Just in case you haven't looked at all of the dash connection pipes , definitely check the water hose connections to the internal pipes under the center tunnel hard piping where it connects from into your water heater.
You should be able to check those easily without pulling the dash. If either of those let go you will have boiling water sprayed out over your feet, while having the windscreen obscured by steam. Unpleasant.
The under central tunnel heater hard pipes are a slightly larger diameter than the standard airbox inlet pipe spigots . In my instance a previous person had decided one size fits all and a smaller connecting pipe had been forced over the larger tunnel hard line and had split and was at the point of rupture when I found it.
Well worth a quick visual check if you have not already done it. I would be replacing every hose and clip.