and more cold in order to get the same warm temperature. If your hot water flow gets low enough, your tankless will start to "short cycle" in order to prevent scalding. Use one of these three methods to increase your water flow at the shower:

1) Clean your shower head and descale
2) Widen the hole in the showerhead's flow restrictor
3) Remove your flow restrictor entirely

Good luck!

Tankless water heaters normally take a little longer than a regular heater to provide hot water because they have to start and get warmed up. I'm guessing the heater uses a pilot light and that the short amount of hot water when you turn on the tap is hot because when the water is sitting still in the heater the heat from the pilot light is enough to get it hot. The tub faucet will get hot a lot faster than the shower because it lets a lot more water through and empties out the pipes faster than the shower. You could probably speed things up by letting the tub faucet run on completely hot for like 10-15 seconds and then turning on the shower.

Someone has not sized the system correctly. The water heater will heat a certain GPM a certain temperature rise. Most of those "generalizations" from the manufacturers are referencing the lowest of all the flow requirements like 2 lavatories. The truth is, don't use other fixtures while showering or get a bigger system. Lots of information related to sizing the tankless system at http://www.mechanicalengineeronline.com/Mini_Sites/Tankless_Water_Heaters_Ebook/Tankless_Water_Heaters.htm Have a good one. PS:Properly sized On-Demand water heaters are actually really good. Be prepared for the day your water heater quits.

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?