3 Indirect Thermostat T12 Negative feedback for linear output 5 to 30 psi air orgas supply pressureStainless steel housingBi-metal sensing elementfor accurate controlSingle adjustment overWide temperature range:T to 400oFHT to 700oFOutput pressure proportionateto temperature at any settingT12
4 ? Direct or Indirect ? Direct Mode Indirect Mode Rising Temperature Rising TemperatureRising Output Falling OutputDirectIndirect
20 Trouble Shooting SYMPTOM CAUSE Bent sensing element Erratic temperature changesContinuous ventingBent sensing element(element should be centeredin base and should “ring”)Incomplete immersion of probeDirty pilot plug seatHole in diaphragmWeak pilot plug springFaulty ‘O’ ring
21 Trouble Shooting To check small seat: increase temperature setting several degrees and see if venting stops.To check large seat: decrease temperature settingReplace pilot plug and seats if unable to stop ventingby cleaning seats.