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Pilot Lights But Burners Will Not Come On; Water Is Too Hot; Water Is Not Hot Enough; Main Burners Go Out During Hot Water Use - Bosch WR 400-7.K Series Installation & Operation Manual

Bosch wr 400-7.k.. instantaneous gas water heater
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PILOT LIGHTS BUT BURNERS
WILL NOT COME ON
1. Confirm water valve assembly is working properly.
2. Confirm the flame sensor is in its proper position.
3. Confirm the burner electrovalve switch is functioning
properly. Contact your service person or call:
Canada 1-800-663-8405, U.S.A. 1.800-824-7337.
4. The electrical Control Box (Fig. 16) may need to be
replaced. Contact your service person or call:
Canada 1-800-663-8405, U.S.A. 1.800-824-7337.
Fig. 14 - Electrical wiring diagram
1
burner electrovalve
2
gas control valve
3
pilot electrovalve
4
flame sensor
5
pilot electrode
6
overheat sensor
7
temperature limiter
MAIN BURNERS GO OUT DURING HOT
WATER USE
1. Flow rate diminished below activation rate
2. Unbalanced pressure in the water lines
The added restriction caused by the Bosch in the hot water
system can result in uneven pressures between the cold and
the hot. In such cases when mixing cold water at the tap, the
lower hot water pressure may be overpowered by a much
higher cold water pressure, which may cause the Bosch
burners to shut down. Make sure faucet aerators and
showerheads are free of minerals and dirt. Do not add any
flow restrictor to the shower head.
3. ECO (overheat sensor) tripped due to overheating
Re-ignite the appliance 10 minutes later. Contact your serv-
ice person or call:
Canada 1-800-663-8405, U.S.A. 1.800-824-7337.
4. Flue Gas safety device tripped
Ventilate the room and re-ignite the appliance 10 minutes
later. Contact your service person or call:
Canada 1-800-663-8405, U.S.A. 1.800-824-7337.
6 720 606 560
8
electronic control box
9
Led failure indicator
10
Led indicator main
burner condition
11
on/off switch
12
power generator
13
flue gas safety device
5. Minimum inlet pressure on well is inadequate
Check the inlet water pressure. On a private well, raise the
minimum pressure setting to 40 psi for best performance.
Confirm that the pressure tank is not water logged.

WATER IS TOO HOT

1. Check for lime build-up. (See mineral scale p. 9)
2. Temperature Selection too high
Turn the temperature adjustment knob counter-clockwise (to
the left) to lower the maximum water temperature.
Note: This will increase the activation flow rate.
3. Inlet water temperature is too hot (as with preheated
water.)
Decrease gas pressure. If this is not practical install
tempering valve at inlet and mix with cold water.

WATER IS NOT HOT ENOUGH

1. Temperature selection too low.
Change the setting. Turn the temperature adjustment knob
clockwise (to the right).
Note: This will decrease the activation flow rate.
2. Water flow through the heater is higher than the
capacity of the Bosch to heat it.
This can be due to too high water inlet pressure (60 psi max.
for best results) or due to acid water erosion of venturi. Check
venturi (Part #30, Fig. 16).
3. Btu input is too low due to insufficient gas pressure. It
is extremely important for a tankless instantaneous water
heater to have the right size gas line to obtain the correct
gas pressure.
See specifications on page 8. Unlike storage tank water
heaters, the burners of a tankless water heater must be very
powerful to heat water instantaneously since they do this
only at the time hot water is actually being used. It is therefore
imperative that the gas pressure requirement be met exactly.
Insufficient gas pressure will directly affect the water
temperature at the time of usage. See page 8 for correct
gas pressure settings and fig. 7 for locations where gas
pressures are taken.
4. Btu input is too low due to insufficient gas supply.
Make sure your main gas line is fully opened. If using LP
gas, be sure that the size of the propane tank is adequate to
supply the required gas pressure.
5. Cold water is mixing with the hot water between the
Bosch and the outlet.
Compare water temperature at outlet of the Bosch (hold the
Bosch's outlet pipe with your hand) and at the tap. If these
two are very different, check for mixing valve or plumbing
crossover (see "NO SPARK AT THE PILOT" paragraph #4).
Where automatic "anti-scald" valves are required by code,
lower the temperature setting on the Bosch as much as
possible and balance the pressure between cold and hot
water after the Bosch.
11

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