Bosch Appliances 250SX LP, 250SX NG manual Maintenance and service, Troubleshooting

Maintenance and service

4Maintenance and service

Warning: Always turn off the electrical power supply, turn off the manual gas valve and turn off the manual water control valves whenever servicing.

The unit should be checked once a year by a gas technician. If repairs are needed, the repairs should be done by a gas technician

To remove front cover

BRemove plastic decals on front panel (Page 5, Fig. 4).

BLoosen the two Philips head screws located behind decals.

BLift front cover panel upward and remove.

Systems and parts that should be checked at least once a year

Reference diagrams on pages 29 and 30.

•Venting system

•Burners -see page 29 for observation window

•Manual operation of the pressure relief valve to insure correct operation

•Periodic cleaning of the water filter screen, see Fig. 24, chapter 2.13.

•Flushing the heat exchanger with a descaling solution if mineral build up is evident. Scale build up will shorten the life of the water heater, descale heat exchanger thoroughly and repeat annually depending on mineral content of ground water.

5Troubleshooting

Introduction

The 250 SX burner is activated by a water flow valve. Numerous water related problems can cause this water valve to malfunction such as: Insufficient water flow volume to activate the burners at its minimum flow requirement; Dirt in the water flow valve causing it to malfunction; Sediment build-up in faucet aerators, or shower heads; Uneven pressures between cold and hot (with single lever mix valves); and Plumbing crossovers. These water flow related problems can cause the heater to deliver less than its full output, or to fail to ignite or to shut down completely.

Problems stated below in upper case and in bold face should be investigated when there is a problem with the performance of the water heater but there is NO error code on the heater's LCD display or wireless remote control.

Any failures that result in a displayed error code are referenced on page 26. A Functional Scheme of the 250 SX is detailed on page 28. If there is a problem with the installation, venting or operation of the unit, the

heater will communicate the source by these error codes.

BURNERS DO NOT IGNITE WHEN HOT WATER IS TURNED ON

•Cold incoming water connection made to wrong side of heater

Make sure cold water inlet connection is plumbed to the right side of heater when facing unit

•Water flow rate at hot water tap is too low

A minimum of 0.8 gallon/minute (3 l/m) is required to activate the heater

•Cold water inlet filter screen is dirty

Remove water inlet filter screen and clean. The screen is located at the inlet connection to the water heater, disconnecting the main cold supply line at the heater is required. Check and clean faucet aerator screens too.

•Crossover in plumbing

The heater activates when there is sufficient water flow through its water valve, a minimum of 0.8 gallon/ minute (3 l/m) is required. If there is a crossover in the plumbing, the necessary hot water flow rate through the unit may not be reached, even though the flow at the hot water tap is sufficient. A plumbing crossover can be caused by a failed washer at a single lever faucet, incorrect plumbing or a faulty mixing valve in the piping. The crossover will create a back pressure on the water heater and prevent an adequate flow of water through it. To confirm there is no crossover in the plumbing, shut off the cold water supply feed to the water heater. Individually open each of the hot water taps. There should be no water flowing under a constant pressure. If there is a constant flow of water then the plumbing crossover must be corrected before the heater can operate properly.

WATER IS TOO HOT

•Temperature selection too high

Lower temperature adjustment on heater or wireless remote control accessory, see chapter 3.2.

WATER IS NOT HOT ENOUGH

•Temperature selection too low

Increase temperature adjustment on heater or wireless remote control accessory, see chapter 3.2

•Btu input is too low due to inadequate gas line sizing

See specifications in chapter 2.10 - 2.12. The 250 SX requires adequate gas pressure to reach desired temperatures, to compensate for inadequate gas supply or lack of gas pressure the 250 SX will effectively reach the selected output temperature by reducing the hot water flow rate. Its motorized water valve makes this adjustment

•Cold water is mixing with the hot water outlet (crossover)

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