Eemax280t2t no hot water

Could be a big build up of calcium and or lime in the bottom. No way to fix, you have to replace it..

Might be crossover caused by bad single-handle faucet cartridge:
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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If all the other faucets work, then the problem is the mixing valve in your shower. You will need a new shower fixture.

Water heater is heating water but only luke warm water arrives at faucet.
Open TP valve and confirm that hot water is available.
If water at TP valve is hot, then problem might be plumbing-related, for example crossover.
http://waterheatertimer.org/Crossover.html

Sounds like you have cold water entering the hot pipe, or crossover.

(A) Put bucket under water heater overflow pipe, and stand back from scalding water. Gently open and close the TP relief valve on water heater. Check temperature of water to see if heater genuinely has hot water.
It could be the water heater has sediment build-up and is no longer able to heat the water, or the gas thermostat is bad.
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
http://waterheatertimer.org/How-to-install-gas-water-heater.html

(B) If water heater has hot water, and hot is not getting to faucet, then you have a crossover problem somewhere.
1) This problem can be located at crossover point of a recirculation system, if re-circ check valve has failed.
http://waterheatertimer.org/Water-heater-recirculation-system.html

2) Failure of a single handle faucet cartridge can cause crossover.
Read how to test for crossover:
http://waterheatertimer.org/pdf/Crossover-on-single-handled-faucet.pdf

3) Other causes for crossover are a failed check valve elsewhere in the plumbing system, for example on the pool equipment. Also a failed mixing valve which is usually installed on top of the water heater so that some areas of the house like laundry room receive very hot water, while the kids bathroom receives lower temperature water.

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It sounds like your thermostat on the water heater isn't working properly. try turning it up higher and if this doesn't work I would have a service techy look at it.

There should be a temperature setting on the gas valve. It should be on top or front and have several settings normally vacation, warm and hot. Rotate dial towards hot setting to increase water temperature. Hope this helps. Thanks

Also check that by-pass valve(s) is/are, in proper position at back of tank.

Possible thermostat problem. Are you experienced enough in that area to do some testing. Have a multimeter? If not experienced, don't try it, too dangerous. Call in a service person.

if the leak is behind the handle take the handle off and tightn the packing nut, do not over tighten, as far as luke warm water is this with just one facucet on, they way these tankless water heaters work they are by gpm, gallons per min, if you have more gallons of water going thru the unit then it is designed for then it won't get hot, if your water pressure is to high going thru it will push it to fast thru the unit and won't get hot, your house pressure should be no higher then 75lbs no lower then 65lbs