Do i need to rewire or upgrade consumer unit for EICR??

[JohnW2]

The electronics in a timer fan would conduct when you apply an IR test voltage - you'd need to use 250V rather than 500V. Between L&N would attempt to power up the timer, between SL and N would create a path through the electronics, as would SL to L.

Yes, on reflection you're right.

It's worth testing with both polarities in case there's any diodes/half wave rectifiers in the circuit.

I don't think it's really a matter of "in case" since I've never seen a fan timer module which did not use half-wave rectification (i.e. just one diode) and, furthermore, the diode would be in opposite polarity for the paths through electronics) from L to N and from SL to L- so testing with both polarities would probably be essential.

Kind Regards, John