Hi i contacted support and recieved this
Thanks for your email and I'm sorry to hear about this issue.
Sometimes temperature issues are caused by calcium build up or corrosion on the part of the device that touches the water. Please check if the heating element, probe, and impeller are all clean.
If the issue will persist, please let me know.
I was surprised at response as a quick google search gave me pages of people with same problem
I replied straight away explaining problem was persisting and no response. I replied again 3 hours
later and now we are into another day without any joy or response