True, and the current-carrying of the cable is that current deemed to raise the conductor temperature to that "temperature rating" of 70°C (for given installation method and environmental factors). The CCC 'correction factors' ("Ca") for ambient temps above 30°C (table 4B1 in BS7671) indicates that, for a 70°C thermoplastic cable) the tabulated CCC has to be halved at an ambient temp of 60°C. The table goes no further than that but, at least in theory, the CCC should fall to zero if the ambient temp is 70°C.Also, what temperature do you run the heating at ? Older systems regularly ran at 70˚C or higher - and that's the temperature rating of the cable IIRC
Having said that ...
I have certainly experienced T+E cable that he been 'wound around' CH pipes for decades without apparently having come to any harm.I see many houses with standard PVC cables sharing/close to/wound round heating pipes without any issues. Not best practice, but sometimes there’s no option....
Kind Regards, John