Juts to add that we have checked plug tops, sockets, fuses etc.   Still fail on new kit and not on old model. 

'Polarity' in this sense means the tester thinks that L and N are reversed.

To prove this you could rewire one plug to make a lead where L and N are actually crossed (so connect Blue to the fuse, Brown to the neutral pin) and see if the recalcitrant tester passes it.

Once you have verified this, then put it back properly soonest of course !

If that deliberately reversed lead was a 'pass' that would be the smoking gun that the tester has an internal wiring error.

At which point you present your evidence to the makers and demand they give your money back and if  it looks like more than one affected unit, also issue a product warning or maybe a recall.

Trading standards (via Citizens Advice Bureaux these days) should be interested, but would probably not consider it very serious.

Mike.

If that did prove to be the cause.... it should lead to some very serious internal questions for the manufacturer about their own end-of-line testing!

Yes, of course human error can & does/occur... but there should be sufficiently vigorous testing in place to ensure that such errors are detected & don't leave the factory.

mapj1 said:

At which point you present your evidence to the makers and demand they give your money back and if  it looks like more than one affected unit, also issue a product warning or maybe a recall.

To be fair to FirstStop, I've always found them very good at sorting problems (no hassle, no cost, and very quick), my impresion of them has always been that they are a very small business but with their heart in the right place. Gerard O'Neill (88a10928e0f715c5c41e7b957428dc68)  haven't they suggested that you just return the new unit to them for them to test it?  If not I would be saying to them "I'm putting it into the post to you"!

mapj1 said:

At which point you present your evidence to the makers and demand they give your money back and if  it looks like more than one affected unit, also issue a product warning or maybe a recall.

To be fair to FirstStop, I've always found them very good at sorting problems (no hassle, no cost, and very quick), my impresion of them has always been that they are a very small business but with their heart in the right place. Gerard O'Neill (88a10928e0f715c5c41e7b957428dc68)  haven't they suggested that you just return the new unit to them for them to test it?  If not I would be saying to them "I'm putting it into the post to you"!