Peugeot Boxer key fob.

A couple of things from another forum: Lithium batteries are now (apparently) coated in Bitrex to discourage children from swallowing them, so it may help to wipe them over with a damp cloth to remove the coating. And of course, make sure the battery is up the right way, and exactly the right type (e.g. a CR2025 will physically fit in place of a CR2032, but it often won't press hard enough on the negative contact to work correctly).

It's a bit frustrating that Boxer keys don't seem to have an LED to show when they are transmitting.

Something that I know can happen from personal experience (with a VW key, but I think they all work in the same way): If any of the key buttons fail in a way that the circuit is closed, *none* of the keys will work (it's to do with fact that the keys work on a multiplexed system). So one thing to check: do *all* of the buttons operate with the correct "click" feel?

Note also that the keys and van work on the basis of a list of accepted codes each of which can only be used once, so if the buttons are pressed while out of range more than a certain number of times, it will cease to work and will need re-synching with the van. I've never seen a spec which shows how big the list is, but I think it's probably of the order of 20 - possibly more - though this may also vary by make.

On our key, the cause was a slight distortion of the outer case, which was stopping one of the keys from returning to the outward position.

I know you already have, but please ignore my post above - it doesn't make sense because in two places I used the word "keys" when I should have used the word "buttons". It's too late to edit or delete the post (and it's not possible to report your own post to a mod for deletion).