TL;DR

Temperature deviation is usually a failed heating element, a blocked heat exchanger, or a thermocouple calibration drift. Check the heating system and sensor calibration before adjusting the recipe.

What you might see

dye bath temperature not reaching set-point
temperature alarm during the dye cycle
uneven dyeing or shade variation across the batch
heating time longer than normal

Likely causes

Tap to mark as ruled out

Heating element scale buildup or failure reducing heat transfer to the bath
Steam heat exchanger fouled with calcium deposits reducing heating capacity
Temperature sensor (thermocouple or PT100) calibration drift or failure
Steam supply pressure below specification reducing heat input

Required tools

Calibrated reference thermometer
Steam pressure gauge
Descaling chemical approved for the heat exchanger material
Clamp ammeter for element current check

Safety first

Dye baths operate at temperatures up to 140 degrees C under pressure. Follow the depressurization procedure before opening any vessel lid or access port.
Descaling chemicals are corrosive. Wear acid-resistant gloves, face shield, and chemical-resistant apron during descaling.
Steam supply lines are under pressure. Isolate and bleed steam pressure before disconnecting any steam fitting.

Procedure

7 steps · ~90 min

1
Compare the actual bath temperature reading to an independent calibrated thermometer placed in the bath. A discrepancy of more than 2 degrees C indicates sensor drift.[1]
2
Calibrate or replace the temperature sensor if it fails the comparison check.
3
Check the steam supply pressure at the heat exchanger inlet against the specification. Low steam pressure requires investigation of the steam supply system.
4
Inspect the heat exchanger for scale or fouling. Run a descaling procedure if the water hardness log shows untreated hard water use, or if the heat transfer rate has declined.[1]
5
Check the heating element current draw if the machine uses electrical heating. Low current indicates a failed element.
6
Verify the bath circulation pump flow rate. Reduced flow from pump wear or a blocked filter will cause temperature stratification in the vessel.
7
Run a water-only trial cycle after repairs and log the temperature profile against the control recipe. Accept the machine when the actual temperature tracks the recipe within 2 degrees C.

Sources

Thies Thies iMaster H2O Dyeing / Finishing Range general technical documentation, Thies
Thies iMaster H2O dyeing machine general temperature control and maintenance procedures (general)

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