Aquastat controls

Joep_2

I understand the function of the upper limit and lower limit controls of an aquastat on a boiler. What does the differential control do?

Unknown

Aquastat

what make & model # is it?
On some units it controls the circ operation.

Dave

Dale

Good question

As the other post suggested the model will tell you a lot about what HW thinks the control differential does. Take a look off the wall for the George L. firedragon discussion of the triple aquastat. All aquastats have a differential, some are fixed, like 10 degrees. Some you can set. Boilers are not nano second computer chips, the on/off of the burner needs to have a delay, a temperature differential is one way to get that delay. If the boiler goes to 180 and there's a large water volume we may want it to pump till it gets to 160, but maybe only 170. Adjustable differentials give the designer a chance to optimize individual systems.

Alan R. Mercurio_3

For the basic/common control here's the scoop.

OPERATION of the Tripple Aquastat


High Limit Controller:


The high limit opens and turns off the burner when the
water temperature reaches the set point. The high limit
automatically resets after the water temperature drops
past the set point and through the 10°F (6°C) differential.

Low Limit and Circulator Controllers:

On a temperature rise, with the adjustable differential at the minimum setting of 10°F (°C), the burner circuit (R-B) breaks and the circulator circuit (R-W) makes at the control set point. On a temperature drop of 10° F (6°C) below the set point, the R-B circuit makes and the R-W circuit breaks.

At any differential setting greater than 10°F (6°C),
the R-B make temperature and R-W break temperature will remain the same (control setting minus 10°F (6°C). The R-B break and R-W make temperature will be the set point temperature plus the difference between the differential setting and 10°F (6°C).

EXAMPLE:Set point of 140°F (60°C) differential set at 25°F
(14°C). On a temperature rise, R-B will break and R-W will
make at 155°F (68°C). On a temperature fall, R-B will make
and R-W will break at 130°F (54°C).

On the L8124M, the burner and circulator circuits are
controlled separately.the low limit controls the burner circuit(R-B) as described above, while the low voltage thermostat directly controls the circulator circuit Setting:

Follow the boiler manufacturer recommendation when making
the L8124 settings. The high limit setting must be at least 20°F(11°C) higher than the low limit setting. Place the indicators over the selected temperature marks. The low limit differential is set by turning the differential adjustment knob to the desired amount of differential.

I hope this has been helpful


Your friend in the industry,
Alan R. Mercurio

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