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Troubleshooting; Introduction; Burner Does Not Ignite When A Hot Water; Faucet Is Opened - Bosch Greentherm T9800 SEC 199 Installation And Operating Instructions Manual

Indoor residential and commercial tankless water heaters
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52 | Troubleshooting

8
Troubleshooting
CAUTION:
▶ If you are unable to perform the tasks
listed below, or need additional
assistance please contact a service
provider or contractor.
8.1

Introduction

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).
8.2

Burner does not ignite when a hot water

faucet is opened

It is recommended to use "P4 Information" page 43, 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.
2. Verify if the fuse in the control board is good. To access the
fuse, the control board must be removed. See chapter 5.2,
page 40.
3. Make sure cold water inlet connection is plumbed to the
right side of the heater when facing unit. See Fig.28, page
34.
4. 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.
5. Clean the inlet water filter screen per chapter 4.10, page
34.
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
6 720 816 815 (2018/08)
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/water flow
sensor, control unit and electrode set. See chapter 61,
page 65.
8.3

Water is too hot

1. Selected temperature on the unit is too high. To lower
output temperature, see chapter 6.4, page 41.
2. Confirm the heater's gas type coincides with the type of gas
being supplied. See fig. 2, page 10 for location of rating
plate.
8.4

Water is not hot enough

1. Selected temperature on the unit is too low. To raise output
temperature, see chapter 6.4, page 41.
2. Confirm the heater's gas type coincides with the type of gas
being supplied. See fig. 2, page 10 for location of rating
plate.
3. Verify gas pressure is in accordance with specifications in
chapter 4.13, page 39. A gas pressure reading is needed to
proceed further. Contact your original installer or a local
certified gas technician to obtain this reading.
4. Check inlet gas particle screen/filter for blockage at inlet
gas valve. Need to remove gas valve from the appliance.
5. Cold water is mixing into the hot water lines (plumbing
crossover). A plumbing crossover can unintentionally mix
cold water with the hot water leaving the heater. The end
result is a cooler water temperature than desired. 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 heater. Wait 10 minutes and check all taps for water
flow. There should be no water flowing. Any continuous
flow of water, small or large, indicates a crossover 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.
8.5

Low water flow/pressure

1. Too many hot water applications are being used
simultaneously or too much flow is demanded. The water
heater will effectively support two 2.0-2.5 GPM shower
heads simultaneously or multiple sink applications. Greater
draws will result in a water pressure drop and reduced flow
at taps.
Greentherm T9800 SE 160/199 | SEC 199

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