Moyer diebel 500 ht tank heater will not heat up and indicator light is out. checked high limit, element, switch , thermostate , indicator light everything works when I put it in a different unit

The thermostat for the final rinse booster might be set too high causing the water to boil in booster tank. Water will then spray even when cycle is complete. Turn the thermostat down to 180f or 82c to comply with health regulation. If problem continues replace booster tank thermostat. Or if you have hard water pull thermostat and clean

There's only 2 wires doesn't matter which goes where. Check the hi-limit (small round disk) push the button with power off. You'll feel Click if it needed resetting

Hello there
The 500HT machine is very old one. Turn off the power first. To get to the elements you have to get the control box off first so you can get to take off the elements cover , now you can see the elements.
If the system have been wired wrong and short circuit it. the temperature control may have to be change too. I would change the two elements and the temperature control and the hi ltd control all together at the same time so you know that system have no problem anymore. All the best Dickson

A service man might have a used one kicking around. Or buy new.

Most electric hot water heaters have two thermostats, one near the top of the tank and one near the bottom, and are covered by removable metal cover plates. The thermostats are pressed firmly against the bare metal wall of the hot water heaters tank.

The top thermostat usually has a high limit switch that will trip if the water gets too hot. When it trips it shuts off the electricity to both the upper and lower heating elements.

To reset the high limit switch there is usually a red button that you must press. When the upper limit switch trips it is often an indication that something else has gone wrong with the heater.

When the top of the tank is hot the upper thermostat removes power from the upper heating element and transfers the power to the lower thermostat and heating element. If the lower thermostat is defective, then the lower portion of the tank will not be heated and the supply will be greatly reduced.
Check for power at the upper thermostat terminals where the power is sent to the lower thermostat and heating element. If there is no power then the upper thermostat should be replaced. If there is power then check for power at the lower heating element. If there is no power at the lower heating element then replace the lower thermostat.
If there is power to the lower heating element then it should be getting hot. If it is not, replace it. Another possibility is a broken dip tube. Check for a broken dip tube and replace if necessary.

Hope this helps out

Check the heater wiring with a voltmeter. Should be around 208v to 240v. If ok then turn off power and remove one heater wire and check heater with ohmeter for continuity. Replace if no continuity.

First item to check would be the high limit switch attached to the outside of the booster. Should have 2 wires. Switch is the size of a dime. The switch has a reset button at the centre. Just push in slowly. You should hear or feel the slight click. Do not touch the wire or terminal at the switch when power to machine is on.

The way you mentioned the unit have a 4 ft. cord at the back seem like a 50l LT the best way to determent is open up the bottom plate and see whether there is a booster tank in the right hand side.
Hope this can help you.

could be a number of problems. Checking with an ohm meter would determine the problem. Could be the booster high limit thermostat, a burnt wire, booster thermostat, or a heater element.

Without looking at your defective elements it sound like the chemical eat through the element and produce tiny pits tell your Eco Lab Tech to change to another type of chemical they have many kinds to suit your need. Try that . God Bless.