We installed an eemax tankless hot water system & have no hot water pressure inside the house can you tell me why?

Contact their Support direct. It may be low water pressure.

https://www.eemax.com/products/eemax-flowco/spex3512

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Technical Support Tankless Water Heaters Eemax

There are two things to check. First, check the inlet water filter on the heater. The changing of the meter may have introduced debris in the line and partially clogged the filter, causing flow issues that affect turn-on/turn-off of the unit. Also, the new meter may have changed the water pressure/flow rate into the house, If the filter is not the problem, have the inlet water pressure/flow rate checked. If it is too low, there may be some adjustment that can be made, or the city may have to replace the meter with a different unit.

A lot of problems can contribute to this problem.
As you know, tankless cannot be exposed to water with more than 11 grains of hardness.
Tankless require softener and filter system which can affect line pressure and flow, which will adversely affect tankless unit.

The problem could be clogged sensor, bad board, but still that doesn't explain burned out elements unless the elements were coated with sediment.
Sediment build up will kill a tankless within 2 years and render it useless and unfixable.
Yearly deliming will not restore functionality.
If pressure is a contributing factor, you can add a pressure tank that will even out the pressure.
All in all it looks like the pressure sensors and other sensors are crashing.
Call service technician, and glean from that person the tips and tricks.

Read the manual for advisories and required yearly maintenance.

You can fix this tankless problem yourself, same day, by installing $207 tank-type electric water heater from box store. Offer 10% less and also buy flexible connectors to connect to existing water lines. The cost of running and maintaining electric tank-type is cheaper long term. All costs are energy.
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

Before calling service technician, open following link for Rheem troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

List of causes MIGHT include one of following:
Bad household circuit breaker that powers electronics, or loose wire inside outlet where tankless plugs in.
Tankless fuses and control board.
Water flow rate too low. Minimum .8 gallon required (depending on model)
Tankless inlet filter clogged.
Household aerators clogged at faucets.
Crossover at single-handled faucet
If installed, there can be crossover at mixing valve.
Faulty household check valve, including check valve on re-circulation system if that system is installed.
Restriction in household water line, such as clog at elbow.
Unequal pressure in household hot and cold lines, caused by restriction in hot line. When single-handled faucet turns on, the cold water pressure is higher so hot does not flow and tankless will not turn on.
Loose wire connection inside tankless.
Unit temperature set too high.
Unit temperature set too low.
Water temperature is very hot coming out of tap, so more cold is added, but that reduces amount of hot water flow, so tankless turns off because flow rate is too low.
On some tankless, if water is preheated by solar or other indirect source, the burner will not activate.
High mineral content in water > delime tankless yearly
Misaligned temperature sensor
Low gas pressure. Wrong type of gas. Undersized gas line.
Too many faucets on at same time.
Faulty tankless water valve. Water valve stuck.
Fluctuating household water pressure, for example MUD and PUD district water pressure problems or water well pressure.
Faulty household pressure reducing/regulating valve if installed.
Faulty household pressure tank, if installed -or- pressure tank needs to be installed.

Call the rep!

your water heater will take a 160 amps of you service. I would not install one if it was me. The total demand in the dead of winter with furnace, water heater and lights on will cause you to brown out.

Iam guessing your using it faster than it makes hot water. May need a larger unit or a second one,in the system

check circut breaker reset it then chek for power on both legs.

in and out hooked up right?