Raypak MVB 504A Installation & Operating Manual page 14

inlet to increase the heater inlet temperature above
120°F (49°C). This precautionary measure should pre-
vent the products of combustion from condensing
beyond the ability of the condensate management sys-
tem employed in this heater in most installations.
Warranty claims will be denied for damage or fail-
ures caused by condensation.
Cold Water Starts
Cold water starts, where the inlet water temperature
remains below 120°F (49°C) must have cold water
start protection. Known protection methods consist
of mixing heated outlet water with the inlet water using
a bypass to raise the inlet to 120°F (49°C) or higher.
Once the system is heated up and has return water
temperatures of 120°F (49°C) or higher, the mixing of
outlet water with inlet water is no longer needed and
the bypass can be shut off. If the bypass is not shut off
as the system heats up, the outlet temperature may
continue to climb and trip the high limit, thereby shut-
ting down the heater. Thus an automatic valve system,
such as a three-way proportional valve to control the
bypass, should be used.
*Maximum 4 times the pipe diameter or 12", whichever is less.
Fig. 9: Cold Water Start
Cold Water Run
Cold water run differs from cold water start in that the
system water entering the heater remains below
120°F (49°C) continuously. Typically, this is the case in
swimming pool heating and water source heat pump
applications, as well as some others. If the system
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water is kept in a narrow temperature range of no
more than 10°F (5°C), a permanent manual bypass
can be employed and manually adjusted to achieve an
inlet temperature of 120°F (49°C) or higher as adjust-
ed at the minimum temperature in this narrow
temperature range (i.e. Range 75°F to 85°F – adjust
bypass with temperature at 75°F (24°C)) so that when
temperature is 85°F (29°C), minimum inlet tempera-
ture would be 130°F (54°C). An injector pump
arrangement may also be utilized to keep the heater
loop at or above 120°F (49°C). An injector pump
arrangement may be used to keep the heater loop at
or above 120°F (49°C). An injector pump approach
has the added value of being able to adjust automati-
cally to changes in the system water coming back to
the heater.
*Maximum 4 times the pipe diameter or 12", whichever is less.
Fig. 10: Cold Water Run
"H" Bypass
Adjustment of the manual bypass valve is critical to
proper operation of the heater. The manual bypass
valve should be adjusted to achieve a minimum inlet
water temperature of 105°F (40°C) for Pool Heater (P)
versions and 120°F (49°C) for Hydronic Heating (H7)
or Domestic Hot Water (WH7) versions and a system
supply water temperature below 140°F (60°C). When
starting with a cold pool, make initial adjustments.
Make final adjustments when pool water approaches
desired temperature.
For the H-bypass, use the following instructions to set
the manual bypass:
1. Turn on pump.
2. Turn on heater and wait until heater goes to full
fire.
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