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MODGAS-XWR2-B Technical Guide
SEQUENCE OF OPERATION
Valve Failure, Force Mode and Master vs. Normal
Valve Failure
If a valve failure occurs, the board fails that stage and then continues
to the next available stage. This is to make sure that if there is a call
for heat, heat is being supplied. A valve failure consists of either a
Valve No Detect or a Proof of Flame Fail.
1V1IGN1S/2V1IGN1S:
If the modulating valve fails, Heat 1
(RLY3) is turned off and the board then moves to the fixed stages
(if available). If the valve fails when there is first a call for heat,
then the first fixed stage will come on immediately. Every ignition
retry period (set in the hidden configurations menu), the board will
re-attempt to detect the valve(s) and retry the ignition process.
2V2IGN2S:
If the first stage (the first modulating valve) fails when
there is first a call for heat, Heat 1 (RLY3) is turned off and the board
immediately moves to the second stage (the second modulating
valve). If the first stage fails when the board is in MODULATE_
MODE, then normal board operation continues.
If the second stage fails, Heat 2 (RLY4) is turned off and the board
continues normal operation and moves to the next fixed stages.
Every ignition retry period (set in the hidden configurations menu),
the board will re-attempt to detect the valve(s) and retry the ignition
process.
Force Mode
This mode is used to test that the valve firing sequence is functioning.
This mode is NOT meant to replace heating mode by any means.
There is no staging in this mode, and there is no PID Loop running
in this mode. Once a stage is forced on through the Force Screen,
the board will enter Force Mode and will not leave this mode until
all the stages that were forced on have been turned off or 10 minutes
pass with no user input to the board.
The following options are the Force Mode configurations.
1V1IGN1S:
Forcing Stage 1 on forces Heat 1 (RLY3) on, and then the
next screen allows the option to decide the modulation percentage
for the valve. Forcing stages 2-4 on forces Heat 2-4 (RLY4-RLY6)
on, respectively.
2V2IGN2S:
Forcing Stage 1 and 2 on forces Heat 1 (RLY3) and
Heat 2 (RLY4) on, respectively, and the screens following each force
screen allow you to select the percent modulation for each valve.
NOTE:
Configuring one stage below the low speed cutoff
and the other above it will cause combustion fan low
speed relay (RLY2 - LOW SPEED)
difficulties.
Forcing stages 2-4 on forces Heat 2-4 (RLY4-RLY6) on.
2V1IGN1S:
Forcing Stage 1 on forces Heat 1 (RLY3) on, and the
next screen allows the option to select the modulation percentage
(since both valves are one stage, they both modulate at the same
percentage). Forcing Stages 2-4 on forces Heat 2-4 (RLY4-RLY6)
on.
2V2IGN1S:
Forcing Stage 1 on forces Heat 1 (RLY3) and Heat
2 (RLY4) on, and the screens following allow you to select the
modulation percentage for the respective valve. Even though both
valves are considered one stage, since they operate on separate
relays, the option to modulate them at different percentages is
available.
NOTE:
Configuring one stage below the low speed cutoff
and the other above it will cause combustion fan low
speed relay (RLY2 - LOW SPEED)
difficulties.
Forcing stages 3 and 4 on force on Heat 3 (RLY5) and Heat 4
(RLY6), respectively.
Master vs. Normal
In order to help clarify operating modes, master and normal are
used to denote two MODGAS-XWR2 series boards that are
communicating with one another. With one MODGAS-XWR2-B,
the maximum number of modulating valves is two, but with two
boards the maximum is four (two for each board). In a master/
normal operation, the secondary board is slaved to the master board.
•
To configure a master board, put the “S/A MODE” for
the board to “FORCED” and put “OPERATION” to
“MASTER” (both configurations found in the hidden
screens).
•
To configure a secondary board, put “OPERATION” to
“NORMAL” (found in the hidden screens).
The following options are the Master/Normal configurations.
2V2IGN2S:
In this configuration, both boards utilize both heat relays
for a modulating gas valve. Stage 1 is the valve attached to Heat 1
(RLY3) for both boards, and Stage 2 is the valve attached to Heat
2 (RLY4) for both boards. The valves on both boards are always
modulated to the same position, and both boards stage up (i.e. turn
on Heat 2 (RLY3)) at the same time.
2V1IGN1S:
In this configuration, both boards utilize Heat 1 (RLY3)
to turn on two modulating gas valves (a total of four for the two
boards). This means that each board has an open relay (Heat 2
(RLY4)) for an additional on board fixed stage. The two valves
on both boards (i.e. all of the four valves) are always at the same
modulation position. The first stage up (i.e. Stage 2) will energize
Heat 2 (RLY4) on the master board, and the second stage up (i.e.
Stage 3) will energize the Heat 2 (RLY4) on the secondary board.
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