▶ Check water level in the condensate trap.
Fig. 38 Water level in condensate trap
▶ After filling reassemble all parts in reverse order.
4.12 Domestic hot water recirculation
Although recirculation directly through the tankless water heater is
allowed, temperature stability is improved by recirculating through a
mini-tank as shown in fig. 39. By using the design in fig. 39, there is no
recirculation of hot water through the tankless water heater and
therefore, does not affect the heat exchanger warranty. Direct
recirculation through the tankless water heater is permissible, however,
the heat exchanger warranty is reduced; contact Bosch
Thermotechnology for further installation requirements. The following
drawing is provided to outline one possible recirculation design using
the water heater in conjunction with an Ariston mini tank water heater.
This schematic is for illustration only and must not be used for actual
Installation without appropriate engineering and technical advice from a
properly licensed professional in the locality where the installation is
Fig. 39 Recirculation application
Full port isolation valve
Circulator pump on timer
C 1210 ES/ESC
The use of a small electric mini-tank after heater (4-6 gallon size) should
be used for this application and designed so the pump will circulate the
water through the mini-tank and the building's hot water return loop
only. Timed or thermostatically controlled operation of the pump is
C 1210 ES/ESC
commonly done. Contact Bosch Thermotechnology if further
information is needed.
4.13 Space heating applications
▶ If the set point temperature is above 120°F,
precautions should be taken to protect users of
potable water from scalding.
▶ Propylene glycol may be used for freeze prevention
ONLY on the space heating side of the heat
exchanger. Do not use ethylene glycol (automotive
▶ The use of a flow switch is recommended to ensure
DHW priority and to prevent "cold-blow" situations
when the Bosch tankless water heater is used with an
air-handling system. The flow switch should be used
to disable the blower on the air-handling system when
domestic water is used.
▶ Ensure the primary pump is properly sized to provide
adequate flow for the system heat load.Ensure the
primary pump is properly sized to provide adequate
flow for the system heat load.
For Pump sizing please refer to the pressure drop
curves, fig. 40. Also remember to account for system
piping pressure loss. A minimum of 1.7 GPM is
recommended to provide adequate flow through the
water heater when determining the size of the primary
Bosch tankless water heaters are approved for use in combination DHW
and space heating applications (open-loop setup). These water heaters
are not approved for use in space heating only applications (closed-loop
setup). Bosch supports applications of combination DHW and space
heating in an open loop configuration if plumbed similar to fig. 41. Use of
a Bosch tankless water heater in a combination DHW and space heating
application will result in the product warranty being reduced to 3 years.
Installation instructions | 29
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