many people are used to taking showers with very high volumes of water. That means taking high flow from both cold and hot sides. If the hot water as delivered to the shower valve is only at the desired shower temperature, that means taking a shower using only the hot water flow with zero cold flow.
Which for those people will feel like a very weak shower. The remedy for this is to increase the water heater’s output temperature so you can then dilute it with cold water at the point of delivery.
I suspect the OP wants his very high output temp to solve a volume problem.
Perhaps it’s as simple as lowering the water temperature to 120 or less. You may have it simply too high for the sensors to work (assuming one is perhaps not functioning as it should), perhaps even there is a safety feature coming into play.
Does the gas flow also get throttled to control water temperature, or is that just accomplished by mixing hot and cold?
The other thing stated above is perhaps your gas feed is not large enough.
If the math says you should get that flow, something seems off somewhere.
Well this makes perfect sense for tanked water heaters but a TANKLESS water heater which is what we are talking about will perform continuously.
It will deliver water 100% 200% -----1000% longer as it heats he water temperature on demand.
Theoretically, since my tankless water heater can run two hot showers simultaneously both of those showers can stay on indefinitely and remain quite comfortable.
Sorry for the long spell before posting.
I have not even asked my SIL how the heater is working for her. I have a couple other jobs to finish up this weekend and have planned to take my infrared temp gun along.
I added the 140 deg value because with the unit throttled to its lowest delivery flow I can get 140 deg F water according to the display.
I am also thinking about dish washing as of course my wife will pull the plug on the sink if she puts her hand in my comfort zone, but I cant put my hands in her dish water at all!! That is why I am interested in hotter water.
And I do have a problem that you good folks have pointed out and that is the Natural gas line is 1/2".
I did install a gas delivery flex line that claims its good for 80,000btu.
There is a summer winter selector that when in summer it cuts off one burner and I was thinking that would be a good setting if I was to add in series a second tankless unit.
I certainly don’t want to add a tank to this tankless system???
The biggest reason is she lives alone and her use just doesn’t need to have water kept hot any more than I do.
I will get back soon with the temp and flow readings and who knows she might be pleased???
Trouble with that is she would never complain because this is all gifted work and materials, but I do want thing to be good for her!
That may be the problem. If you have 60 feet of 1/2" line the gas carrying capacity is only 38 cubic feet per hour, according to this chart. Natural gas has around 1000 BTU/ft3, so already you’re at less than half the rated design, and that doesn’t include valves and fittings which introduce their own factors. You probably need a 3/4" line all the way.
I was responding to a side point raised by you when you said “I’m curious as to why anyone would want 140 degree water…”. I interpreted ‘anyone’ as “anyone who uses hot water”, not “anyone with a tankless heater”. Sorry if I missed your meaning there.
One point that the OP may have missed is that the hot and cold water are fed from the same source. If you run the hot water only and then turn a separate cold tap on, the flow of water through the heater will be reduced and the temperature will increase.
When the heater is installed it will be set for a maximum temperature. If the user is elderly for example, it might be set as low as 100F so that they will not scald themselves. It is, of course, adjustable by the user, and in normal use 115 should be about right as that will be too hot to put your hand in and allow you to dilute it with cold as you choose.
I did not make it to her place today but she is not very happy with the new water heater I was told by my wife.
Now Bob++, you stated the max temp may be set to some high setting. I have no idea of this being possible. The temp is basically controlled by 3 knobs on the front.
This unit is a Marey 10 liter unit. The 3 knobs are, 1 Gas control knob allowing the supplied gas to be reduced. watching flame through the viewing area and operating this control the flame can be viewed rising and reducing through the range of this control.
The middle knob is the summer-winter control operating this control allows 2 détente
positions where burners are closed off for summer settings. The 3rd Knob is the cold water supply control that allows throttling the inflow from full flow to a much reduced flow. Nothing is controllable for high water temp. My SIL had 166 deg F at low flow that was controlled by a sink faucet. Now the 30 deg F reading she had at full on is certainly puzzling but maybe the heating furnace was running???
Something I never thought about when I chose to do this job was life with a tankless system is much different than with a tank system.