replacing an appliance would not normally require the complete wiring to be upgraded, unless say the new wattage is higher or the cable looks distressed in some way, so long as you are not making anything worse and it is not currently dangerous.  - what paperwork are you issuing to cover the job? is there anywhere you can note that there is no RCD but it might be considered as a future improvement ?

Mike.

Be aware, most storage heaters need a full time supply now, not just the 'Economy 7' overnight tariff. This change came in at least 5 years ago, and was to ensure the heaters were as efficient as they can be, they now contain timers and fans to make them slightly more efficient than the old passive heaters that heated up overnight then gave that heat out throughout the day, with the only control, on some, being a damper that closed off the air flow, but in reality didnt do much at all.

www.electricradiatorsdirect.co.uk/.../

No.

Where would you put the RCD if you had to fit one?

As a general principle, as far as installation is concerned, new regs only apply to new work - just the new work, not the rest of the circuit, not the rest of the installation.  On occasions that might mean that some of the existing installation may need improving to allow your new work to comply (e.g. for an extended circuit to have an adequate Zs, or bonding to be present, or acceptable voltage drop). Sometimes improving some aspect the existing is a simpler and neater way of achieving compliance for the new (e.g. swapping an MCB for an RCBO at the start of the existing circuit rather than inserting an RCD as the start of the new work) - but that's an individual design decision, rather than a requirement of BS 7671.

There is an urban myth that any work on a circuit requires the entire circuit to be brought up to current standards - but nothing in BS 7671 demands that - and that sort of thinking quickly ends up getting silly - e.g. having to oversleeving every existing red/black existing connection with brown/blue (or green with green/yellow for even older installations) ... the sort of thing that Dr Johnson would describe as "like fitting wheels to a tomato - time consuming and completely unnecessary".

   - Andy.