Bosch 520-HN-N Specifications download pdf (Page 20)

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Troubleshooting

• 5. Confirm wire connection to the pilot electro valve

is secure. See Components Diagram for location.

Inspect terminals for corrosion. To clean terminals,

remove the spade connectors and clean with a pencil

eraser

• 6. Open a hot water faucet. While sparking, hold a

flame from a lit match or lighter in the pilot area. If the

pilot successfully lights, the pilot orifice may be dirty

or clogged. See chapter 5.3 on how to clean the pilot

• 7. Verify adequate voltage at the spade connection of

the pilot electro valve. When sparking, voltage

should read 1.6VAC. If voltage is proper, pilot electro

valve is defective. If voltage is not proper, electronic

control box is defective.

Visit www.boschhotwater.com

to purchase

replacement part, or call Bosch Water Heating at

800-642-3111 for replacement part if still under

warranty.

6.4 Pilot light, but burners will not

come on.

• 1. Verify gas type indicated in the rating sticker

located on the cover's right hand side, coincides with

the gas type you are using. NG is a natural gas unit

and LP is for liquid propane (See chapter 2.2).

• 2. Pilot flame should be blue in color and completely

engulfing the flame sensor. If not, the pilot orifice may

be dirty or clogged. See chapter 5.3 on how to clean

the pilot.

• 3. Flame sensor not recognizing pilot flame. Verify

wire connection clip on wire from the bottom of the

flame sensor is secure. If flame sensor is fully

engulfed by the pilot flame, it may be dirty. Clean

entire surface area of flame sensor with a pencil

eraser.

• 4. Inspect the water path for obstructions. Make sure

all outlets (i.e. showerheads, faucet aerators and

whole house filters) are clear of debris. Inspect and

clean the water heater's inlet filter screen. See

chapter 5.2.

• 5. Confirm wire connection to the burner electro

valve is secure (see components diagram for location

of burner electro valve). Inspect terminals for

corrosion. To clean terminals, remove the spade

connectors and clean with a pencil eraser.

• 6. The water valve assembly, which allows gas flow

to the burners, requires periodic maintenance (every

2-5 years depending on water quality and use). Visit

www.boschhotwater.com to purchase water valve

rebuild kit to service the water valve

• 7.Electric control box, burner electro valve or flame

sensor maybe damaged/defective. Verify adequate

voltage at the spade connection of the burner electro

valve (see components diagram for location of burner

electro valve). After the pilot lights, voltage should

read 1.6VAC on the burner electro valve. If voltage

is proper, the burner electro valve is defective. If

voltage is not proper, electronic control box or the

flame sensor is damaged/defective.

Visit www.boschhotwater.com to purchase

replacement part, or call Bosch Water Heating at

800-642-3111 for replacement part if still under

warranty.

Fig. 25 Electrical wiring diagram

2 Pilot electrode

3 Flame sensor

23 Electronic control box

25 Burner electro valve

27 Gas control valve

28 Pilot electro valve

31 Temperature limiter

32 Flue gas safety device

34 LED indicator main burner operation

50 Hydro-generator

51 On/Off switch

110 LED failure control box

111 Overheat limiter

6.5 Main burners go out during hot

water use

• 1. Hot water flow rate is dropping below required

activation flow rate. Turn temperature adjustment

knob all the way clockwise. Fully open a hot water

faucet and fill a quart container. If the container fills in

30 seconds or less, the flow rate (1/2 gallon per

minute) is sufficient to activate the water heater. If

flow rate is not sufficient, the water heater's inlet filter

should be inspected and cleaned. See chapter 5.2.

• 2. Close installer supplied cold water shut off valve (if

none installed, install before proceeding). Open all

hot water taps supplied by the heater. Wait 5

minutes and check all taps. Any water running is a

sign of a plumbing crossover. Consult local plumber

or service person for help correcting a plumbing

crossover.

• 3. The minimum water pressure for the home should

be 30psi or greater. For installation on a private well

system with use of a pressure tank, the lowest

pressure range setting recommended is 30-50 psi

(2.07-3.45 bar).

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Bosch 520-HN-N Specifications Page 20

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