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P/N HN-IOM-1 82-0331 Copyright 2009 Mestek, Inc.
Finned copper tube gas boilers & water heaters – Control manual
Configuring for DHW applications
(continued)
5
DHW Method 2 —
Tank thermostat control
Tank thermostat located in tank.
❑
One boiler, master or member if in a network, operated
❑
by thermostat closure (across boiler’s OA OVR terminals,
J12A terminals 7/8 — see Figure 4, page 23 for location).
Dedicated water heating or combined space heating and
❑
DHW.
For multiple-boiler applications, it is preferable to use a
❑
member boiler for this purpose. If the master boiler is used,
the system cannot operate both space heating and DHW
concurrently.
Limiting maximum boiler temperature when
applying for DHW applications —
When the
boiler is to be used for domestic water heating,
jumper JPS1 must be clipped. This limits the
maximum water outlet temperature. Failure to
comply could result in overly hot water being
delivered to the system. See Figure 3, page 22 for
location of JPS1.
Method 2 operation
When the tank thermostat calls for heat, closing its contact
across J12A terminals 7/8, the boiler enters DHW heating
mode.
The boiler fires to 100% of maximum input.
❑
The HeatNet control senses boiler temperature, shutting
❑
the boiler off if temperature reaches the OPERATE LIM
setting (in setup menus, SETUP / SETPOINTS). (See
Table 7, page 30 and Table 9, page 35 for information.)
While boiler temperature is below OPERATE LIM minus
❑
OP LIM BAND, the boiler is at 100% of input. (See Table 7,
page 30 and Table 9, page 35 for information.)
While boiler temperature is in the OP LIM BAND, the
❑
maximum firing rate decreases as the temperature rises, un-
til it reaches minimum input at OPERATE LIM tempera-
ture, where the boiler shuts off.
Set the OP LIM BAND as wide as possible to reduce likeli-
❑
hood of short cycling.
Method 2 post purge option
When the tank thermostat opens, the boiler stops firing, but the
DHW relay will remain on for the POST PURGE time set in the
DHW Setup menu.
DHW post purge allows dumping the residual heat in the boiler
to the DHW tank.
Post purge will increase tank temperature
above SETPOINT —
Adding additional heat
to the DHW tank after the tank thermostat
setpoint temperature is reached will increase
tank temperature ABOVE setpoint. Ensure that
this is acceptable. IF NOT, then the pump post
purge must be disabled (set to zero).
Method 2 setup procedure
Wire the tank thermostat DRY CONTACT across the in-
❑
put on J12A terminals 7/8 (Figure 4, page 23).
Clip jumper JPS1(
❑
see Figure 3, page 22 for location) on the
boiler that will be used for DHW.
Wire the DHW pump relay or valve to the normally-open
❑
contact, DHW PUMP/AUX. STATUS terminals, J13 ter-
minals 9/10 (Figure 3, page 22).
On the DHW boiler, navigate to the SETUP / DOMES-
❑
TIC HOT WATER menu.
For DHW BOILER? enter NO (will be changed to
a.
YES only after other parameters are set).
Skip the values for DHW SETPOINT, DHW DIFF
b.
and ADD BOILER DELAY. Just leave set at defaults.
Enter NO for USE SENSOR?
c.
For DHW PRIORITY?, select YES.
d.
Select the desired POST PURGE time (how long the
e.
DHW pump or valve will remain open after the boilers
have shut down). See previous WARNING regarding
pump post purge operation.
For DHW MASTER?, select NO.
f.
Go to DHW BOILER? and select YES. Note that, if
g.
jumper JPS1 has not been cut, the display will show a
message to do so.
