I visited Renault to get a price but they, despite spending half an hour on Dialogys and phoning another Renault garage, could not find the part number.
Possibly because they were looking in the wrong place... ?
These thermoplungers can only be bought as a unit - all four in the housing, probably because they know they will be so corroded by the time you need some replacements you would have difficulty getting them out without destroying the whole housing!
The part number is 82 00 000 677
It is in the heating section (61) as they heat the coolant. Unfortunately whilst they are normally called thermoplungers, if you tried to find them in the Espace section of Dialogys by name, they will not show up since someone called them a 'Heating element' on this occasion.
These four heaters are supplied by three relays, one each for two of the relays and the other two by the final relay. This means that you can have one, two, three or four activated depending on which relays are operated.
Ultimately, I really need a part number for the thermoplungers
Now you have it; the last I remember the unit cost about £50 but that was a while ago.
Roy