I purchased a Tempura 12-24 unit 3 years ago approximately and have been enjoying it until now!! Lately I have been experiencing intermittent hot water at the tap. I used to have the temperature set for 49 and it was more than enough heat to accommodate us but lately I had to increase the temp to full 52. Sometimes the little red light turn on indicating that it is heating the water and sometimes it does not. I find myself tapping the box with my hand and sometimes it works to get the light back on temporarily.

SOURCE: hot water tap only warm water in bathroom but hot in kitchen

Usually when you are having a problem at only one fixture, and not any others it is a sign that you have a faulty fixture. Hope this helps.

SOURCE: water heater not working after turning up heat

Did you turn the breaker completely off, then back on? When a breaker trips it is in a middle position, and nust be turned off to reset it, then it can be turned back on.

electronic & computer repair& servicre

• 12061 Answers
• Posted on Oct 31, 2010

SOURCE: The water heater does not

www.stiebel-eltron-usa.com/pdf/install_dhc.pdf
www.heaterstore.com/images_templ/dhc_heater-parts-list.pdf - United States
Above top, user and install manual, below is the spares list.
I think you may have a faulty thermostat sensor, or indeed the thermostat itself, i suggest you change that.. first just locate and change the thermistor, (sensor)... if that isn't it, then try replacing the thermostat unit itself.
Also check your regulator, on your supply, sometimes the diaphrams inside, get old, and stick a little sometimes

Please find below the master Google link, for Water heater troubleshooting.. use any of these great sites that will come up, to assist you.
http://www.google.co.nz/search?sourceid=chrome&ie=UTF-8&q=hot+water+heater+troubleshooting

SOURCE: The water heater "Stiebel Eltron

I am a free answerer, and I specialize in giving you resources for free
The paid answerers may have a person who knows your product and the problems associated with your model.
I believe they offer a refund if the 'fix' doesn't work.
The manual might also have troubleshooting.

Each day I see 20-25 unanswered questions about tankless water heaters.
And the day before, there were same number of unanswered questions about tankless products.
The number of questions shows the complexity of the machines, the brand-specific-ness of the problems, and the inability of the manufactures to take care of their customers.
If I understand correctly, the manufacturer will refer you to the installer.
There are not many ways a do-it-yourself-er can fix a tankless.

http://www.thetankatwaterheaterrescue.com/forums/forum3/

SOURCE: The unit is no longer heating the water. The red

This will be a thermostat or element problem. The red light tells us that you have power to the unit. If you are handy you can test the thermostat and the element with a continuity tester. A voltmeter may also be used. This will tell you where the fault lies.