electric tankless water heater runs cold after 3 mins

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Old 07-19-19, 06:02 PM
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electric tankless water heater runs cold after 3 mins

hi, i have a brand new electric tankless water heater ('rheem 13' rated for one person household) just installed a few months ago. i didn't start using the unit until a couple of weeks ago.
when i turn on hot water at the bathroom sink, i get constant super hot water even after 20 mins so it appears that water heater is working just fine. the flow rate of hot water (cold water is off) faucet is about 1 gpm.

the hot pipe from the sink runs to the shower.

For the shower, i get super hot water only about 3 mins then the water temp drops to luke warm/cold. the total (hot and cold) flow rate of shower head is about 1.5gpm.

shower handle is a pressure balanced single handle. the handle rotates such that cold water comes out first, then hot.

the anti scalding limit is set to maximum to allow max temp.

when i adjust the valve so that hot water exits first when I turn the handle, as long as the handle doesn't allow too much cold water to be mixed in, i can get constant warm water BUT the water is not hot at all.

I have tried turning both sink and shower faucet on simultaneiously, but this made it worse. temp drops immediate on both fixtures.

I have read that it may be due to pressure balance of the valve but I am not sure if this online information is correct. I have moen 1222 posi-temp valve type.

Should I replace the pressure valve with thermostatic valve?
Should I just go with tank water heater?

Thank you in advance.
 
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Old 07-20-19, 03:46 AM
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I suspect it's a simple case of the water heater can't keep up with the higher flow. You can confirm by turning on both the shower hot water and sink hot water. If it gets cool sooner than usual and shortly after turning on the second outlet then the heater simply can't keep up. I would expect this to get worse in winter when the water entering the heater will be colder.
 
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Old 07-20-19, 05:10 PM
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thank you pilot dane. i'll probably end up replacing this unit with a tank version.
 
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Old 07-20-19, 07:51 PM
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what temp do you have it set for? 120f? 110f?

Try turning it down if you have it up high..

What part of the country are you in?

If the shower head is indead 1.5 gpm you should get anout a 60 f temp rise... meaning if incoming water is 60 f then the heater will raise it 60 f more to 120f...

also on new installs there is a screen on the inlet of the tankless that often gets clogged.. Check inlet screen.

That unit should work fine..

Have both heating elements checked and insure there is power to both. ie: both breakers on.
 
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Old 08-09-19, 04:03 PM
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mcharon, hello have a Bosch AE125 with 3 kids and a wife since 2007.

We have a well, the first day we installed it my daughter was playing with the hose and I had one hell of a shower (heater shut off due to flow and had to recalibrate not fun).

That said now it's just wife and I, on demand can save money.

We have to run the water up to temp before we use the dishwasher, inconvenient.

Taking a shower must anticipate ups and downs of well pressure.

But hey 12 years + out of a hot water heater !

Good luck
JOB
 
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Old 08-10-19, 04:09 AM
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If you are noticing the ups and downs in water pressure when showering I suggest checking the air pressure in your pressure tank. With your water system turned off and all water pressure bled off the air in the pressure tank should be 2-3 psi less than the pressure at which your pump turns on. When set properly it's really hard to tell when the well pump is cycling on and off.
 
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Old 08-10-19, 12:10 PM
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Thank You Pilot Dane will check out air in pressure tank.
 
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