Water Is Too Hot; Water Is Not Hot Enough; Low Water Flow/Pressure; Hot Water Temperature Fluctuates At Tap - Bosch 520PN Applications Manual

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 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 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 power button pressed switch turned to OFF and the power
supply cord unplugged, remove the unit's front cover (See fig. 3, page
8). Check wire connections between the water valve, control unit and
electrode set. See chapter13.2, page 53 for location of these parts.
9. Water heater in solar mode. If inlet water temperatures exceed the
water heater's set temperature, the burners will not ignite and the
solar mode indicator will show on the display. See fig. 53, page 33.
8.3

Water is too hot

1. Selected temperature on the unit is too high. To lower output
temperature, see chapter6.4, page 33.
2. Clean inlet filter screen per chapter7.1, page 35 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.
4. Confirm the heater's gas type coincides with the type of gas being
supplied. See fig. 2, page 8 for location of rating plate.
5. Avoid restrictive outlets. Clean all shower heads and faucet aerators.
It may be necessary to upgrade to higher flow rate shower heads if
allowable by local code.
6. In areas where the water has a high mineral content, periodic
descaling may necessary. See chapter7.3, page 36 for directions.
8.4

Water is not hot enough

1. Selected temperature on the unit is too low. To raise output
temperature, see chapter6.4, page 33.
2. Clean inlet filter screen. See chapter7.1, page 35 to increase flow
through the heater.
3. Inspect the water path for obstructions. Make sure all showerheads,
faucet aerators and whole house filters are clear of debris.
4. Confirm the heater's gas type coincides with the type of gas being
supplied. See fig. 2, page 8 for location of rating plate.
5. Check inlet gas particle screen for blockage at gas inlet connection on
bottom of unit.
6. Verify gas pressure is in accordance with specifications in
chapter4.14, page 31. A gas pressure reading is needed to proceed
further. Contact your original installer or a local certified gas
technician to obtain this reading.
7. 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.
C 1210 ES/ESC
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
chapter4.14, page 31. 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.
3. If 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 inlet filter screen per chapter 7.1, page 35.
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. Hot water is very hot out of the water heater, requiring mixing in cold
water in order to attain a usable hot water temperature. The addition
of too much cold will overpower hot water flow from the tankless
water heater.
If this slows the flow through the tankless water heater below its
activation point, it will shut off the burners. The end result is nothing
but cold water coming out of the outlet. Consult www.bosch-
climate.us for a detailed service bulletin on overcoming temperature
fluctuations.
2. Unbalanced pressure in water lines. Any restriction in the water
heater, such as a clogged inlet 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 fell below the minimum flow rate
required for activation. Verify inlet filter screen is clean and clear of
debris. See chapter7.1, page 35 for inlet filter cleaning instructions.
3. Heater deactivated by temperature balancing valves. If the outlet
water temperature is set too high, the heater can produce
temperatures that are too hot. A temperature balance shower valve
will automatically mix in cold water to reduce the hot water
temperature. In the event of any temperature instability at a fixture
using a temperature balancing valve, refer to the valve manufacturer
for instructions on internal adjustment setting. An adjustment should
be made to minimize the amount of cold water the valve is adding.
Additionally, the temperature setting on the heater can be lowered to
prevent the temperature balance valve from mixing in too much cold.
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 40
- 60 psi (2.75 - 4.15 bar). Consult your installer or local plumber for
effective ways to maintain constant water pressure to the appliance
when on a well system.
Troubleshooting | 41
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