Patterson-Kelley TBIG-03 - Manual (Page 18)

Gemini™ Twin-Fuel Gas-Fired Boiler
In the case of the twin-fuel boiler, the phrase “main
gas cock” or “main gas valve” as used in the “Installa-
tion and Owner’s Manual” applies to the manual shut-
offs for both the natural gas and propane supplies.
7.2 S
EQUENCE OF O PERATION
Status (red and green) indicators located on the front
of the control panel of this boiler are specifically de-
signed to indicate the sequence of operations and the
cause of common problems. Careful observation of
indicators should provide a guide to most operational
conditions and problems.
Refer also to the wiring diagrams in Section 8.
The sequence of operation for the twin-fuel model
differs slightly from the standard model:
1. When the On/Off (main power) switch is turned
on, a green indicator marked "Power" or the am-
ber switch is illuminated. Power is applied
through a series of normally closed limit switches,
including water flow, gas pressure, and high tem-
perature, and through the operating temperature
control to the flame-safeguard programmer.
2. The water flow limit switch is closed when there
is adequate water flow through the boiler.
3. When adequate gas pressure is available, the low
gas-pressure limit switch is closed. Manual reset
is required following conditions resulting in low
gas pressure.
4. If the temperature sensed by the high-limit tem-
perature control is below the set limit, the nor-
mally closed position of the switch sends power to
the operating temperature control. Manual reset is
required following conditions exceeding high-
temperature limit. The limit series is complete
unless an external control is placed ahead of the
water flow limit (replacing the red jumper wire).
5. When heat is required, as indicated by outlet water
temperature, power is applied to Terminal 6 of the
programmer, which initiates the burner operating
sequence, and to an indicator marked "Heat."
6. The programmer first energizes Terminal 4 which
supplies power to the contactor for the blower mo-
tor and the air flow switch, which initially shows
low air flow with the "LowAir" indicator. This
indicator will remain on until sufficient air flow is
sensed.
7. A time delay of 10 seconds (standard) or 30 sec-
onds (depending on insurance or local code re-
quirements) occurs after the air proving switch
closes and the programmer signals a continuation
of the start sequence. During this time period the
combustion chamber is pre-purged to eliminate
any residual combustible gas or combustion prod-
ucts.
8. A 10-second "trial-for-ignition" period is initiated
with both Terminals 10 and 8 being energized.
Terminal 10 of the programmer powers the igni-
tion transformer and the "Ignite" indicator. The
transformer output creates a spark at the igniter.
Terminal 8 powers the pilot gas valve and the in-
dicator for "Pilot."
9. When a pilot flame is detected by the flame rod, a
signal is sent to Terminal F in the programmer.
Terminal 10 is de-energized shutting off the spark
ignition and the pilot remains on for ten seconds
during the flame establishing period.
10. After the flame establishing period, Terminal 9 is
energized, which opens the motorized main gas
valve and the motorized gas valve to the fuel sup-
ply in use and lights the "Main Gas" indicator.
The boiler fires. After ten seconds, Terminal 8 is
de-energized and the pilot valve and indicator
light are extinguished.
An auxiliary panel prevents the motorized gas
valves for natural gas and propane to be open at
the same time.
Lo-Hi-Lo: When Terminal 9 is energized, the Lo-
Hi-Lo valve will be maintained in the low fire po-
sition for "low fire start" for ten seconds. If the
operating temperature control calls for high fire,
the programmer will initiate high fire (Terminal
21) at the same time the pilot valve and indicator
is de-energized.
A power failure during operation closes all motor-
ized gas valves and shuts down the boiler. When
power is restored the controller recycles to Step 1;
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