There is power to the system but when you turn water on elements do not come one and heat water. all phases have 238 volts to them. why will system not turn on and heat water

Do you have 3-phase water heater? Is this balanced or unbalanced 3-phase unit. Add comment and describe product in detail, including brand since i have some service resources for both types.
Or do you have ordinary residential split-phase 240Volt Bosch tankless computer that heats water, and has 2 or 3 separate elements, and a separate circuit breaker supplying power to each element? And testing across both hot leads coming from each breaker yields 238Volt?
Copy following link for Bosch tankless manuals, with brief troubleshoot section that does not provide detailed service procedures for repairing tankless computer:
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html#manual
If this is new water heater, then call installer. If you installed yourself, then remove tankless and return to seller for refund.
Tankless computers require certain amount of water flow to activate computer sensors. Turn on Hot tap and listen to pipe to hear if water if flowing through hot pipe. Check for crossover:
http://waterheatertimer.org/Crossover.html
Clean water filter usually located just above where cold water connects to unit.
Delime tankless ... and use water softener. Tankless cannot be exposed to more than 11 grains hardness in water, or parts will fail within 2-3 years. Simply deliming tankless heat exchanger each year will not maintain full efficiency... although for typical family of 4, tankless comper water heater costs $100 more to operate than tank-type heater according to manufacturer's promo literature and independent studies.
Call local technician who specializes in fixing tankless computers. For plumbing problems call local plumber. These are two different things.
If tankless computer is older, then cut losses, and buy tank-type electric water heater at Lowes for $285 and make quick changeover and have hot water same day. Sell old tankless on ebay and cheat next guy, or sell at scrapyard for $3 per 100.
Gene
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