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P/N HN-IOM-1 82-0331 Copyright 2009 Mestek, Inc.
Finned copper tube gas boilers & water heaters – Control manual
Menu item
Under . . .
Explanation
PROOF TIME
AUX FUNCTIONS
COMBUSTION AIR
DAMPER
Set proof time long enough to be sure the combustion air damper can open and activate its
end switch.
RUN IN LOCAL IF:
H-NET COMM LOST
AUX FUNCTIONS
FAILSAFE MODES
When set to NO, the boiler will only operate if activated by an override input (AA, 4-20mA
enable, or T1/T2).
When set to YES, the boiler will revert to LOCAL operation, controlling its outlet water
temperature to the LOCAL SETPOINT setting. The LOCAL PUMP relay will be set to always ON
during failsafe operation.
NOTE: The control will wait 10 minutes after losing communications with the HeatNet master
before switching to local operation.
RUN IN LOCAL IF:
LOW TEMP:
AUX FUNCTIONS
FAILSAFE MODES
This function can automatically start the boiler (or boilers, via the Master) if water
temperature drops below the value set for TEMP LESS THAN. This function can be used to
provide automatic freeze protection. The LOCAL PUMP relay will be set to always ON during
failsafe operation.
Once the temperature (TEMP LESS THAN value) is reached, the boiler (or boilers) will shut off.
Select which sensor to monitor: SUPPLY, RETURN or HEADER.
RUN IN LOCAL IF:
TEMP LESS THAN
AUX FUNCTIONS
FAILSAFE MODES
Set the minimum allowable temperature for the location selected in LOW TEMP, above. The
LOCAL PUMP relay will be set to always ON during failsafe operation.
ALARM TYPE
AUX FUNCTIONS
HEAT EXCHANGER
This setting determines the way in which the control reacts when the differential temperature
across the heat exchanger exceed the specified maximum differential temperature. The
default alarm condition is a WARNING. The WARNING state will allow the boiler to keep
functioning and display a warning message a a timestamp in the status screen when the
maximum differential temperature is exceeded. If FAULT is selected, the boiler will shut down
and act as if an interlock has tripped. After the Delta T has dropped by 10°F, the boiler will
restart if the demand is still present.
EXCHGR DELTA
AUX FUNCTIONS
HEAT EXCHANGER
This feature is active if LIM->HALF RATE is set to YES (see following explanation). When the
temperature rise through the boiler (SUPPLY minus RETURN temperatures) rises higher than
the value of EXCHGR DELTA, the control immediately begins limiting the boiler firing rate to
one half of the called for rate. This quickly reduces the boiler output to avoid short cycling on
limit. The control will return to normal operation once the boiler temperature rise reduces to
10°F less than the value set for EXCHGR DELTA.
LIM->HALF RATE
AUX FUNCTIONS
HEAT EXCHANGER
Set this feature to YES to cause the control to automatically reduce the boiler firing rate to
one half the called for value if the temperature rise through the boiler exceeds the maximum
value desired. This maximum temperature rise is EXCHGR DELTA. NOTE: This function can be
used to prevent short cycling if the header temperature can drop quickly, causing the boiler
to try increasing boiler supply temperature to meet the apparent demand increase. Quick
header temperature drop can occur, for example, when boilers are equipped with slow-
opening valves — the valve begin to allow flow as they open, but the boiler can’t fire until
they are fully open and make their end switches.
NOTE: DISPLAY — When this feature is enabled, the display will be differently from normal.
In RUN mode, the display will show “1/2 INPUT *” instead of RUN %. The “*STATUS” screen will
show “ADAPTIVE IN” over the START and STOP times.
DHW BOILER?
DOMESTIC HOT WATER
Setting this value to YES enables the boiler/system for DHW operation. DHW settings are only
looked at if this is set to YES.
DHW SETPOINT
DOMESTIC HOT WATER
The setpoint that the boiler/system will target. The boiler shuts off when this temperature is
reached.
DHW DIFF
DOMESTIC HOT WATER
This is the amount the temperature must drop below the DHW SETPOINT to start the boiler.
USE SENSOR?
DOMESTIC HOT WATER
If this entry is set to YES, the HeatNet control monitors the DHW 10k sensor and regulates the
boiler to achieve the DHW SETPOINT.
DHW PRIORITY?
DOMESTIC HOT WATER
If the DHW PRIORITY is set to YES, then when there is a call for DHW, the system pump shuts
off. If set to NO, the system pump stays on.
Table 9
Setup menus — parameter explanations (continued)
Control menus and adjustments
(continued)
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