Hot water in sink luke warm water in shower

[dmmsr]

The water heater is maxed out. Look at the math above.

But if he wants to check for a cross connection just turn the cold water off to the water heater and go to the lavatory faucet and make sure once the initial hot water pressure is relieved that the flow stops on the hot water side.

I am not saying that I'm right on this one. I am just throwing out a possibility. The problem I see is that of why does it get hot when he runs the sink? It would stay tempered if the flow rate is the issue. Maybe a slight increase but if it cannot keep up with the demand it should stay a low temp. But when he uses the cold water and slow the cold water down and pull it away, he gets hot water. My thought, and only my thought is if you put a lesser gpm shower head it is only going to decrease pressure coming out at the same point not temp due to the temperature balancing. But once you pull cold water away from going to the diverted the temperature increases. Why only then? When he had a tank he had the reverse he got hot water until somebody turned on a faucet elsewhere and it got cold. Maybe one temperature balancing diverted is bad but he stated he replaced it. But two are bad? There has to be something with the piping if you pull water from it and it changes the temp dramatically. Again this is my feeble mind at work without being on site.

 

[Twowaxhack]

I am not saying that I'm right on this one. I am just throwing out a possibility. The problem I see is that of why does it get hot when he runs the sink? It would stay tempered if the flow rate is the issue. Maybe a slight increase but if it cannot keep up with the demand it should stay a low temp. But when he uses the cold water and slow the cold water down and pull it away, he gets hot water. My thought, and only my thought is if you put a lesser gpm shower head it is only going to decrease pressure coming out at the same point not temp due to the temperature balancing. But once you pull cold water away from going to the diverted the temperature increases. Why only then? When he had a tank he had the reverse he got hot water until somebody turned on a faucet elsewhere and it got cold. Maybe one temperature balancing diverted is bad but he stated he replaced it. But two are bad? There has to be something with the piping if you pull water from it and it changes the temp dramatically. Again this is my feeble mind at work without being on site.

It gets hot when he runs the lavatory because he’s not flowing much hot water.

Again, the math proves the water heater is working properly based off the rate of rise the heater can produce.

His incoming water is too cold for that water heater to take the standard shower of 2.5gpm.

Look at the specs of the 13kw in the chart I posted.


Look at the temp rise at various flow rates, 1.0gpm(89 degrees) 1.5gpm (59 degrees) 2.0 gpm (44 degrees) now look at his incoming water temp…..add the two together for the selected temp rise at the selected flow rate.

 

[Rickyman]

Don’t worry, you’ll get a hot shower in the summertime

 

[dmmsr]

It gets hot when he runs the lavatory because he’s not flowing much hot water.

Again, the math proves the water heater is working properly based off the rate of rise the heater can produce.

His incoming water is too cold for that water heater to take the standard shower of 2.5gpm.

Look at the specs of the 13kw in the chart I posted.


Look at the temp rise at various flow rates, 1.0gpm(89 degrees) 1.5gpm (59 degrees) 2.0 gpm (44 degrees) now look at his incoming water temp…..add the two together for the selected temp rise at the selected flow rate. View attachment 37909

Got it. I was not trying to against what you said. Sorry for that.

Now all he has to do is pipe his tank water heater to his the cold inlet of his tankless and he should be good. Lol

 

[Justinwayne]

The water heater is operating correctly.

The max temp rise is 59 degrees ( at the water heater outlet) flowing 1.5gpm.

47 degrees incoming water temp
+
59 degree temp rise
=
106 degree shower at 1.5gpm.

So it’s leaving the water heater at around 106 degrees. By the time it hits your skin…….

You get the idea.

Water heater is too small at your incoming water temps to flow a normal shower volume.

Yea I thought i calculate it properly. well I guess I will just keep the flow reduced to get my desired results. I ordered a low-pressure shower nozzle. I guess this is my work around for now..

 

[Justinwayne]

Cross connection meaning that he could've somehow piped the cold to the hot directly. I had went to a job where the landlord replace the water heater himself and right after had the same issue. I found a pipe that did not look right and found it was the cold water line piped to the hot. Only the shower was affected. They had to run the cold water in the kitchen in order to take a hot shower. I wouldn't think it could be possible but have seen it myself. I thought he piped the water heater wrong. Checked the dip tube. Shut off all fixtures. It took me several hours to find it.

I did not.... if i did everything would be reversed... hot would cold and cold would be hot......

 

[Justinwayne]

I did not.... if i did everything would be reversed... hot would cold and cold would be hot......

thank you for all of your replies. The answer is what I figured, wrong size tankless heater. I did a work around now I have hot water in the shower. Thank you, you all were a big help.

 

[dmmsr]

I did not.... if i did everything would be reversed... hot would cold and cold would be

What I meant is if you tied both the hot and cold together. I did not mean crossed the lines. I had a job that sounded just like how you described the situation.

Anyway did not mean anything bad by it. Just a thought.

I'm glad you got it worked out!