Patent ID: 8669017

Claim:
A method for checking the tightness of a stack of fuel cells, said stack comprising: a plurality of fuel cells, each having a first chamber, a second chamber and a membrane separating the chambers, a fuel feed channel and a fuel discharge channel connected to the first chambers of the fuel cells, and a feed air channel and an exhaust air channel connected to the second chambers of the fuel cells, wherein the first chambers or the second chambers are connected to a tracer gas source and at least one of the channels of the respective other chambers is connected to a gas sensor responsive to the tracer gas, and wherein the gas sensor comprises a lance provided with a sniffer probe, which lance is inserted into a respective channel and is moved therein in the longitudinal direction of the channel, and, upon a response of the gas sensor, the position of the sniffer probe in the channel is determined so as to thereby localize a leak.