David we have the same model, and when it was installed had a problem with it, as the unit is about 2 yrs ago I can't quite remember what it was but had a problem of booting up and giving the low pressure warning and the water was only luke warm, the triton guy knew exactly what it was straight away and replaced the circuit board in the control panel (on/off panel part - he said it was good job it was on the control panel as apparently the heater box was inaccessible at least for him where the plumber had put it - anyway another story) - all this is slightly irrelevant really I guess, but one thing that I did note was the flow rates - apparently our water pressure is only just enough and we found that when we had the filter bit between the water intel pipe and the unit sometimes the low flow rate light came on, and wouldn't work - so we took out the filter bit (I know you shouldn't - but it worked for us!), but from memory with the filter in and on full cold on we were getting something like 15 litres / min (I can check this a weekend with filter off - if you wanted), so its just occurred to me that although your pressure is okay I wonder if your flow rate is okay - the manual says it needs a min of 9 lit / min!!
Jon