Bosch AQ250SX Service Bulletin Booklet Download Page 1

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Service Bulletin Booklet

For Bosch model water heaters
GWH 635 ES, GWH 635 ESO,
GWH 2400 E, GWH 2400 EO,
AQ250SX, AQ250SXO

Summary of Contents for AQ250SX

Page 1: ...Service Bulletin Booklet For Bosch model water heaters GWH 635 ES GWH 635 ESO GWH 2400 E GWH 2400 EO AQ250SX AQ250SXO ...

Page 2: ...ng temperature sensors 9 TWH G2 06 Winterizing and freeze prevention 11 TWH G2 07 Control board diagnostics 13 TWH G2 11 Unlocking stuck water valve 15 TWH G2 12 Measuring and adjusting CO2 17 TWH G2 13 Descaling 19 TWH G2 22 Replacing heat exchanger 21 TWH G2 23 Replacing and cleaning electrodes 23 TWH G2 24 Replacing control unit 25 TWH G2 25 Gas conversion 27 TWH G2 26 Replacing water valve 29 ...

Page 3: ...minutes and check all taps The water flow should come to a complete stop at every tap 3 Any water running is a sign of a plumbing crossover Consult a local plumber or service person for help This condition must be corrected before the heater can operate properly Confirm water pressure Water pressure must stay above 30psi during heater operation For installation on a private well system with the us...

Page 4: ...Bosch Water Heating BBT North America Corporation Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com Lower temperature Use the controls on the front on the heater to lower the output temperature Most people use hot water in the range of 100 110F ...

Page 5: ... driver do not remove and connect manometer tube on test tap if manometer fitting goes inside the tap remove screw Static Pressure Test 1 Turn gas supply back on 2 Operate all other gas appliances on same gas piping system at maximum output 3 Gas pressures lower than 5 W C for Natural Gas or 11 W C for Liquid Propane will result in insufficient degree rise to the hot water being used and must be c...

Page 6: ...eld VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com Common causes of low gas pressure Appliance gas connector is not at least Gas line was not sized large enough Most often found in retrofit applications The gas filter on the bottom of the unit is clogged with pipe dope or other debris Gas meter or regulator is not set to deliver enough gas or is defective Have gas o...

Page 7: ...er to the off position 2 When turning power switch to the on position note the first two letters that appear on the display either AF or SU 3 Make note of the two letters that appeared Manual version 1 In the lower left hand corner of the remote control manual there are a series of numbers Both manuals have the numbers 6 720 606 990 followed by numbers in parantheses Manual version 6 720 606 990 0...

Page 8: ...BBT North America Corporation Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com Service bulletin 8 TWH G2 04 2400E 2400EO 250SX 250SXO 635ES 635ESO TWH G2 04 2400E 2400EO 250SX 250SXO 635ES 635ESO ...

Page 9: ...ould be located on the horizontal pipe The cold water temperature sensor is connected with two blue wires and should be clipped to the diagonal pipe See below Hot sensor Cold sensor Hot sensor Cold sensor Temperature sensor location 3 If the either sensor is not in it s respective location move to the proper location immediately Ensure that the sensor is firmly clipped and making good contact with...

Page 10: ... water fixture such as a sink and allow water to run steadily through the water heater for 5 minutes Using a thermo meter measure the temperature of the water flowing out of this tap Continue running water and go back to the water heater 5 Using a multi meter set on kilo ohms kΩ measure the resistance between the two connections of each sensor and record readings 6 Refer to the table below for res...

Page 11: ...ation 1 Turn on off switch on the water heater to the off O position and unplug power supply cord The display should be blank 2 Shut off gas supply to heater 3 Shut off the water supply to the water heater using installer supplied shutoff valve 4 Open hot water taps to drain and relieve pressure from the plumbing system If water continues to flow after 5 minutes a plumbing crossover is present and...

Page 12: ...ulletin Data subject to change without notice Printed in the USA 1 2007 Bosch Water Heating BBT North America Corporation Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com ...

Page 13: ...utton on the control panel until the display reads P4 You are now in the diagnostic mode of the control board 5 When the display reads P4 press the P button once again and the display should read E 6 Use the and button on the control board to cycle through different diagnostic modes available NOTE Each diagnostic mode that appears on the LCD display will have a number on the left and a letter on t...

Page 14: ...election 1F Most recent error failure 2F 2nd most recent error 3F 3rd most recent error 4F 4th most recent error 5F 5th most recent error 6F 6th most recent error 7F 7th most recent error 8F 8th most recent error 9F 9th most recent error 10F 10th most recent error Software version 3005 diagnostic codes E Entry Exit into sub modes 0d Set point temperature 1d Inlet water temperature 2d Outlet water ...

Page 15: ...ming from the control board and starting at one side you will see a black wire then a red wire and then a green wire on older models this wire was brown Using a very small screwdriver push down on the silver tab to release and disconnect the green wire or brown for older models from the connector 5 Leaving the green wire or brown wire for older models discon nected plug the 2 connectors back toget...

Page 16: ...BT North America Corporation Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com Service bulletin 16 TWH G2 11 2400E 2400EO 250SX 250SXO 635ES 635ESO TWH G2 04 2400E 2400EO 250SX 250SXO 635ES 635ESO ...

Page 17: ...ing port The tip of the probe should be in the center of the flue pipe approx 1 5 inserted 4 While holding the Program M button move the ON OFF switch to ON I position As soon as 188 flashes on the display release the program button The display should now read P2 Program mode Measuring CO2 1 Open hot water taps to achieve a flow rate of at least 4 gallons per minute 1 tub and 2 sinks should be suf...

Page 18: ...ll be revealed Adjusting P2 CO2 level 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 Final readings 1 Verify both P1 and P2 are within the ranges specified in the table below Continue adjusting the P1 and P2 levels as necess sary until C...

Page 19: ...ne C from the descaling reservoir connect to the inlet side of circulating pump Verify that there is a filter on the end of the line in the descaling reservoir 8 Make sure all connections are hand tight 9 Fill tank with descaling solution so both lines inside are submer sed We recommend straight white vinegar If using a commer cial descalant refer to manufacturer s instructions on dilution with wa...

Page 20: ...ulletin Data subject to change without notice Printed in the USA 03 2007 Bosch Water Heating BBT North America Corporation Bosch Group Bosch Water Heating 340 Mad River Park Waitsfield VT 05673 Telephone 800 642 3111 Fax 802 496 6924 techsupport boschhotwater com ...

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