Water Is Too Hot; Water Is Not Hot Enough; Burners Ignite Without Hot Water Flow; 7.10 Low Hot Water Pressure - Bosch 520-HN -L Manual

(directly after the pressure tank on well systems) may be an
effective way to maintain constant water pressure to the water
heater.
5. If the inlet water temperature is not steady then the hot
water temperature from the water heater will fluctuate. The
330 PN modulates its burners when the flow rate is changed; it
does not have a thermostat and will not adjust to changes in
inlet water temperature.
6. If the inlet water temperature to the water heater is above
70°F, the heater may produce outlet temperatures that are too
hot for most users. A temperature balance shower valve can
automatically mix in cold water to reduce such hot water
temperature. This can slow the flow within the tankless water
heater, decreasing it below activation point, which shuts off the
burners. In the event of any temperature instability with the use
of a temperature balance shower valve, refer to shower valve
manufacturer's instructions for internal adjustment setting. An
adjustment should be made to minimize the amount of cold
water the valve is adding.
7. The gas pressure also needs to be stable and adequate.
Ensure gas pressure is in accordance with manufacturer's
specifications (see chapter 4.8). A gas pressure reading is
needed to proceed further. Contact your original installer or a
local certified gas technician to obtain this reading.
7.7

Water is too hot

1. Verify that gas type indicated in the rating sticker located on
the cover's right hand side coincides with the gas type you are
using. NG is a natural gas unit and LP is for liquid propane (See
chapter 2.2).
2. Adjust the power adjustment knob clockwise for cooler
temperatures. See section 4.4.
3. Inlet water is preheated. This model does not have a
thermostat and will not modulate flame height in order to
prevent overheating. It is designed for cold water supply only.
Supply the heater with cold water to the inlet.
4. Increase flow rate. Restrictions in the water path can slow
the flow of water through the heater, resulting in very hot outlet
temperatures. Restrictive showerheads and faucet aerators
should be cleaned or upgraded with less restrictive ones. In
addition, the inlet filter on the water heater should be cleaned
and inspected. See chapter 5.2.
5. If the water has a high mineral content, the heat exchanger
may be scaled internally. This restricts the water path, causing
the water to boil and produce extremely hot temperatures. To
descale the heat exchanger, section 5.6.
7.8

Water is not hot enough

1. Verify that gas type indicated in the rating sticker located on
the cover's right hand side coincides with the gas type you are
520 HN
using. NG is a natural gas unit and LP is for liquid propane (see
chapter 2.2).
2. Flow at one particular tap is too great or too many fixtures are
running at one time. Lower flow to stay within heater's
specifications.
3. Ensure that the gas control knob is all the way counter-
clockwise for highest temperatures. In addition, the flow
control knob maybe set too high. Raise the setting by turning
the knob clockwise for higher temperatures.
4. Close installer supplied cold water shut off valve (if none
installed, install before proceeding). Open every hot water tap
supplied by the heater. Wait 5 minutes and check all taps. Any
water running, even a trickle, is a sign of a plumbing crossover.
Consult local plumber or service person for help correcting a
plumbing crossover.
5.Inspect the water path outside the heater for obstructions.
Make sure all showerheads, faucet aerators and whole house
filters are clear of debris. Also, the water heater's inlet filter
should be inspected and cleaned. See chapter 5.2.
6. The water valve assembly, which allows gas flow to the
burners, requires periodic maintenance (every 2-5 years
depending on water quality and use). See section 5.2.
7. Gas pressure is too low. Ensure that gas pressure meets
specifications meets chapter 3.9. A gas pressure reading is
needed to proceed further. Contact your original installer or a
local gas technician to obtain this reading.
7.9

Burners ignite without hot water flow

1. The water valve may be dirty and sticking, prohibiting it from
fully closing the gas valve. This part needs to be periodically
serviced (every 2-5 years depending on water quality and use)
(see chapter 6.2).

7.10 Low hot water pressure

1. Confirm adequate flow rate through the unit. With cold
supply shut off to the unit, disconnect hot outlet side to the
unit. Place a gallon jug under hot water outlet to catch water.
Open cold water supply and measure flow rate out of the unit.
With temperature adjustment knob set all the way clockwise,
the flow rate should be close to 2GPM (filling the jug in 30
seconds or less). If the flow rate is not adequate, inspect and
clean inlet filter screen. See chapter 5.2.
2. Confirm the incoming water pressure to the unit is above the
required 30psi.
3.Inspect the water path outside the heater for obstructions.
Make sure all showerheads, faucet aerators and whole house
filters are clear of debris.
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