Aqua-stats
Immersion Type
 A threaded well is immersed into boiler water
o Bulb sits inside the well
 24V or 120V N/C
 SPST or SPDT
 Maintains boiler water temperature 180ºF to 200ºF
o Triple aqua stat comes preset 180 ºF
 Fixed differential 10º or adjustable differential
 Contacts open on temperature rise (high limit)
 Contact closes on temperature fall (high Limit)
o Ex: set at 180º = opens at 180º and closes at 170º (differential)
 Also used as a high limit(operating control) N/C to break the circuit to
the oil burner or gas valve when water reaches desired cut out 180ºF
-200ºF contacts open on temperature rise
 Also can be used as a reverse acting control (N\O) to turn on
circulator or unit heater
o Closes on temperature rise
 Also can be used as a low limit
 Can be either a single Aquastat or a triple Aquastat
o Triple Aquastat : controls burner circuit, circulator and a high
limit (safety)
 B1& B2 = burner circuit( can be either 24V or 120V circuit
depends on type of Aquastat)
 C1 & C2 = circulator(L1 and N)
 L1 & L2 = hot in and neutral
 T and T(or TV)= to end-switches or thermostat (energizes
relay for circulator circuit)
 G=ground
Surface Mount or Strap on Type
 Attached to the pipe and senses the temperature of the pipe not the
water directly
 Works same as immersion type
 For hydro coil or fan coil units set at approx. 140ºF to turn a fan on
 Opens on temperature rise
 Closes on temperature drop
 SPST switch N\O