Troubleshooting; Introduction; No Spark At Pilot With Water Flow; Spark Appears When Hot Water Is Turned On, But Pilot And Burners Will Not Ignite - Bosch 520-HN -L Manual

26 | Troubleshooting

Fig. 24
7 Troubleshooting
7.1

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.bosch-
climate.us for more detailed troubleshooting bulletins. For
best results, perform each step before proceeding to the next.
The suggested solutions may require that the cover be taken
off. (See chapter 3.5).
7.2

No spark at pilot with water flow

Refer to service bulletin CT-09
1. Ensure that the On/Off button on control box is pushed to
the "On" position .
2. Ensure that cold water supply is attached to rear of water
valve and hot water outlet is on the left.
3. Measure voltage at hydrogenerator. Disconnect the wire
connector at hydrogenerator and measure voltage on
hydrogenerator side of connector.
– If the wires from the hydrogenerator are black and
red, the voltage should be at least 1.3VDC.
– If the wires from the hydrogenerator are blue and
brown, the voltage should be at least 2.8VAC.
6 720 644 942 (2014/11)
If the voltage is inadequate, refer to bulletin CT-29 to
clean the hydrogenerator.
4. Check for crossover:
– Turn off cold water supply to heater only. If no shut off
valve is present, install before continuing.
– Turn on each hot water fixture to hot only.
– Wait 5 minutes.
– If any water is flowing, even a trickle, there is a
crossover or the scald protection in a shower valve is
adjusted incorrectly. Consult plumber or faucet valve
manufacturer for repair or adjustment.
5. Rotate flow control (right knob) to full clockwise position
for the lowest activation rate of about 6 gallon per minute.
As the knob is turned counter-clockwise, the activation rate
will rise to about 1.1 gallons per minute.
6. Check for obstructions to water flow. Clean inlet filter
screen in water valve, whole house filters, showerheads
and faucet aerators. Obstructions such as dirt, debris or
mineral deposits will decrease the water flow through the
heater below the activation rate.
7. Check for tight and clean wire connections in heater:
– wire from ignition unit to spark electrode
– wires to flue gas sensor on draft diverter
– wires to overheat sensor on outlet pipe
– wires to overheat sensor on heat exchanger
– wires to microswitch
– ground wire connection between ignition unit and
fixing screw
8. If a powervent and spill switch are installed, check the reset
button on the spill switch (installed on the draft diverter).
Consult powervent manual for more details.
– If the button clicks when pushed, the switch was
tripped. Check venting for restrictions and exhaust
hood damper for correct operation.
9. Check microswitch on bottom of gas valve. Disconnect
wire connector at microswitch and jump connector on
wiring cable. Run water through heater.
– If heater sparks, check continuity through microswitch
connector with water flow. If circuit does not close one
of the following may be the cause; microswitch is
faulty, water valve needs maintenance or flow is
inadequate.
10. If heater still does not spark, contact Bosch technical
support.
7.3 Spark appears when hot water is turned on,
but pilot and burners will not ignite
1. Refer to service bulletin CT-10
If there is a spark from the spark electrode with water flow,
but the pilot does not ignite:
520 HN