starting problem

Hi all

My skoda has recently started playing up. Its a 1.9tdi pd 2005 model. When starting the car it will not start until the glow plug light shows. I have recently been waiting up to an hour before it even showed. If it dosent show the car will just churn. My mechanic seems to think its the ( engine coolant heater relay ) and put it on a snap on computer and the fault code p1601 showed. I have phoned skoda and they are trying to sell me a coolant sensor. Does anybody know if there is a relay for the engine coolant heater. Ive changed all growplugs recently and that didnt help. Thanks guys