In some marine applications where you are using your 12v or 24v heater, which is powered through an inverter, this will be causing the glow plug to blow see our article below which will answer your questions.
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Their opinion was that it was blown by a voltage spike, I was plugged into the mains shoreline via my Victron combi at the time and the man from Mikuni thought this was the source of the spike and I should check my settings on the Victron. However the Victron's performed faultlessly for 2 1/2 years and nothing else has succumbed to voltage spikes (even cheap EBay LED lights), and I'm pretty certain I set it up correctly when I fitted it. I did however notice it had switched from Float to Absorption mode last night (I think it does this automatically periodically to condition the batteries), and it is possible that it did that switch while the Mikuni was igniting (so the plug was powered up).
What do people think, does voltage spike seem plausible, if so is there anything I can do to stop it happening or to protect the Mikuni. Are there any particular settings I should check on the Victron?
P.S. I also have a Smartgauge fitted, and over the summer when I had left the boat a few months it was showing a "high voltage" error code when I returned, would this be caused by a spike? It didn't show any such error code last night though.
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Mikuni are correct and you wont see the voltage spikes as they are to quick!
Took me ages to get to the bottom of this with my battery charger.
In the end I binned it and bought another one!
Or you could fit a timer so its off when the mikuni is on.