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18
PILOT SPARKS CONTINUOUSLY WITH
NO WATER RUNNING
1. Microswitch needs adjustment
If no water is running, but pilot electrode continuously sparks,
the microswitch screw to the water valve needs adjustment.
See Figure 16.
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.
MAIN BURNERS GO OUT DURING HOT
WATER USE
1. Flow rate diminished below activation rate: 0.5 USGM
(2.5 l) in hot position, 1.0 USGM (5 l) in warm position
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. Check gas supply
4. ECO (overheat sensor) tripped due to overheating
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.
6. Check Blower Fan. Is it operating when burner comes
on?
7. Check flapper in outside vent termination for free
movement.
Fig. 16 - Electrical wiring diagram
E864_020
WATER IS TOO HOT
1. Check for lime build-up. (See mineral scale p. 15)
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.)
4. Insufficient water pressure
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 #39, Fig. 19 page 20).
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 14, table 1. 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 14 for
correct gas pressure settings and fig. 11 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.