Possibly a failing switch
http://www.buyspares.co.uk/cooker-oven/ec600dodlm-058552065/energy-regulator-simmerstat/catalogue.pl?shop=stoves&path=110835&model_ref=1014532&refine=energy%20regulator%20%28simmerstat%29
Check you are ordering the correct part
Make sure you know how to change the part
Make sure you are competent to do so.
XXX
June 2016