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Water Is Not Hot Enough; Low Water Flow/Pressure; Hot Water Temperature Fluctuates At Tap; Noisy Burner/Heater During Operation - Bosch Greentherm 9800 SE 160/199 Manual

Indoor residential and comme rcial tankless water heaters
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4. Confirm the heater's gas type coincides with the type of gas
being supplied. See fig. 2, page 10 for location of rating
plate.
5. In areas where the water has a high mineral content,
periodic descaling may necessary. See chapter 7.3, page
47 for directions.
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 38.
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 36. 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.
2. Ensure that gas pressure is in accordance with
specifications in chapter4.13, page 36. A gas pressure
reading is needed to proceed further. Contact your original
installer or a local certified gas technician to obtain this
reading. If gas pressure is inadequate, the water heater will
close its motorized water valve, reducing the hot water flow
rate in an attempt to reach the selected output
temperature.
Greentherm 9800 SE 160/199 | SEC 199
3. If the selected temperature on the unit is set too high for the
demanded flow rate, the water heater will close its
motorized water valve, reducing the hot water flow rate in
an attempt to reach the selected output temperature.
Lowering the selected temperature will allow the motorized
water valve to open up for increased water flow rate.
4. Clean the inlet water filter screen as instructed in chapter
7.1, page 46.
5. Inspect the water path for obstructions. Make sure all
shower heads, faucet aerators and whole house filters are
clear of debris.
8.6

Hot water temperature fluctuates at tap

1. If the water heater set point temperature is high, mixing at
the faucet could deactivate the water heater. The addition
of too much cold will overpower hot water flow from the
tankless water heater reducing its flow below the activation
point.
If this slows the flow through the tankless water heater
below its activation point, it will shut off the burner.
2. Unbalanced pressure in water lines. Any restriction in the
water heater, such as a clogged inlet water filter screen,
can result in unequal pressures between the cold and hot
water lines. In such cases, when mixing in the higher
pressure cold water at the tap, the lower pressure hot
water can be overpowered. This will shut down the burners
because the hot water flow rate falls below the minimum
flow rate required for activation. Verify that the inlet water
filter screen is clean and clear of debris. See chapter7.1,
page 46 for inlet water filter cleaning instructions.
3. The water heater may be deactivated by temperature
balancing shower valves. If the water heater's set point
temperature is set too high, the temperature balance
shower valve will automatically mix in cold water to reduce
the hot water temperature. An adjustment should be made
to minimize the amount of cold water the valve is adding.
Additionally, the temperature setting on the water heater
can be lowered to reduce the amount of cold water that the
temperature balance valve mixes in.
4. Inlet water pressure is erratic due to fluctuating supply
water pressure. For installation on a private well system
with the use of a pressure tank, the lowest pressure range
setting recommended is 30 - 45 psi (2.06 - 3.1 bar).
Consult your installer or local plumber for effective ways to
maintain constant water pressure to the appliance when on
a well system.
8.7

Noisy burner/heater during operation

1. Make sure the cover is securely fastened. Ensure the
exhaust vent adaptor is properly sealed with the supplied
gasket. Leaky seals create improper combustion emissions
and noise.
Troubleshooting | 49
6 720 816 815 (2016/10)

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