Honeywell International Inc. W8735ER01 Manuale Utente

5

66-1202—01

(design temperature) is the point at which the boiler should be 

set to its high limit setting. Setting the boiler temperature too 

low during the coldest periods will result in the inability to keep 

up with heat demand. This is the critical setting in avoiding 

call-backs.

High Outdoor Temperature: This is the outdoor temperature 

for which the Low Boiler Temperature is set. This is the 

parameter that most impacts energy savings. Setting the High 

Outdoor Temperature too high results in less energy savings 

as the boiler may run at a higher temperature during warmer 

weather than necessary to maintain comfort in the space. 

Setting this parameter too low will result in too narrow a range 

for the control to be adjusting boiler temperature. In most 

cases the default of 40 °F (4.4 °C) is fine.

When enabling the Outdoor Reset function, be sure to 

refer to the boiler OEM’s instructions for the lowest 

return water setting to avoid condensation in the heat 

exchanger, which can result in equipment damage. 

1

Minimum values, Maximum values and Default High Limit 

settings shown are for the L7224U and the S9361 IBC. Val-

ues may change for other Aquastats and IBCs. Check the 

specific Aquastat and/or IBC Installation Instruction manual 

for more information on default settings.

If heat demand is not met within a certain time period while 

the boiler is in setback mode (following the Outdoor Reset 

curve), a Boost Period is invoked where the boiler set point is 

increased by a value called the Boost Step. Each time the 

Boost Period elapses and heat demand is not satisfied, the 

boiler set-point is again increased by the Boost

 Step, up to the 

maximum setting provided by the High Limit setting (see Table 

2 and Fig. 5). Boost is reset when the heat demand is satisfied 

(local or remote call for heating has ended). Simply reaching 

the boiler set-point does not reset the Boost. Continuous 

Boost calls may be an indication of a poorly set Outdoor Reset 

Curve for the environment or faulty equipment. For the 

Aquastat, a Boost warning will be indicated on the 3-digit 

Aquastat display if Boost is required on 60 consecutive cycles. 

See Table 5.

For the Aquastat, the Boost Period can be set from OFF to a 

range of 5 minutes to 30 minutes, adjustable in 1 minute 

increments. The default setting is 10 minutes. The Boost Step 

can be set from Off to a range of 5 F (-15 C) to 20 F (-7 C).

For the IBC, the Boost Period is fixed at 30 minutes and the 

Boost Step is fixed at 5 °F. See Table 2.

 For the IBC, both the Boost Period and Boost Step are fixed 

parameters and can not be adjusted.

The Warm Weather Shutdown feature causes a “Warm Start” 

boiler to shut down when the outdoor temperature exceeds a 

specified value. Warm Start boilers maintain a minimum 

temperature by setting the Low Limit on the Aquastat. If 

enabled this features cancels the Low Limit setting when the 

outdoor temperature exceeds a specified value.

In applications with zoning panels having a priority 

zone for domestic hot water: Disable the warm 

weather shutdown feature on the Aquastat.

The Warm Weather Shutdown feature can be set from OFF to 

a range of 40 °F (4.4°C) to 70 °F (21 °C), adjustable in 10 

degree increments. The default setting is OFF. See Table 3.

High Limit

130 °F

(54 °C)

240 °F

(116 °C)

180 °F

(82 °C)

Minimum Outdoor 

Temperature

-40 °F

(-40 °C)

40 °F

(4.4 °C)

0 °F

(-18 °C)

Minimum Boiler 

temperature 

80 °F

(27 °C)

180 °F

(82 °C)

130 °F

(54 °C)

Maximum Outdoor 

Temperature

30 °F

(-1 °C)

70 °F

(21 °C)

40 °F

(4.4 °C)

High Limit

130 °F

(54 °C)

220 °F

(104 °C)

180 °F

(82 °C)

Minimum Outdoor 

Temperature

-40 °F

(-40 °C)

40 °F

(4.4 °C)

0 °F

(-18 °C)

Minimum Boiler 

temperature 

130 °F

(54 °C)

150 °F

(56 °C)

140 °F

(60 °C)

Maximum Outdoor 

Temperature

40°F

(12.7 °C)

70 °F

(21 °C)

40°F

(12.7°C)

Boost Period

5 minutes 

(or Off)

30 minutes

10 minutes

Boost Step

5 F (or Off)

20 F

10 F

Boost Period

30 minutes

Boost Step

5 F (or Off)