Hi All, I have retired on a boat & fitted a Duetto Hot water system & initially switched it on in 12 volt & left it on as I have 720AH of LiFePo batteries & 1560 Watts of solar, so power is not a problem. What I would like to know. Has anyone else used their Duetto on 12 Volt only & have they had any problems. I have burned out 2 - 12 volt elements. The second in only 4 weeks. The 240 side works fine on the inverter when left on permanently it runs for 2 minutes every hour & a half to keep the water piping hot. I'm figuring I should only turn it on a half hour before I need it??? There are no water problems no leaks & it is set up below both inlet & outlet so it can't run dry. Has a dedicated DC contact breaker in the, tinned, 8mm square power wire with a trip current of 33.75Amps. The thermostat checks out Ok. Voltage is always between 12 & 13 volts. The hottest the Positive wire has been is 35.8C so below body temperature. This has me really stumped??? It has been suggested it is electrolosis or Galvanic action but no stray currents have been detected anywhere in the unit & there is no evidence of corrosion on the elements.
From the look of the fail point it appears to my uneducated eye that the nichrome element wire inside the tube has been too close to the tube when it was bent to shape. Some elements have pierced ceramic beads inside the tube with the nichrome wire running thru where the bead is pierced - the beads allow the tube to be bent and other types just us a chalky type of powder to bed the nichrome wire somewhere near the centre. Bending the tube can force the wire into close contact with the walls and then it will start sparking/earthing against the tube which is thinner at the bend....once a tiny hole is started the water gets in and Bobs your uncle.
I'd contact the manufacturer or agent.
