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Troubleshooting; Introduction; Burner Does Not Ignite When A Hot Water Faucet Is Opened; Water Is Too Hot - Bosch Greentherm 9800 SE 160/199 Manual

Indoor residential and comme rcial tankless water heaters
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48 | Troubleshooting

▶ Reconnect the electrical supply to the unit, open the water
shutoff valves, and return the unit to service.
Fig. 46
[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.


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 10).
Burner does not ignite when a hot water
faucet is opened
It is recommended to use "P4 Information" page 40, 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). Confirm power
to the heater.
6 720 816 815 (2016/10)
2. Verify the fuse in the control board is good. To access the
fuse, the control board must be removed. See chapter 5.2,
page 37.
3. Make sure cold water inlet connection is plumbed to the
right side of the heater when facing unit. See Fig.22, page
4. A minimum of 0.45 gallons per minute (1.5 l/m) for
199000 BTU and 0.55 gallons per minute (2.0 l/m) for
160000 BTU 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. In
unusual circumstances with high inlet water temperatures
and low set point temperatures, the heater may increase
the activation rate above 0.55 gpm to avoid overheating at
low flows. Gradually increase water flow (hot water
demand) through the heater to determine if the heater
activates with higher flow.
5. Clean the inlet water filter screen per chapter 4.10, page
6. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris.
7. 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 for water flow at each tap. There should be no water
flowing. Any continuous flow of water, small or large,
indicates a crossover is present and must be corrected.
Consult a professional plumber for help in correcting a
crossover. Failing single lever faucet mixing valves are
common causes of plumbing crossovers.
8. With the water heater's power supply cord unplugged,
remove the unit's front cover (See fig. 3, page 10). Check
all wire connections between the water valve, control unit
and electrode set. See chapter 51, page 57.

Water is too hot

1. Selected temperature on the unit is too high. To lower
output temperature, see chapter 6.4, page 38.
2. Clean inlet filter screen as instructed in chapter 7.1, page
46 to increase flow through the heater.
3. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris. It may be necessary to upgrade to higher
flow rate shower heads if allowed by local code.
Greentherm 9800 SE 160/199 | SEC 199



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