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).

Cause 1: Bad solder joint

I've seen one pair where the solution was to simply resolder the thermistor onto the PCB. It seems GHD decided to stop using the neat little screw crimps, as seen in the GHD Mk3's, and save some cash by soldering instead. Unfortunately some of the solder joints are not great!

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). 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!