Navien NCB-240e combi: domestic hot still flaky after replacing flow sensor…

[Tripp Knightly]

So I took my shot. A failed flow sensor often causes unreliable domestic hot. Seemed fixed for a few days after I replaced (cheap on both part and my DIY time).

Before going to the 3-way valve (above my pay grade!) would 5+ years of no de-scaling cause this? I have to de-scale and especially sooner if plausible.

 

[Fitter30]

Find mineral depots in the old flow sensor? Mineral depots are death to a heat exchanger. Mineral depots are a insulator causes hot spots, warping of the whole heat exchanger and if it would be under warranty they wouldn't cover it.