We have a gas water heater that operates on demand relative to flow. The far bath gets hot, but when cold is added the hot quits. We have a well and pressure tank. For a while we could run hot water in the sink and keep the shower flowing hot, but now that doesn't work. We have a larger pressure tank we could switch out. The tub and sink work okay, but if too much cold is in the mix, the hot stops. We have the water heater set to operate on the lowest possible demand. Our water is high in lime and fixtures clog quickly, but alternating a freshly vinegar soaked shower head does not help much.

Is the unit shutting off on low flow, or is it scaled up so badly it doesnt put out what it should? Has it ever been de-scaled?

We descaled recently. Output is high to tub.I just removed the flow restrictors on the shower head and that helped a lot.



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you need to have someone hold the hot water pipe at the water heater and have someone else duplicate your problem. see if the hot leaving the heater stays hot or cools down.

What. Rand and model of tankless water heater is it ? Some brands have a dip switch that needs to be set for well use.

If the heater operates on a flow demand basis, then an easy solution to the problem is to reduce the cold water flow and bring the hot flow back up. If the temperature can be adjusted on the heater, reduce the output temp and a shower at the same temperature will require a higher hot water flow. From the need to keep the sink on at the same time to get hot water, I think this will take care of the problem. Also, if you can insulate any open piping it will help as well

Well, we bought it online from Puerto Rico and the manual leaves much to be desired. Isn't a dip switch for checking oil?

Took a shower and it stayed hot, but had to leave some hot flowing in the sink, too.

Oh, we can see it turn off. I figure it has to be a low flow demand.

Yes, I could lower the temp, but I like a hot shower, and I'm kinda lame and have to work my way up to that highest temp. And I like really hot water for washing clothes and dishes. No insulation needed. This is central Texas. Yee haw!

"No insulation needed. This is central Texas. Yee haw!" Good to know that the laws of physics don't apply to you. We can now be sure that your problem is assuredly gremlins.

Let us say that you like to take a shower at about 110 degrees F. If your water heater is set to 140 degrees and your incoming water temperature is say 70 degrees, then we can say that to achieve that particular mix from a 2.5 gallon per minute shower head you will need 1.07 gallons per minute of cold water, and 1.43 gallons per minute of hot water.
Now, if you were to adjust the water heater settings to 130 degrees, you will need 1.67 gallons per minute of hot water. If the heater was set to 120, then you would need 2.0 gallons per minute. Now for purposes of discussion since we don't know what any of your temperatures really are, let us say that your water heater requires 1.5 gallons per minute of flow to activate. This would explain why letting a sink run in another location allows you to get a hot shower, but only cold when the additional hot demand isn't present. If the problem is insufficient demand (as it appears) to activate the heater, reducing the temperature settings will solve the problem.

I would illegally remove the flow restrictor from my shower head, to allow more flow.

Oh, I already did that! Our grey water goes out in the yard and sinks back into the Edwards aquifer.

Thank you so much! Reducing the temp has solved the problem.



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