Hydronic Heating Boilers and Domestic Water Heaters Installation and Service Manual

Installation and
Service Manual
39
Remember, no water heating system provides exact
temperatures at all times. Let the system operate a few days at
your desired settings to determine correct settings for your
needs.
1. These units are equipped with an operating temperature
control.
2. The control set points are preset to a low test setting when
shipped from the factory.
3. Reset the temperature set points to the lowest settings
which will satisfy hot water demands, eliminate a possible
condensate problem and prevent a risk of scald injury.
 WARNING: Return water temperatures
must not be less than 140°F (60°C). If lower
return wate temperatures are required, folllow
the instructions for Low Temperature Return
Water Systems, page 25.
4. The High-Fire Offset should normally be adjusted to “0”
when supplying potable hot water for domestic use.
5. Stage firing can be achieved by adjusting the High-Fire
Offset to any value other than zero. Typically, a setting of
3°F is 5°F is suitable for stage firing in a water heater
application. Stage firing of a potable water heater is
normally only used to replace system standby heat loss.
6. All stages of burner operation should fire when there is a
major draw from the potable hot water storage system.
This prevents possible condensate problems and ensures a
rapid recovery of the hot water used.
Note: The High-Fire stage will be delayed by approximately
10 seconds to allow a soft start of the water heater.
IMPORTANT: When water is stored at
temperatures above 125°F (52°C), a thermostatic
mixing valve must be installed on the hot water
outlet from the storage tank to supply lower
temperature water and prevent the risk of a scald
injury.
Note: This water heater, when set at a lower temperature
setting, is not capable of producing hot water of sufficient
temperature for sanitizing purposes.
Location of Cold Water Supply Piping
Connections
Incorrect piping of the cold water supply to the system may
result in excessive low temperature operation causing
condensate formation on the heat exchanger and operational
problems. You must install the cold water supply piping in the
discharge piping from the heater to the storage tank. This
allows the cold water to be tempered in the storage tank before
entering the heater. See Figure 41 and typical installation
drawings provided with the unit for correct piping. Higher
water temperatures reduce condensate formation.
 WARNING: Should overheating occur or
the gas supply fail to shut off, do not turn off or
disconnect the electrical supply to the pump.
Instead, shut off the gas supply at a location
external to the unit.
High Water Temperature Limit Control
The unit is equipped with an adjustable setting, auto-reset high
water temperature limit control. The hot water heater
temperature limit control has a maximum limit setting of
200°F (93°C). If water temperature exceeds the set point, the
limit will break the control circuit and shut down the unit. The
limit control will only be reset after the water temperature has
cooled below the set point of the limit. The high water
temperature limit control is mounted in the outlet side of the
front header. A manual reset high water temperature limit
control is available as an optional control.
Optional Relief Valve
This water heater is normally supplied with a temperature and
pressure relief valve(s) sized in accordance with applicable
codes. Units may be supplied with an optional pressure only
relief valve(s). When a water heater equipped with this
optional relief valve is piped to a separate storage vessel, the
storage vessel MUST have a properly installed temperature
and pressure relief valve which complies with local codes.
Thermal Expansion
A relief valve which discharges periodically may be due to
thermal expansion in a closed system. A hot water supply
boiler installed in a closed system, such as one with a backflow
preventer or check valve installed in the cold water supply,
shall be provided with means to control expansion. Contact the
water supplier or local plumbing inspector on how to correct
this situation. Do not plug or cap the relief valve discharge!
Cathodic Protection
Hydrogen gas, which is extremely flammable, can be produced
in a hot water system that has been unused for a long period of
time (generally two weeks or more). To prevent the possibility
of injury under these conditions, open the kitchen sink hot
water faucet for several minutes before using any electrical
appliance connected to the hot water system. If hydrogen is
present, there will be an unusual sound such as air escaping
through the pipe as the hot water begins to flow. Do not smoke
or have open flames near the faucet at this time.