Zanussi ZX99/5S - Temperature Alarm

Hi Forum,
I wonder if anyone can help.
I've got a Zanussi Fridge/Freezer that is a good 5+ years old but is a great size and has always served us well.
A couple of months ago the over temperature alarm started going off and the fridge started getting warmer. I checked around and found that the Refigerator Conveyor Heater was melted! I contacted Electrolux/Zanussi and got a replacement through them. I fitted it and all was OK for a few weeks.
Unfortunately, the overtemp alarm still keeps going off every few days and the fridge keeps warming up. If I unplug the appliance for a day and then plug it back it all seems well again for a day or two and then the alarm goes off again.
I've checked the usual like ice build up etc but I can't seem to find a problem anywhere.
Has anyone got any suggestions?
Hope the forum can help.
Regards,
Bill :rolleyes: