Re: Tri-cocks, Tri-cocks, Tri-cocks! - NOT!!

The point is that try cocks do lie, and too many operators think the try cock cannot or will not lie to the operator.
Probably FRA was referring to the fact that if a neophyte operator is not fully cognizant of the fact that the try cock can lie to him, he will become reliant upon the faulty readings the try cock is giving him. That arguably might be OK if the boiler water level is at or near where it should be. However, try cocks are typically resorted to when the water level is in the very bottom of the glass or out of sight in the glass, and that is when it's the most dangerous to rely upon them. The person who does rely on them in that type of situation had damn well better know what he is doing.
And the bigger the boiler, the higher the pressure and the farther the valve is opened, the bigger the error will be in the "presumed" water level based on try cock readings alone. That is NOT a good situation, nor is it one to be either condoned or encouraged.