Thermistor Repair

GHD Mk4 straighteners use an NTC (Negative Temperature Coefficient) Thermistor to regulate the temperature of the heaters. If for any reason the electronics does not get a sensible reading from the thermistor, then you'll hear a continuous beep and they won't heat up.

GHD Mk3's do not suffer from this problem (as they don't have a thermistor).

The thermistor is the brown wires coming heater plate on the non switch side arm:

It should measure 100kOhms at 25degC.

Continuous Beep Cause 1: Bad solder joint

I've seen one pair where the solution was to simply resolder the thermistor onto the PCB. GHD don't use the screw terminals for the thermistor connections to the PCB.

Continuous Beep Cause 2: Broken Thermistor

If the thermistor breaks (i.e. the resistance across it is infinite) then it needs to be replaced.

The best thermistor I have found for the job is a 104GT-1 (datasheet) which is available from Rapid Electronics (part number 61-0452) or our online shop. This is 100kOhm at 25 degC.

When I do this repair I transfer the insulation sleaving from the old thermistor to the new one, and put a small piece of kapton tape around the thermistor's bead. Then you need to glue it down to the heater with a suitable glue (good to >200 degC). I use silcon adhesive (Dow Corning 744). Put it all back together, and with any luck it should work again!

Overheating Problems

If the thermistor becomes detactched from the heater element it is supposed to be measuring the temperature of, then this will cause the GHDs to overheat and trip the thermal fuse. It will be necessary to reattach the thermistor and then replace the thermal fuse.

This page was last updated at 11:32pm on 16th February 2010