That's the same part number I've found.
https://www.ebay.co.uk/itm/134839609703?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=mHShiJT5Ts2&sssrc=4429486&ssuid=IE07kO4STZy&var=&widget_ver=artemis&media=COPY
So sorry to hear about this Steve I know how it feels as the same thing happened to my wife's astra (also electronic handbrake) on our wedding day! It rolled off into another car ina carpark as she went in to get her flowers.
I'd recommend a diagnostic check to see if any fault codes flag up.
Could be an issue with the heater matrix or with the heaters temp sensor etc.
Also is the engine temperature normal (90 degrees). If not could the thermostat be failing?