Bosch WR430-7K - Manuel (Page 19)

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HOT WATE R TE M PE RATUR E
F L U CT UAT E S
1. Unbalanced pressure in waterlines.
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 or
shower heads are free of minerals. Do not add any flow
restrictor to the shower head.
2. Cold water is mixing with the hot water between the
Bosch and the outlet.
See 4 under “NO SPARK AT THE PILOT”.
3. Inlet water pressure is erratic due to inadequate supply
water pressure or saturated pressure tank on well
system.
Check the inlet water pressure. On a private well, raise
minimum pressure setting to 40 psi. Confirm that the
pressure tank is not water logged.
4. Gas pressure is too low.
See page 15 for correct specifications.
WATER IS TOO HOT
1. Check for lime build-up. (See mineral scale p. 16)
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 15, 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 15 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 PI LOT”
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.
6. Parts in water flow valve are corroded so that the
gas passage is not fully opening.
Contact your service person or call:
Canada 1-800-663-8405, U.S.A. 1-800-824-7337.
6. Check Blower Fan. Is it operating when burner comes
on?
7.
Check flapper in outside vent termination for free
movement.