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Mrbiccies . . . . . .
From the sacrosanct words of Weller . . . . . .
The use of precision Platinum (RTD – Resistance Temperature Detector) Sensors (WP80 / WSP80 / WMP, etc.)
in the Soldering Handpieces, constitutes extremely long life while providing highly accurate temperature readings.
( Now doesn't that statement just warm your heart and think that the sensor PROPER is possibly NOT being the fault, since there is / are also interconnected wiring and interfacing connections !
Hows about disassembling that unit, in order to get closer access of the inner temp sensor element and see if you can then individually "ohm out " between its two external connecting wires and the furthermost point that you can get to, within the unit, towards the units frontal platinum sensor.
Considering its high temperature environs, they must have used either a crimp connection, a micro SILVER solder connection or a spot weld for their connection interfacing.
Initially, was your testing of the "found" high resistance ( 1K+ . . .vice . . . approx 22 ohms) reading for the sensor being made at ITEM 7 connector or its connecting mate at the soldering station proper ?
If so . . . . . retest at the Blue / or / Brown paired connections at the bottom pic of my illustrations.
I don't know if this was being your iron from purchase day one or if it was an acquired used item, possibly coming from a production line.
It is a known fact that a heavily used unit can develop metal flex fatigue of its internal wiring at repeated bend/stress points
Soooooooooo after 'bouts eight tousands fo 'hunnerts and 'lebenteen times . . .thereabouts . . . an open wire connection can develop.
See if this just might be your lucky day.
If not . . . . .
Referring to the illustrations :
Differentiate between the Brown or Blue set of wires as to which is the heater wires and which are the sensor wires.
Initially see if the sensor wires might just slowly pull out or, if they are being taut.
Then see if working with inspecting A or B mechanical area might permit a further dis-assembly of the unit, for seeking out its interconnect wiring.
ZUJ'ing
73's de Edd