Water is still off.

Checked dewpoint sensor still flashing red light (indicating an error). Pipes warmed. Not what I expected. Possible fault?

I checked S4's ambient temp/humidity with a home-brought sensor: Reports 27 C/50% RH (Dew Point = 16 C)
Water temperature is set to exactly 20 C (there's a second dial showing ~18 C but I am unsure if that's the same water supply, I will ask)

Checking the dewpoint PSU with a multimeter shows a voltage of 16 V.
The PSU itself is rated for 12 V output, and the humidity sensor expects 24 V.
Regardless of which voltage 16 V seems incorrect. Might be causing issues.

Humidity is a bit lower now (4pm) the sensor has been in all day, 28 C/35% RH (Dew Point = 11 C) which isn't an issue.

Water is still off until I am sure what to do, or until the dewpoint sensor stops complaining.