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
4.The electrical Control Box (Fig. 16) may need to be replaced. Contact your service person or call:
Canada
E864_020
Fig. 16 - Electrical wiring diagram
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.
WATER IS TOO HOT
1.Check for lime
2.Temperature Selection too high
Turn the temperature adjustment knob
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
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