Plumber writes:

"As a recent experience of mine in fitting up a double-boiler system may serve to give a useful hint to others or save them a like mistake, I send you an account of it.

" After renewing some plumbing in a private residence here, I turned the tank water on to the inside boiler A only, of the usual double boiler shown in the diagram. Very soon water began to run from cocks connected with the outside boiler B only. Careful search revealed no by-pass, and the inside boiler, though just tested, was declared to leak. When removing it to be retested I found that the sediment cocks C and D were of different patterns, so that when the handles were in the position shown, C was open and D was closed. Supposing both to be like D, I had turned them as shown, hence the trouble.

"This discovery of course solved the mystery, as the water passed through C and filled B as indicated by the arrows C was immediately replaced by a cock like D, when everything worked properly, and no harm was done, except in losing considerable time to find the trouble."