They used an open one in which the gases that evolve at the electrodes may escape into the air and could not be counted in the heat budget. Overall, the two scientists did not use the proper equipment and correct procedures in their experiment to achieve cold fusion. That is why their experiment is unable to be duplicated. Those who tried to duplicate the experiment got none of the effects that Fleishmann and Pons had claimed they did. No one reported fusion.
Reliability occurs when the study can be reproduced and have consistant results.
Both internal validity and reliability proved to major factors in Fleishmann's and Pons' research. First, the neutron counter they used, the BF3, was very sensitive to heat. This was proven by the team at Georgia Tech. After this news was made public, Fleishmann and Pons emphasized the amount of heat they recorded. It is doubted that they did the necessary stirring based on their set up.