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Gas fired water heater temperature control (C) Daniel FriedmanWater Heater Temperature Control FAQs
Q&A: How to Safely Set Hot Water Water Heater Temperature

Hot water temperature improvement and control questions & answers.

Tthis article series explains how to diagnose & improve the hot water water temperature that is too cool, and how to check water temperature safety in a building.

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Q&A on How to Correct Hot Water Temperature that is Too Low or Too High

Aquastat low limit controls hot water minimum temp (C) Daniel Friedman

These frequently-asked questions & answers about hot water temperature controls & settings were posted originally at this article WATER HEATER TEMPERATURE TOO COLD or TOO HOT - be sure to review the diagnosis and repair advice found there.

On 2018-01-31 by (mod) - is 100 F enough for dishwashers, hand washing, etc.

Perhaps for residential use 100 F is ok but as we replied to your question elsewhere, 100 degrees F is not sufficiently hot for commercial use such as in a restaurant. Commercial dishwashwers as well as residential ones generally include their own heating elements to produce the necessary washing temperature.

Keep in mind that for washing hands, it's not water temperature but washing time (20 seconds or more) and the use of soap that are critical. Certainly you'd not try to sterilize hands by using scalding temperatures.

Watch out: A proper, safe solution to "not enough hot water" can be obtained by increasing the water heater output temperature but also including an anti-scald device either at the point of use or at the water heater itself.

See ANTI_SCALD VALVES & HOT WATER QUANTITY

On 2018-01-30 by Phyllis

My apt hot water registers only 100*-- is this sanitary for dishwashers ,hand washing etc?

On 2018-01-04 14:26:50.127262 by joe

shower water goes cold

On 2017-11-04 by MOHAN NARASIMHAN

how to cater different degrees of heated water to different individuals lets say in a public toilet area

On 2017-06-04 by (mod) - make sensible use of hot water reservoir tanks

Ray,

In my opinion that's not a reasonable possibility.

One lesser question will be the standby heat losses in the remote old water heater tank that is just serving as a hot water reservoir.

I mean to say that if no one uses hot water from that tank for a time then it will cool off and people in that bath will not only not have hot water but it will take much longer for their water to get hot since you are going to require that the remote tank be completely reheated by the primary hot water source.

Second but more significant problem is the heating capacity of the new water heater. Your water heater is rated to heat water to a given temperature rise over at particular interval. The specifications are matched to the size of the water heater.

For example if your new water heater is a 50 gallon unit and you are now using it to try to heat the old plus new water tanks - say 100 gallons- to an acceptably hot temperature, you are doubling the work of the new heater and you're likely to be over tasking it.

I can see an option for making use of the old water heater tank provided it is in good condition than worth the trouble.

That is to use the old tank ahead of the existing new water heater as a temper tank, that is to act as a standing or holding tank to allow incoming cold water to rise to room temperature when no hot water is being run through the system. That reduces the temperature rise work that your new heater has to perform.

In that role the old tank would actually work better if it were not insulated as that would expose it and its water reservoir to the room temperature in which the tank is resting.

On 2017-06-04 03:33:45.089164 by Ray Hawkins

I am considering using an old water heater tank as a standby tank for hot water in the east end of the house, while using the newly purchased heat pump water heater to actually heat the water

If installed so that the new water heater supplies directly to one bathroom, could the hot water then be piped directly to the 2nd tank to increase the hot water available and decrease the wait time for hot water at the farthest away point from the new water heater?

It is approximately 80 feet from one end of the building to the other, with bathrooms on both ends.

On 2017-06-04 by (mod) re: how to make use of an old water heater tank, geyser, calorifer, cylinder

Ray,

In my opinion that's not a reasonable possibility.

One lesser question will be the standby heat losses in the remote old water heater tank that is just serving as a hot water reservoir. I mean to say that if no one uses hot water from that tank for a time then it will cool off and people in that bath will not only not have hot water but it will take much longer for their water to get hot since you are going to require that the remote tank be completely reheated by the primary hot water source.

Second but more significant problem is the heating capacity of the new water heater. Your water heater is rated to heat water to a given temperature rise over at particular interval. The specifications are matched to the size of the water heater.

For example if your new water heater is a 50 gallon unit and you are now using it to try to heat the old plus new water tanks - say 100 gallons- to an acceptably hot temperature, you are doubling the work of the new heater and you're likely to be over tasking it.

I can see an option for making use of the old water heater tank provided it is in good condition than worth the trouble. That is to use the old tank ahead of the existing new water heater as a temper tank, that is to act as a standing or holding tank to allow incoming cold water to rise to room temperature when no hot water is being run through the system. That reduces the temperature rise work that your new heater has to perform.

In that role the old tank would actually work better if it were not insulated as that would expose it and its water reservoir to the room temperature in which the tank is resting.

On 2017-06-04 by Ray Hawkins

I am considering using an old water heater tank as a standby tank for hot water in the east end of the house, while using the newly purchased heat pump water heater to actually heat the water.

If installed so that the new water heater supplies directly to one bathroom, could the hot water then be piped directly to the 2nd tank to increase the hot water available and decrease the wait time for hot water at the farthest away point from the new water heater? It is approximately 80 feet from one end of the building to the other, with bathrooms on both ends.

On 2017-03-17 by (mod) re: what to check if water temperature is only lukewarm

Start by checking water temperature at the water heater itself.

If the water heater temperature is too low I suspect

1. that you have an electric water heater

2. that its upper element is burned out

On 2017-03-15 by Ed Todd

I have no domestic hot water coming through faucets. it is lukewarm. I changed the mixing valve, but it is not getting hot.

On 2016-03-29 by (mod) re: water heater won't stop running

1. confirm that hot water is not running out of a tap or fixture somewhere that you've missed

2. if the burner still does not shut off but the water is not getting hot, then the burner is not operating properly, and could be unsafe (fatal carbon monoxide risk) - shut down the system

3. If the water heater temperature is not reaching the temp set by the heater's thermostat then there is a problem with the burner (or electric calorifer/heater/geyser elements)

4.Or there may be a defective water heater thermostatic control

Watch out: excessive temperatures or pressures at a water heater that won't shut off are very dangerous, risking both scalding burns and a BLEVE EXPLOSION (search InspectApedia for that phrase to see details)

On 2016-03-29 by Gale

Hi,
The water heater started working continuously, never stops. I had to unplug it. It is 100 gal. natural gas hydrojet heater.The water temperature after many hours, form old cold water to 18 hours, is just warm that I can put my hand under. My guesses are the burner, the thermostat (thinking that it is hot and keeps shutting and the other saying no let's warm it). Maybe it is the cold water pipe in the tank. ??? Thanks.

On 2015-12-22 by (mod) re: Shower isn't hot enough - look for the mixing or anti-scald valve

There may be a mixing valve at the boiler - an example is the photo at the very top of this page.

Depending on where you live, (e.g. Norway), mixing valves are also often installed at point of use in bathrooms and kitchens.

On 2015-12-21 20:44:25.633154 by Anonymous

Hi Dan, meant that i have the shower nozzle turned to the max hottest setting and it isnt that hot. someone mentioned a mixing valve? is that something that i can manually check myself? the aquastat?

On 2015-12-21 by (mod) hot water doesn't last

Sabreena I'm not sure what nozzle setting you mean;

But if nothing else has changed and your hot water is provided by a tankless coil at your heating boiler, it sounds as if the boiler temperature is not being maintained high enough. Ask your heating service tech to check the aquastat control settings and function.

On 2015-12-21 by sabreena

Hello, I have a riello boiler that is about 8 years old i dont have a water heater. Over the last two months the shower when turning on goes from hot hot hot water but only lasts a few min before it turns to just warm. what is causing this? even when i have it at the highest nozzle setting.

On 2015-05-12 02:29:07.356630 by (mod) re: new instantaneous gas water heater won't get hot enough

Wendy we offer some diagnostics for instant or tankless water heaters at

TANKLESS WATER HEATERS https://inspectapedia.com/plumbing/Tankless_Water_Heaters.htm

Start by checking the flow rate in gpm through the system and the temperature of the incoming water. These heaters can do a great job, but I've sometimes spent a lot of time fooling around to get the system to behave, especially when water pressure or flow rate or temperature is more than the heater is rated to handle. Remember that whatever the incoming temperature the heater can only raise that by a fixed maximum.

Try partly closing the incoming cold water to slow it down a bit through the heater to see what happens.

Remember that a tankless water heater is rated to raise the temperature of incoming water a specific number of degrees; if incoming water is very cold or if water is running too fast, either of those conditions could be the trouble.

keep me posted but better to post further comments on the Tankless Heater diagnostic pages.

On 2015-05-11 23:05:10.986010 by Wendy

Brand new gas instantaneous hot water unit is turned up to maximum but hot water produced is still only hand hot. How can this unit be turned up? The temperature of hot water is too cool even to wash wishes and too cool to have a shower. Builder inspected but says temperature set. What and how can I turn up the heat?

On 2015-03-27 21:12:24.480070 by Jill

Hot water runs through bath taps ok cold running through sink hot taps


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