Differential (Hysteresis) Settings; Space Heating Differentials; Setting “Off” Differential - Weil-McLain ULTRA ULTRA-105 Service Manual

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GAS FIRED WATER BOILER SERIES
See Figure 25, page 42 for procedure to access Parameter settings.
Parameter explanations

Differential (hysteresis) settings

DO NOT change the differentials (hyster-
esis) for DHW operation (parameters 24
25, 26 and 27). Always use only the factory
default settings for these parameters.

Space heating differentials

(parameters 22 and 23)
1. The term, "differential," is also referred to as "hys-
teresis."
2. Parameter 22 is the "ON" differential. The water
temperature must be at least parameter 22 less than
the calculated setpoint temperature for the boiler to
turn on.
3. Parameter 23 is the "OFF" differential. When the
boiler is firing, the water temperature must rise at
least parameter 23 above the calculated setpoint
temperature for the boiler to turn off.
Space heating on and off differentials (hysteresis) — Parameters 22 and 23
Part number 550-100-029/0810
—
1 & 2
(continued)
4. See Figure 31 for an explanation of the "ON" and
"OFF" differentials of the Ultra control module.
Note that the differentials are greater when a heat
call starts or stops, as shown. The differentials
decrease with time until they equal parameters 22
and 23.
Setting "OFF" differential
(parameter 23)
1. The factory DEFAULT setting for parameter 23 is
4°F. This works well for most applications.
2. For low-mass systems (fan coil), performance can
be improved by increasing parameter 23. This
compensates for the quicker system temperature
response of low-mass systems. Typical settings for
fan coil systems are parameter 23 set at 16°F, with
parameter 4 set at 180°F, to allow adequate time for
the boiler to modulate.
3. When setting parameter 23, make sure that param-
eter 23 plus parameter 4 is not over 203°F to avoid
possible nuisance lockouts.
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