I have a Victron Multiplus 12/3000/120 on our boat connected to shore power (240V although probably closer to 220V) and three 110AH 12V leisure batteries. The typical background power draw during the day is 218W (fridge, freezer etc). It all used to work perfectly. Although we're hooked up to shore power 99.9% of the time so the inverter became a glorified battery charger. (the lights, water pump etc run directly from the 12V batteries.) However, we moved the boat and i tried to boil a kettle whilst not connected to shore power (1.7Kw should be well within the 3Kw) It got part way through the boil and then shut down. Since then, were back in a marina on shore power but with the switch in 'Charger only' position, i get mains on, float and inverter on LED's lit briefly before getting overload and low battery LED's lit constant before shuting down. With the switch in the 'On' position, i get mains on, float and inverter on LED's lit briefly before it shuts down. I disconnected and checked each of the three leisure batteries voltage (12.1V each), and the load at 240V (218W). The fixed wiring on the boat including battery connections hasn't changed. (battery leads are very heavy duty). I tried substituting another Multiplus 12/3000/120 and it showed the same symptoms.
any ideas would be gratefully received.