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Troubleshooting; Introduction; Burner Does Not Ignite When A Hot Water Faucet Is Opened - Bosch Greentherm T9800 SEO199 Installation And Operating Instructions Manual

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▶ Run the solution through the heater until the solution
returning to the descaling reservoir comes out clear.
(Changing to a fresh solution may be necessary during this
▶ Disconnect all lines and drain all solution from heat
exchanger. Properly discard the solution.
▶ Close the inlet drain connection.
▶ Position a container below the hot water outlet and connect
the cold water supply. Open the cold water supply shutoff
valve and flush the heat exchanger with clean water.
▶ Close the cold water shutoff valve and reconnect hot water
supply to the water heater.
▶ Close the outlet drain connection.
▶ Reconnect the electrical supply to the unit, open the water
shutoff valves, and return the unit to service.
Fig. 37
[1] Pump
[2] Water filter
If you are unable to perform the tasks listed below, or need
additional assistance,
▶ Please contact a service provider or contractor.
In some areas local code may require that the tasks described
in this section must be performed by a certified contractor.
▶ Please check your local codes to ensure compliance.


Many of the questions customers ask regarding operation of
this unit can be answered by following the troubleshooting
steps as outlined below. For best results, perform each step
before proceeding to the next. The suggested solutions may
require that the cover be taken off. (See fig. 3, page 3).
Burner does not ignite when a hot water
faucet is opened
It is recommended to use "P4 Information" page 29, chapter
6.5.1 as a tool for problem solving.
1. If the display is blank, verify power at the outlet. (120VAC/
60Hz properly grounded circuit required). Verify the heater
power supply. Check all wire connections including
plugged connectors.
2. With the water heater's power supply OFF and the power
supply cord unplugged, remove the unit's front cover (See
fig. 3, page 11). Check wire connections between the
water valve, control unit and electrode set. See fig. 46,
page 49.
3. Verify the fuses in the control board are good. To access the
fuses, the control board must be removed. See
chapter 5.2, page 26.
4. Make sure cold water inlet connection is plumbed to the
right side of the heater when facing unit. See Fig. 13,
page 19.
5. A minimum of 0.45 gallons per minute (1.7 l/m) of hot
water demand is required to activate the heater. Confirm at
least 0.4 gpm flow by timing how long it takes to fill a
container. A quart container should fill in 20 seconds or
less, from the hot water tap only. Gradually increase water
flow (hot water demand) through the heater to determine if
the heater activates with higher flow.
6. Clean the inlet water filter screen per chapter 4.9, page 19.
7. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris.
8. Check for a plumbing crossover. A crossover in the hot and
cold plumbing pipes creates back pressure on the water
flowing through the heater. Therefore, a higher flow rate
than normal is needed to force the heater to activate. To
check for a plumbing crossover, shut off the cold water
supply to the water heater. Then open all of the hot water
taps served by the water heater. Wait 10 minutes and check
Greentherm T9800 SEO 160/199 | SECO 199 – 6 720 817 281 (2018/12)



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