Question about Bosch 2700ES Natural Gas AquaStar AquaStar 2700ES Tankless Water Heat

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Water temp. at the tap fluctuates

When I turn the hot water tap on the water is hot then in about a minute it turns cold, if i continue to run water in this hot water tap it will get hot again for about another minute then get cold again. The unit is installed in my attic with all the proper ventilation. I am wondering if it makes any difference that its hot in the attic now since summer is on us in Dallas.

Faye

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It is likely the inlet filter is plugged. this reduces the flow and then the heater adjusts the burn rate down to protect itself. the filter screens are small and plug easily. It would be a good idea to install a larger pre filter on these heaters.

Posted on May 30, 2010

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I have a new Bradford white 40 gallon gas hot water heater. There are no single handle faucets. The hot water fluctuates between hot and cold. When I close both inlet and outlet shut off for the hot water...


Sounds like water leak.
For example, broken pipe... or water running out of TP valve.
That would explain variable hot-and-cold water at tap.
Turn off all taps, and observe if water meter is registering water usage.

Jun 15, 2014 | Water Heaters

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Our rheem pronto tankless rutg-74xp red light will come home indicating hot water and stay on about 2 minutes and then turns off we have turned off and back on and let water run for 5 minutes and will come...


Before calling service technician, open following link for Rheem troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

List of causes MIGHT include one of following:
Bad household circuit breaker that powers electronics, or loose wire inside outlet where tankless plugs in.
Tankless fuses and control board.
Water flow rate too low. Minimum .8 gallon required (depending on model)
Tankless inlet filter clogged.
Household aerators clogged at faucets.
Crossover at single-handled faucet
If installed, there can be crossover at mixing valve.
Faulty household check valve, including check valve on re-circulation system if that system is installed.
Restriction in household water line, such as clog at elbow.
Unequal pressure in household hot and cold lines, caused by restriction in hot line. When single-handled faucet turns on, the cold water pressure is higher so hot does not flow and tankless will not turn on.
Loose wire connection inside tankless.
Unit temperature set too high.
Unit temperature set too low.
Water temperature is very hot coming out of tap, so more cold is added, but that reduces amount of hot water flow, so tankless turns off because flow rate is too low.
On some tankless, if water is preheated by solar or other indirect source, the burner will not activate.
High mineral content in water > delime tankless yearly
Misaligned temperature sensor
Low gas pressure. Wrong type of gas. Undersized gas line.
Too many faucets on at same time.
Faulty tankless water valve. Water valve stuck.
Fluctuating household water pressure, for example MUD and PUD district water pressure problems or water well pressure.
Faulty household pressure reducing/regulating valve if installed.
Faulty household pressure tank, if installed -or- pressure tank needs to be installed.

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I have a Powerstar Electric tankless water heater, 45-551301, installed in a new home less than 3 years ago. We have always had minor problems with the hot water staying hot, fluctuations in hot and tepid...


Tankless heater are a little frustrating sometimes but this is generally an issue of waterflow I believe. The fluctuations are do probably to the amount of water and rate of water going through the heater. If you have a shut off valve on the cold side of the heater, shut it back about half way. This will slow the water going through the heater and allow the heater to heat it up more efficiently. Then go to the shower, turn the hot on all the way (no cold) and allow it to heat up. Once it has heated up, test it by hand for a good temperature that you like. If it is too hot, turn the cold on just a bit until it comes to the temp you like. If it is too cold turn the hot down just a little (still no cold) and it will warm up. Ideally you should be able to turn the hot on full blast and then just turn on a little cold to get the right temp. Once you learn how these work then it makes it easier. You really cant run the water like you do with conventional hot water systems and expect to get the same results. Also, wanted to give you another little tip. Every 6 mos to a year, you should flush you heater with vinegar for about 30-45 minutes using a small cheap submerible pump like for a water feature in a garde. Just put in a bucket of vinegar and and run a hose to the "in" side of the heater and another from the "out' side of the heater and then back into the bucket. This will circulate the vinegar inside the heater and clean all the deposits that will DOA your heater. Funny how the manufacturer wont tell you this but these deposits will ruin the connectiosn on the heating elements. You can make your heater last for a long time if you do this.

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Hot water tank does not work when shower is on, it does however work when the faucet in bathroom is on. It quit working in the shower about a month ago.


  1. COLD MIX, HEATER DEACTIVATES
    If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04 Overcoming fluctuating temperatures [PDF].
  2. FLUCTUATING WATER PRESSURE
    If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
  3. CHANGING FLOW RATE
    Major changes in flow rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater's specifications. See: TWH E2-03 Outlet temperature vs. flow rate [PDF].
From the Bosch website.

Good Luck,
Gary

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Water turns cold very quickly


I had the EXACT same problem (installed my tankless last winter and worked fine, now this summer it fluctuates, have to turn the shower completely off and then on again to get any hot water and then it only lasts for a couple of minutes!) Argh - it is frustrating!

Here's what I found: the demand for hot water is lower during the summer (hot) months because the "cold" water coming in is already quite warm. You don't need as much hot water to make the shower temp comfortable. SO, my tankless was shutting off due to low flow demand. I've removed the flow restrictor from my shower head and it helped alot but didn't completely solve the prob. Next step is what has been recommended to me by several people but is much more expensive - change the pressure valve on your shower to a temperature valve. Or just wait til winter and it should work ok again :)

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Our water keeps fluctuating between hot and cold. The hot water will not stay on. It lasts about 1 minute and then turns to cold. After about 2-3 minutes it will get hot again?


The inlet line to the water heater goes to the bottom of the water heater to prevent the cold incoming water from mixing with the heated water at the top. The tube going to the bottom can come loose.

Turn the water off and relieve the pressure by opening a faucet and remove the fitting where the water enters the heater. You can see if the pipe is still connected.

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Fluctuating water temp. It is hot when I start the shower,


Iam guessing your using it faster than it makes hot water. May need a larger unit or a second one,in the system

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Fluctuating temperatures


Sounds like there is not enough flow in order to keep the burner in the heater firing continuously

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