They could have gone into shiver mode, a safety feature used by GHD to prevent condensation/heater damage. Take them to a warmer room/wrap in a towel (turned off) or put on radiator for a couple of minutes. If not it will be either the PCB has failed or heater.
If you require a repair service we offer this for £19.50 with 3 month warranty at www.siriushair.com
siriushair
February 2015
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