There are some EPRI papers on the subject. As I recall, there was a buzz of research on that topic about 20 yrs ago.
If the unit is a high pressure boiler ( MCR drum pressure approx 2800 psig) much of the phosphate will precipitate out of solution onto the hot inside surface of boiler tubes if the tube wall temp is above ( 650 F ?). If the boiler is cycled to low pressures at night , the tube wall temperature and the boiler water saturation temperature drops below 600 F, such that the solubility of phosphate increases and the deposits on the tube surface will return to being dissolved in the boiler water. Tis then raises the phosphate concetraon well above the optimum, and forces teh operator to blowdwon large amounts of water to correct the phosphate ratio.
If you are having alot of problems with hideout, you have a dirty boiler. Just like Dave wrote.
Hideout can be a precuror to corrosion fatigue, Hydrogen damage, acid phophate corrosion and caustic gouging. The last three take place in the high heat release zones.
Corrosion fatigue can be catastrophic failures if located in bends.
