Water heater I have a 40 gal. electric water heater. Both elements are turned up all the way.  At first I was getting about 15 mins. of hot water.. Now I'm getting maybe 5 mins. of hot water.

Its your bottom element,if no hot water its the top if the top thermostat is not kicked out.you can do a voltage check at your bottom element,if 220 volts replace,but im very sure its the bottom if wires are ok..heres some tricks kill power and turn off the water to the heater.and open a hot faucet some where to let out the pressure, then close the faucet.then remove wires from your bottom element[it dosen't matter which way they go back] and use your element wrench with your new element ready,take out old and pop in new.you can use towels if in bad spot to catch little water that comes out.also sometimes the old element is hard to get out once loosed.[can depend on what kind is in there.but if its caught,just bend it what ever way it takes to get it out as fast as you can.with this method water dose come out but not very fast.the next thing is very important........once your new element is in before power is turned back on[here's the important part]you must fill back with water and open a faucet to let air out .when that's done you can turn the power on.other wise if top element not covered with water it will burn.if you need more advise i'll be glad to help.you can go to hardware store and get element wrench and element.the bottom element is the higher wattage .sometimes the old elements wont come out with out a fight.i use a torch and heat around the element on the tank to get that metal to expand.but you have to be careful with fire.any way i hope this helps you see what your up for.it may have taken me as a service call about 45 minutes. God bless ,tom

With amp meter check amps on element wire . If no amps check Voltage and terminals on element. Should be 240 volts. Only one elements heats at a time. Top element heats up first then lower element heats up. Amps should be about 18 amps if working properly. One other problem could be a leak in hot water pipe or dip tube may be off. Dip tube carries cold water to bottom of heater so incoming and heated water are not mixed at top of tank