Lochinvar HS 50 Series 100, User'S Information Manual

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uniformly linked. As water fl ow is decreased the temperature 
rise will increase and as water flow is increased the 
temperature rise will decrease. Because of this relationship 
between temperature rise and fl ow rate this test can be 
useful to determine if the flow rate through the heat 
exchanger is adequate. Other factors may also aff ect water 
fl ow rate and temperature rise such as debris or lime scale 
build up inside heat exchanger or water pump operation.

If the temperature rise through the HPWH is consistently 
lower than 8°F the outlet (supply) valve can be throttled 
slightly closed to reduce the water fl ow rate. This may be 
necessary on installations with a minimum of water piping 
between the HPWH and the water system or tank.

Throttling should be done in small increments, no more 
than 1/8 turn of the valve handle at a time. The HPWH 
must be allowed to run for approximately 5 minutes 
between each adjustment before the temperature rise 
is measured again. If the outlet valve is throttled during 
start up, mark the valve position and remove the valve 
handle to ensure it is not accidentally changed.

If the temperature rise through the HPWH is consistently 
greater than 12°F the water fl ow may be restricted. Ensure 
all water valves between the HPWH and the tank or water 
system are fully open. Ensure the  e x t e r n a  l  water pump 
is running. If the temperature rise continues to be excessive 
call the toll free technical support phone number: 

1-833-

447-3201

.

5.  Using thermometers or temperature sensors, measure 

the temperature of the incoming source water to the 
HPWH and the outgoing source water leaving the unit. 
The outgoing temperature should be 12°F to 20°F (7°C to 
13°C) cooler than the incoming. The higher the fl ow rate 
the lower the temperature diff erential will be

6.  When all of the above procedures are complete adjust 

the tank temperature control set point to desired system 
temperature, not to exceed 150°F (66°C). Remove all test 
instruments and replace all cabinet doors.

GOAL:

 Achieve a 3-4 GPM fl ow rate through the condenser by 

using the lower limit input.

WHY:

 Every piping system is diff erent therefore they have 

diff erent head losses in the system. In order for the Lochinvar 
heat pump to operate effi

    ciently and meet the supply demands 

eff ectively it is important to set the lower limit of the control 
valve to meet the minimum water fl ow rate requirements for 
the heat pump. The optimal fl ow rate is 3-4 GPM which allows 
the unit to sense that there is fl ow, while also maintaining a 
high change in temperature between the entering and leaving 
water. It is strongly advised to write down the control valve 

lower limit for this system in the case that the system must be 
purged again.

HOW: 

1.  Access the confi guration screen on the heat pump hot 

water heater

2.  Input a lower limit value between 20 and 100

3.  Press purge & wait 30 seconds for fl ow in the system to 

become consistent

4.  Observe if the goal of 3-4GPM has been met (this value 

will fl uctuate slightly on the screen)

A.  If the GPM is too high reduce the lower limit value

B.  If the GPM is too low increase the lower limit value

5.  Repeat this process until the goal of 3-4GPM has been 

achieved.

Lower Limit Value: 

___________________

PURGING THE CONDENSER ON A PLC 
WATER HEATER

Access the confi guration screen on the heat pump hot water 
heater. Set the “lower limit” value to 100 to open the control 
valve all the way, then press the purge button to run the pump. 
(The pump will remain running for 2 minutes unless the button 
is pressed again to stop the purge cycle) While the pump is 
running bleed any air out of the water lines. The “CondFlow” 
value will refl ect the fl ow rate through the condenser of the 
unit, the default value is 2 so when it is constantly above 2 the 
unit is fl owing properly.

The unit comes standard with a Johnson Controls A421 Model 
# A421GBF-x controller. This control is used to control the water 
temperature in the tank by supplying a call signal to the Heat 
Pump Water Heater. The control comes with some factory 
settings. 

The A421 control should never be set higher than 

160°F, failure to comply could void the warranty.

Johnson Controls A421 Controller

Model # A421GBF-x

SETTING LOWER LIMIT CONTROL 

VALVE LIMIT FOR SINGLE-PASS

ELECTRONIC TEMPERATURE 

CONTROLS