Harry Ciechanowsky asks:

If one lives in a flat (all Jewish) which has the eiruv chatzerah, and he goes away for shabbos, and the flat is locked, is the eiruv valid?

The Kollel replies:

The Mishnah on Daf 86a, cited also on 47a, discusses an argument among the Tana'im as to the status of an apartment whose owner is not home, and whether the remaining house owners may carry in that Chatzer.

However, that discussion only pertains when the owner of the unlived-in house did not contribute to an Eruv Chatzeros with the other houses (see, for example, Mishnah Berurah O.C.371:1). If he did create an Eruv with the others, they certainly may carry even when he is not home.

Be well, Mordecai

Yossi Fromer points out:

I think the question asked by Harry was Why is it different to a case where he lost the key (Eruvin 34b) and the eruv is not an eruv? This also applies to eruv chatzeros. (Din 394) If someone who has the eruv in his own home goes away out of town for Shabbos and his place is locked Why is the eruv an eruv?

The Kollel replies:

Thank you! In the case the actual Eruv itself (the food that comprises the Eruv) was placed in the flat of the person who went away, the answer is as follows. The purpose of the Eruv is that all the tenants of the Chatzer are united in one home where their food is located. If they have no possibility of accessing the food of the Eruv on Shabbos, then the Eruv is indeed invalid. A possible solution would be to leave a key with a neighbor who could allow access to the Eruv-food in the event that someone wished to eat it.

Ilan Segal