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18 | TWH-G2-12 | 2400E, 2400EO, 250SX, 250SXO, 635ES, 635ESO
Adjusting CO
2
NOTE: When making adjustments with the front cover off, CO
will be 0.3 - 0.5 % lower than with the front cover on. Make fi nal
readings with the front cover installed.
NOTE: Adjusting P1 CO
levels will change the P2 CO
2
fi rm the P1 value BEFORE adjusting the P2 level.
Adjusting P1 CO
level
2
1. Loosen yellow painted Philips screw and cover should rotate
down revealing a brass slotted screw.
Adjusting P1 CO
level
2
2. Adjusting the brass slotted screw counter-clockwise will raise P1
CO2 levels and clockwise will lower P1 CO2 levels.
Adjusting P2 CO
level
2
1. Remove yellow painted #40 Torx cover from the front of the gas
valve. A plastic #40 Torx screw will be revealed.
Adjusting P2 CO
level
2
2. Adjusting the plastic #40 Torx screw counter-clockwise will
lower P2 CO2 levels and clockwise will raise P2 CO2 levels.
NOTE: These screw adjustments are very sensitive and may take
several minutes to stabilize.
Data subject to change without notice | Printed in the USA | 03.2007
Final readings
1. Verify both P1 and P2 are within the ranges specifi ed in the
levels
table below. Continue adjusting the P1 and P2 levels as necess-
2
sary until CO
Proper CO
levels. Con-
2
2. As a safety precaution, verify the Carbon Monoxide (CO) read-
ings on P1. CO levels should not exceed 300ppm (follow local
codes if more restrictive). If values exceed this limit, inspect
vent system and fi ncoils on the heat exchanger for blockage. To
access heat exchanger fi ncoil, refer to service bulletin TWH-G2-
22.
Proper CO readings
Returning to Service
1. Return slotted cover to original position.
2. Reinstall Torx cover.
3. Remove CO
exhaust collar.
4. Turn ON/OFF switch to the OFF (O) position and then back to
the ON (I)position.
5. Heater is ready for normal operation.
values are within the specifi ed ranges.
2
readings
2
Natural Gas
Max input P1
9.7 ± 0.3 %
Min input P2
9.5 ± 0.5 %
Natural Gas
Max input P1
300ppm
analyzer probe and reinstall brass fl athead screw in
2
BBT North America Corporation
Bosch Group
Bosch Water Heating
340 Mad River Park
Waitsfi eld, VT 05673
Telephone 800-642-3111
Fax (802) 496-6924
techsupport@boschhotwater.com
Service bulletin
LP Gas
10.7 ± 0.3 %
10.5 ± 0.5 %
LP Gas
300ppm
Bosch Water Heating
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