E19 indicates the line voltage frequency is out of range. This could happen if the boiler is being powered from a small gasoline powered generator that is overloaded or not functioning correctly.
Inspect power wiring to the boiler and repair as necessary. If connected to line voltage, notify the power company. If connected to an alternate power source such as a generator or inverter, make sure the line voltage frequency supplied by the device is 47 - 62.5 Hz.
