Water Temperature Fluctuation

Anyone care to comment why water temperature would fluctuate at single handle faucets when in warm position. Water temperature would not fluctuate at the two handle faucets.

I have my theory, but would like confirmation.

2010 build house with Rinaii on demand gas water heater, city water supply with regulator valve.


I ran into this a couple of times and it was there was a cold line ran into the hot line somewhere or vice versa.

Mixing valve

My opinion is that the amount of water being used does not meet the minimum flow needed for the water heater to stay on. I think the early flow requirements were around 3gpm. Not enough for a single faucet using both hot / cold.

Another reason to really check out these units before purchasing.

On the efficiency side: The “Smoke and Mirrors” advertising about having “no storage tank losing heat all day” distracts many from the true efficiency----the Energy Factor… as measured by an independendent, long-serving org such as AHRI (Air conditioning, Heating and Refrigeration Institute).

Many EF’s for these units are in the low to mid .8’s while some other storage tanks can be in the low .9’s. In the end, a decision may depend on the actual different fuel costs in an area, not the EF’s.

My wife ( Char) does genealogy at the Church of Jesus Christ and they put in 5 of these units .
They had so many service calls in less then one year ,they had them all removed and went back to regular water Heaters .


This is correct.

Also, the tankless units will not allow you to adjust the temperature up hot enough to compensate for line losses.

If you want tankless, you better have it real close to the faucet or pay for a circulation loop and be prepared to pay for the luxury of instant hot water.

The size and layout of the house has a huge bearing on how these things work.

Ditto. :mrgreen:

Lots of easy work arounds, but a little thought needs to go into it.