Why is the light staying on, on my electric hob,when not being used?

Hi,

I have a electronic hob with four plates.

Since yesterday one of the lights that comes on to tell you a plate is hot, will not go out - it just stays on continuously. the other 3 are fine, it only affects the bottom left light!

the only writings on the hob I can find are "pro line" and "euro kela" but no numbers etc

Anyone know why just one of my lights is staying on, even after the plate has cooled down??

Many Thanks in advance

Chris