A faulty thermostat won't set a light. However, once I had a light which was for the temperature sender/sensor. It only happened once and it switched off the light by itself when the glitch cleared. If the ECU thinks the temperature sensor is faulty, it will switch the fan on continually to make sure the engine doesn't overheat (since if can't rely on the reading), which will keep your engine temp low. (Note that in Alfa's wisdom the sensor is actually a pair - one for the ECU and one for the interior gauge - so the gauge could be reading fine, but the ECU is getting the wrong numbers). So, it would be worth checking if the fan is running all the time even when cold.
Speaking from experience, if you can get hold of a VAG-COM cable (£20-25 eBay) and a freebie copy of FiatECUScan on a laptop, it's worth the investment! If it turns out to be the temp sensor, I recently had a price of about £10 from Alfashop and it looks like it should be simple to swap.
The light has come on more than once, on two consecutive days, and the light hasn't come back on since Tuesday. You could be right saying the engine temperature sensor, but when it first happened I did check to see if the fans were staying on, but they did cut out when the optimum temperature was reached, and the light was on at the time.
The car is booked in at Go Italia on Wednesday to have her plugged in, so should hopefully show up the fault.
I have just thought, i'm wondering if it could be to do with the battery? Only not long ago, i had a problem starting the car as the negative lead was loose on the battery terminal, and wondering if it has come undone again,but maybe coincidence. Would resetting the ecu possibly clear the glitch?
Marky, the first day you phoned me and told me the light was on you where concerned the car was overheating because the fans where on constantly. Where the fans on the other day when it did it? you have also reported that your heat gauge doesnt always warm like it should as well? if you had a phase one you cant miss the double fans when they kick in
I haven't noticed the fans being on all the time, but definitely worth checking out again
Yes, the heat guage doesn't go up at all now, just sits at cold all the time, she is not being very warm to me at the mo lol
I'm very jealous of your double fans lol