I just bought a 10 yr. old Schult mobile home and after moving it to a new lot, I have no hot water. The heater is an Intertherm. I checked incoming voltage and it is ~120v, and the plate says 240v. My father in law says it doesn't have 240 wires to it, but I don't know (three wire). I tried the red reset button as suggested by Heatman101 but didn't push really hard (will try again). If 120v is the correct voltage how do I check the elements? Thanks in advance, Matt in trouble with wife

Sorry we do not have that kind of information available here.

How to Repair or Replace Defective Water Heater Dip Tubes

www.familyhandyman.com > Skills > Plumbing
The role of the dip tube is to direct incoming cold replacement water to the bottom of the tank for heating. While it warms, the dense, cold water stays naturally segregated from the warmer, lighter water floating on top. The water for faucets and appliances comes from the hot layer on top.

There is a suprising lack of information on those water heaters. Do you have any idea how old it is? Is it in a mobile home?

remove the two covers one high and one low and set the temp higher. This time of year with colder water comming in the house the water heater has to work harder to raise the temp of the incomming water. In the summer the incommong water is much warmer. 40 gal is a small water heater and you will only get about 15 gal of hot water with the ice cold water entering the water heater as you use the hot water. You can get a bigger water heater. even better is to go tankless and a have never ending hot water and save money at the same time.

Check plumbing.
Bad single-handle faucet cartridge can can hot never to arrive at tap.
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Install 30 amp breaker and run 10 gauge wire from breaker box and install electric water heater for $300 total.
http://waterheatertimer.org/How-to-replace-circuit-breaker.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Check that you are receiving 240Volt across top 2 screws on upper thermostat.
Copy following link for troubleshoot resources:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have clog in the water line.
Since all hot water pipes are involved, clog is probably near water heater.

Buy pressure gauge at hardware store that threads onto hose connection.
Brady BTG 100 at Amazon
Picture of gauge

Check outdoor pressure for baseline pressure in your home.
Turn off electricity to hot water heater for an hour or two so there is not scalding water.
Open drain valve on water heater to see if water heater is clogged with sediment.
http://waterheatertimer.org/Water-heater-will-not-drain.html

Put pressure gauge on drain valve and compare with outside pressure.
Open hot water spigot on bathtub and see if tank pressure drops ... if tank pressure drops significantly with bathtub spigot on, then clog is on incoming cold water before tank, and could be on outgoing hot water pipes too.
If tank pressure stays about the same, then clog is on outgoing hot water pipes.

Clog can be sediment caught in cold water shut off valve located above tank. Open and close valve and test pressure again. Take apart incoming cold water pipes above tank and check for sediment. Replace valve. Look at condition of cold water nipple on top of tank.

Sediment caught at hot water elbow near tank.
Sediment can fill up old pipes. Take apart hot water pipes above water heater and see condition.
Look at condition of hot water nipple on top of tank.
You may have to take apart pipes up to first or second elbow.

Pipes can decay at joint where copper pipe connects to galvanized pipe. Check for copper to galvanized connections on cold or hot pipes and replace section of galvanized pipe. Copper pipe will probably be good, the galvanized pipe will deteriorate. Replace copper-to-galvanized joint with 3/4" non-conducting union from hardware store

The slightly warm water makes me think of a thermostat problem. The fact that the heater is 10 years old I wonder how hard your water is. Calcium build up kills water heaters. But the yellow flame you mention could be the results of dirty orfices. May want to have a Pro look at that.

Tankless water heaters normally take a little longer than a regular heater to provide hot water because they have to start and get warmed up. I'm guessing the heater uses a pilot light and that the short amount of hot water when you turn on the tap is hot because when the water is sitting still in the heater the heat from the pilot light is enough to get it hot. The tub faucet will get hot a lot faster than the shower because it lets a lot more water through and empties out the pipes faster than the shower. You could probably speed things up by letting the tub faucet run on completely hot for like 10-15 seconds and then turning on the shower.