Bosch GWH 425 PN Specifications download pdf (Page 18)

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Troubleshooting

6 Troubleshooting

6.1 Introduction

Many of the questions customers ask regarding

operation of this unit can be answered by following the

troubleshooting steps as outlined below. Visit our web

site at www.boschpro.com for more detailed

troubleshooting. For best results, perform each step

before proceeding to the next. The suggested solutions

may require that the cover be taken off. (See chapter

3.4).

6.2 Pilot will not light

If the unit sparks, skip to step 7.

B 1. Check the On/Off switch to be sure it is in the ON

(I) position. See fig. 11.

B 2.Turn temperature adjustment knob all the way

clockwise. Turn hot water faucet to full on position

and fill a quart container. If the container fills in 30

seconds or less your flow rate (1/2 gallon per minute)

is sufficient to activate the heater. If the knob is full

counter clockwise, the container will need to fill in 14

seconds (1.1 gallons per minute) to activate the

heater. Check for restrictions in the water line such

as clogged aerators or a clogged inlet water filter

screen if flow rate is not sufficient.

B 3. Clean water inlet filter screen. See chapter 5.2.

B 4. Shut off installer supplied cold water supply valve

(if none installed, install before proceeding). Open all

hot water taps supplied by the 425 HNO. Wait 5

minutes and check all taps. Water running is a sign

of a plumbing cross-over. Consult a local plumber or

service person for help in correcting plumbing cross-

over.

B 5. Verify the cold water supply is connected to the

right side of the heater.

B 6. Check that the connections to the ECO are secure

and tighten if necessary.

B 7. Disconnect wire connector between hydro-

generator and the electronic control box. Turn hot

water tap to full on position and measure voltage

between two pins on hydro-generator side of the

connector. If voltage is not 1.4-1.6 vdc, clean the

hydro-generator. Procedure is available on our

website at www.boschpro.com. Replace hydro-

generator if cleaning does not produce the required

voltage.

B 8. If the unit was just installed or the gas lines have

been worked on, there may be air in the gas line. To

bleed air out of the gas line, turn hot water tap on and

leave on while unit is sparking. Once unit stops

sparking, turn hot water tap off and then turn back on.

Repeat this procedure until pilot lights and the heater

fires. It is not unusual to have to cycle the heater 20-

30 times before the heater fires the first time.

B 9. Check to make sure the manual gas shut off valve

is in the open position. Have licensed gas technician

or service person check the presence of gas at the

gas pressure measuring tap on the left side of the

gas control valve. If gas is not present, the regulator

may be locked up and need replacing. See chapter

3.5 for required gas pressures.

B 10. Clean or replace the pilot orifice. See chapter 5.2

for instructions.

B 11. Service the water valve. See chapter 5.1 for

intervals and instructions.

B 12. Measure voltage on orange wire connected to

the pilot electro-valve. While the unit is sparking the

required voltage is 1.4-1.6 vdc. If this voltage is

present, the pilot electro-valve may need to be

replaced. If the voltage is not present, check all wire

connections to and from the electronic control box

are connected and clean. Replace electronic control

box if unit still does not light.

6.3 Pilot lights but the burners will not

come on

B 1. Pilot flame should be blue in color and hitting the

flame sensor rod. See chapter 5.2 instructions. If it

is, lightly clean flame sensor rod with emory cloth.

B 2. Service water valve See chapter 5.1 for intervals

and instructions.

B 3. Measure voltage on green wire connected to the

burner electro-valve. While the pilot is lit the required

voltage is 1.4-1.6 vdc. If this voltage is present, the

burner electro-valve may need to be replaced. If the

voltage is not present, check all wire connections to

and from the electronic control box are connected

and clean. Replace electronic control box if unit still

does not light.

6.4 Hot water temp fluctuates from hot

to cold

B 1. Shut off installer supplied cold water supply valve

(if none installed, install before proceeding). Open all

hot water taps supplied by the 425 HNO. Wait 5

minutes and check all taps. Water running is a sign

of a plumbing cross-over. Consult a local plumber or

service person for help in correcting plumbing cross-

over.

B 2. Check for restrictions in the water line such as

clogged aerators, clogged shower head or a clogged

inlet water filter screen.

B 3. If hot water is so hot that a large amount of cold

water must be introduced to lower temperature to

comfortable level, lower output temperature. See

chapter 4.4 for instructions.

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Bosch GWH 425 PN Specifications Page 18

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