This has to do with my oil fire burner. I have baseboard heat in my house; 4 zones using Taco zone valves; a Taco circ on the return line before entering the oil burner; on demand coil in oil burner. It has a Honeywell 8151 triple aquastat. The high set-point is at 180, the low set-point is at 160 for DHW. My problem is after the oil burner has run for a few minutes due to a zone calling for heat or keeping the water temp from falling too far, I notice that the water temp will go above 200 degrees before the oil burner off. If the water temp is above 200, the oil burner will still fire up even with a temp over 200 degrees. Thinking the temp guage may be faulty I changed it but it made no difference. So, now I'm wondering if the well into which the aquastat bulb sits is corroded to the point that the bulb on the aquastat is getting a faulty reading or perhaps the triple aquastat itself is faulty and needs replacing. Can anyone offer any suggestions (other than calling plumber) or know of some trouble shooting techniques I can use to narrow down the problem? Thanks. Roger