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Burners Do Not Light With Water Flow; Hot Water Temperature Fluctuates At Tap - Bosch 330-PN-N Installation Manual

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26 | Troubleshooting
proper draft.
4. Confirm that the burners in the water heater go off
immediately when the hot water is turned off. If they remain on
or shut down slowly, then the overheat sensor (ECO) will
interrupt the pilot circuit and shut off all gas to the heater. The
water valve assembly, which actuates the burners, may be dirty
and require periodic maintenance (every 2 - 5 years depending
on water quality and use) (see chapter 6.2).
5. Check all connections of the pilot safety circuit. The pilot
safety circuit consists of a thermocouple, overheat sensor
(ECO), flue gas sensor and the electromagnet (See parts
diagram for locations). Clean sensor connections with light
sandpaper if corrosion is evident. The electromagnet
connection is 5mm nut from the thermocouple which screws
into a larger 17mm nut. Tighten both nuts snugly but do not
over tighten.
6. Verify pilot flame completely engulfs the thermocouple tip. If
pilot is too small, clean pilot orifice (see chapter 6.3).
7. If the water has a high mineral content, the heat exchanger
may be scaled internally. This restricts the water path, causing
the water to over heat which shuts all gas off to the heater.
Instructions for descaling the heat exchanger are available at
www.bosch-climate.us.
8. If steps 1 through 7 do not correct the problem, then confirm
that the gas pressure is adequate. Ensure gas pressure is in
accordance with manufacturer's specifications (see
chapter 4.9). A gas pressure reading is needed to proceed
further. Contact your original installer or a licensed gas
technician to obtain this reading.
7.5

Burners do not light with water flow

1. Verify the pilot is lit.
2. Verify the gas control slide button is in middle position.
3. Verify the cold water supply is connected to the right side of
the heater.
4. Close installer supplied cold water shut off valve (if none
installed, install before proceeding). Open all hot water taps
supplied by the heater. Wait 5 minutes and check all taps. Any
water running is a sign of a plumbing crossover. Consult a local
plumber or service person for help in correcting a plumbing
crossover.
5. Verify flow through the water heater is sufficient. Turn
temperature adjustment knob all the way clockwise. Fully open
a hot water faucet and fill a quart container. If the container fills
in 30 seconds or less, the flow rate (1/2 gallon per minute) is
sufficient to activate the heater.
6. Inspect the water path outside of the heater for
obstructions. Make sure all outlets (i.e. showerheads, faucet
aerators and whole house filters) are clear of debris. Also, the
6 720 644 951 (2014/11)
water heater's inlet filter screen should be inspected and
cleaned (see chapter 6.2).
7. The water valve assembly, which actuates the burners,
requires periodic maintenance (every 2 - 5 years depending on
water quality and use) (see chapter 6.2).
7.6

Hot water temperature fluctuates at tap

1. Close off installer supplied cold water shut off valve (if none
installed, install before proceeding). Open all hot water taps
supplied by the heater. Wait 5 minutes and check all taps.
Water running is a sign of a plumbing cross-over. Consult a local
plumber or service person for help in correcting a plumbing
crossover.
2. Check for a clogged inlet water filter screen (see
chapter 6.2).
3. Hot water is very hot out of the tap, requiring a lot of cold
water to be added with it in order to attain a usable hot water
temperature. The addition of too much cold will overpower and
slow the flow within the tankless water heater, decreasing it
below activation point, which shuts off the burners. The end
result is nothing but cold water coming out of the outlet.
Reduce the need for cold water mix by setting the gas slide
control button towards the single flame position for lower hot
water temperatures. If the problem persists, go to www.bosch-
climate.us for a more detailed service bulletin on this problem.
4. The 330 PN is designed to modulate gas flow to the burners
when water flow varies. If the water pressure in the home is
erratic and the water flow is not consistent while a tap is
opened, then the temperature of hot water will fluctuate. The
minimum water pressure for the home should be 30psi or
greater. For installation on a private well system with the use of
a pressure tank, the lowest pressure range setting
recommended is 30-50 psi (2.07-3.45 bar). The use of a
pressure reducing/regulating valve before the water heater
(directly after pressure tank on well systems) is an effective
way to maintain constant water pressure to the water heater.
Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/
regulating valves or equivalent are suggested.
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
330 PN

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