Harsco Industrial P-K DURATION II D2DW-30(S/D) Operating instructions

©2015 Harsco Industrial, Patterson-Kelley PN: 1004905970
Printed: 11/11/2015
P-K DURATION II™
D2DW-30(S/D) & D2DW-80(S/D)
(S-Simplex D-Duplex)
INSTANTANEOUS INDIRECT
DOMESTIC HOT WATER SYSTEM
Model #:_______ Serial #______________________
Start-Up Date: _______________________
Harsco Industrial, Patterson-Kelley
155 Burson Street
East Stroudsburg, PA 18301
Telephone: [phone]
Toll Free: 877.728.5351
Facsimile: 570.476.7247
www.harscopk.com
P-K Duration II D2DW-30&D2DW-80
Rev. 1.00 (10/1/2015)

P-K DURATION II ™ Indirect Domestic Water Heating System
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P-K DURATION II ™ Indirect Domestic Water Heating System
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1..... INTRODUCTION ................................................................................................................................................4
2..... SAFETY..............................................................................................................................................................4
2.1 General.............................................................................................................................................4
2.2 Training.............................................................................................................................................5
2.3 Safety Features ................................................................................................................................5
2.4 Safety Labels....................................................................................................................................5
2.5 Safety Precautions ...........................................................................................................................6
3..... INSTALLATION..................................................................................................................................................7
3.1 Receiving and Storage .....................................................................................................................7
3.2 Compliance with Codes....................................................................................................................8
3.3 Setup ................................................................................................................................................8
3.4 Mechanical Connections ..................................................................................................................9
3.5 Electrical Connections....................................................................................................................15
3.6 Pre-Start Check List .......................................................................................................................16
3.7 Safety Checks.................................................................................................................................16
4..... OPERATION.....................................................................................................................................................17
4.1 LOVE Controller..............................................................................................................................17
4.2 Setup of the Electric Valve .............................................................................................................18
5..... MAINTENANCE ...............................................................................................................................................19
5.1 Maintenance and Inspection Schedule ..........................................................................................19
5.2 Troubleshooting..............................................................................................................................19
6..... PARTS/TECHNICAL SUPPORT .....................................................................................................................21
6.1 RECCOMENDED SPARE PARTS.................................................................................................21
6.2 Wiring Diagram...............................................................................................................................22
6.3 Models............................................................................................................................................23

P-K DURATION II ™ Indirect Domestic Water Heating System
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1 INTRODUCTION
This manual describes the installation and operation of the P-K Duration II Semi-instantaneous indirect domestic
hot water system. It is important to note that the P-K Duration II is designed to operate in conjunction with a
complete hydronic system and does require an external source of hot boiler water. The available boiler water
temperature will have a profound impact on the performance and capacity of the P-K Duration II, and it must
always exceed the desired domestic hot water supply temperature.
If you have any questions on the information contained within, or do not fully and completely understand the
content, please contact Harsco Industrial, Patterson-Kelley Technical Service at 570.476.7261 or toll free at
877.728.5351.
The P-K Duration II system is only a part of a complete water heating system. This add-on package may be fully
operational and yet because of poor circulation, control, or other operating characteristics not deliver hot water to
the desired location. Additional equipment such as pumps, flow switches, balancing valves, and check valves
may be required for satisfactory operation of any system. Harsco Industrial, Patterson-Kelley cannot be
responsible for the design or operation of such systems and a qualified engineer or contractor must be consulted.
2 SAFETY
2.1 GENERAL
The P-K Duration II instantaneous indirect domestic hot water system must be:
Installed, operated, and serviced in accordance with instructions contained in this manual and other
supplemental manuals.
Installed by qualified personnel in accordance with designs prepared by qualified facility engineers including:
structural, mechanical, electrical, and other applicable disciplines.
Operated and serviced in accordance with a comprehensive safety program determined and established by
the customer. Do not attempt to operate or service until such a program has been established.
Operated and serviced by experienced, qualified, and properly trained personnel in accordance with all
applicable codes, laws, and regulations.
NOTICE! Each safety device must be maintained and checked per the recommended schedule. Refer to
Section 3.7 of this manual.
The P-K Duration II is a dynamic system that is designed to heat domestic hot water to
a wide range of temperatures. The P-K Duration II system is capable of heating water to scalding temperatures.
Refer to your local codes for guidelines on compliance for domestic hot water systems. A thermostatic mixing
valve or other device may be required to prevent scalding.

P-K DURATION II ™ Indirect Domestic Water Heating System
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2.2 TRAINING
Proper training is the best protection against accidents. Factory training sessions are available to qualified
individuals who are sponsored by the local Harsco Industrial, Patterson-Kelley representative.
It is essential to read, understand, and follow the
recommendations of this manual before installing,
operating, or servicing this equipment. Failure to do so
could result in fire or explosion and serious injury, death,
and/or property damage.
Operating and service personnel must be thoroughly familiar with the basic construction of the P-K Duration II
system, the location and operation of the controls, adjustment of their various mechanisms, and all applicable
safety precautions. If any of the provisions of this manual are not fully and completely understood, contact
Harsco Industrial, Patterson-Kelley Technical Service at 570.476.7261 or toll free at 877.728.5351.
2.3 SAFETY FEATURES
It is the responsibility of the customer to maintain the safety features, such as but not limited to: guards, safety
labels, safety controls, interlocks, lockout devices and pressure relief valves.
2.4 SAFETY LABELS
The following words are used in this manual to de-note the degree of seriousness of the individual hazards.
Indicates an imminently hazardous situation which, if not avoided, will result in death
or serious injury. This signal word is to be limited to the most extreme situations.
Indicates a potentially hazardous situation which, if not avoided, could result in death
or serious injury.
Indicates a potentially hazardous situation which, if not avoided, may result in minor or
moderate injury. It may also be used to alert against unsafe practices.
NOTICE/NOTE - NOTICE is the preferred signal word to address practices not related to personal injury. The
safety alert symbol is not used with this signal word.

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2.5 SAFETY PRECAUTIONS
Provide a suitable location for the P-K Duration II system, away from normal personnel traffic, with adequate
working space, adequate clearances, proper ventilation and lighting, with a structure sufficiently strong and rigid
to support the weight of the P-K Duration II system, all piping, and accessories.
2.5.1 Electrical Hazards
Shock hazard! Properly lockout/tag out the electrical service and all
other energy sources before working on or near the P-K Duration II.
Shock hazard! Do not spray water directly on this system or on any
electrical components.
Electrical hazard! Do not alter wiring connections.
2.5.2 Burn, Fire, and Explosion Hazards
Burn hazard! Possible hot surfaces. Pipes and internal components could be hot.
Do not touch piping or internal components during operation or immediately after
shutdown of the boiler.
Burn hazard! Hot fluids. Use caution when servicing or draining the P-K Duration
II system.
Isolation valves are provided on all inlets and outlets for your convenience. Close
the applicable isolation valves and allow the P-K Duration II to cool down to
ambient temperature before servicing.
The P-K Duration II is a dynamic system that is designed to heat domestic hot water to
a wide range of temperatures. The P-K Duration II system is capable of heating water to scalding temperatures.
Refer to your local codes for guidelines on compliance for domestic hot water systems. A thermostatic mixing
valve or other device may be required to prevent scalding.
2.5.3 Crush Hazards
Lifting hazards! Use properly rated lifting equipment to lift and position the P-K
Duration II system. The load is unbalanced. Test balance before lifting 3 ft. above
the floor. Do not allow personnel beneath the lifted load. Refer to approximate
weights in the table.
Model
Weight in Pounds
D2DW-30S Simplex
950 lbs.
D2DW-30D Duplex
1590 lbs.
D2DW-80S Simplex
1005 lbs.
D2DW-80D Duplex
1700 lbs.
Hot Surface
General Warning
General Warning

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2.5.4 Chemical Hazards
•Chemical hazards from cleaning products. Use caution when cleaning the system.
The use of professional assistance is recommended. Use safe procedures for the
disposal of all cleaning solutions.
2.5.5 Pressure Hazards
Pressure hazard! Hot fluids. Isolation valves are provided on all inlets and outlets for
your convenience. Make sure all isolation valves are closed before servicing.
Pressure hazard! Hot fluids. Annually test safety relief valve for proper operation.
Do not operate with faulty relief valve(s).
2.5.6 Slip, Fall Hazards
Tripping hazard! Do not install piping on floor surfaces. Maintain clear path around
the P-K DURATION II™system.
Slip and fall hazard! Use drip pan to catch water while draining. Maintain dry floor
surfaces.
Fall hazard! Do not stand on the P-K DURATION II™ system.
3 INSTALLATION
Installation and service must be performed by a qualified installer, service agency,
or gas supplier.
3.1 RECEIVING AND STORAGE
3.1.1 Initial Inspection
Upon receiving the P-K Duration II system, inspect it for signs of shipping damage. Since some damage
may be hidden, unpack the product, open the front, and side doors to inspect. Verify that the total number of
pieces shown on the packing slip agrees with those actually received.
NOTICE! Note any damage, suspected potential damage, or shortage of materials on the freight bill and
immediately notify the carrier. File all claims for shortage or damage with the carrier. Claims for hidden damages
must be filed with your carrier within 7 days.
3.1.2 Storage Prior to Installation
If the P-K Duration II system is not installed immediately, it must be stored in a location adequately protected from
the weather, preferably indoors. If this is not possible, then it should remain in the shipping container and be
covered by a tarpaulin or other waterproof covering.
NOTICE! Controls and other equipment that are damaged or fail due to weather exposure are not covered by
warranty.
General Warning
General Warning
General Warning

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3.2 COMPLIANCE WITH CODES
The brazed plate heat exchanger is constructed and stamped in accordance with ASME Boiler and Pressure
Vessel Code, Section VIII, Division 1 for 219 psig maximum operating pressure. However, certain components in
the domestic piping have a maximum pressure rating of 150 psig. Therefore, the domestic side pressure must
never exceed 150 psig.
The pressure-only relief valve in the domestic piping is constructed and stamped in accordance with ASME Boiler
and Pressure Vessel Code, Section VIII with a standard 150 psig set pressure.
3.3 SETUP
3.3.1 Foundation and Placement
Provide a firm, level foundation, preferably of concrete. The P-K Duration II system must be level to function
properly. Consult with a certified Professional Engineer regarding any seismic anchoring requirements.
3.3.2 Clearances
Since the P-K Duration II instantaneous indirect domestic hot water system is designed to operate in potentially
remote mechanical rooms, it requires sufficient clearance for service and operation.
3.3.2.1 Clearance Figure
Clearance Dimensions
A
24”
B
18”
C
36”
B

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3.4 MECHANICAL CONNECTIONS
The P-K Duration II system is designed to provide substantial domestic hot water capacity in a 32” wide x 64” long
footprint and requires four (4) piping connections to operate as seen below:
A. DHW Supply (2” Sweat Ball Valve)
B. DHW Return (2” Sweat Ball Valve) C. Boiler Water Inlet (2” NPT Ball Valve/Grooved) D. Boiler Water Outlet (2” NPT Ball Valve/Grooved)
3.4.1 Connection Figure
A
B
D
C
A
B
C
D
Simplex Model
Duplex Model

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3.4.2 Boiler Piping (Simplified)
The energy source for the P-K Duration II system is hot boiler water from the hydronic system and is regulated by
an electronic control valve. By default, this control valve is setup to operate as a 3-way valve since this is the
recommended and preferred operating method. By closing the isolation valve below the control valve, it is also
possible to operate this as a 2-way valve.
Assuming the Duration II system will be operated with 3-way control valve functionality, when the domestic hot
water supply temperature is satisfied, the control valve bypasses all hot boiler water away from the brazed plate
heat exchanger as shown below with the curved red arrow (middle):
3.4.2.1 Boiler Piping Figure
As the domestic hot water supply temperature drops below the desired setpoint, the control valve actuates
allowing the flow of hot boiler water into the brazed plate heat exchanger as shown above with the curved orange
arrow (Left). As the DHW supply temperature drops below setpoint, the control valve allows more boiler water to
enter the heat exchanger.
During this process, heat is transferred from the boiler water to the colder domestic water, reducing the outgoing
boiler water temperature. As the DHW supply temperature approaches setpoint, the 3-way control valve will
restrict the flow through the heat exchanger and will bypass more boiler water.
The boiler water flows through a grooved wye strainer. This helps protect the brazed plate heat exchanger from
foreign debris which will reduce its efficiency. The strainer is recommended to be cleaned every 6 months.

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3.4.3 Boiler Water Manifold Piping (Duplex Only)
The Duration II Duplex unit is equipped with a Boiler Water Manifold to allow for easy installation. Below is an
image which shows the manifold. The Boiler water is piped to each heat exchanger from one connection point,
limiting the requirement for multiple connections, provided the same boiler water is required to feed both heat
exchangers. In a situation where the boiler water is coming in from the left side, removing the grooved tee fitting
and rotating the manifold is easily complete.
3.4.3.1 Boiler Water Manifold Piping Figure

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3.4.4 Domestic Water Piping (Simplified)
The P-K Duration II system features constant recirculation on the domestic hot water piping. This circulation
pump offers 3-speed operation that can be selected by the operator. Constant circulation on the domestic hot
water side offers several advantages:
“Primes” the DHW loop ensuring the discharge water is at the correct temperature.
Maintains accurate temperature readings by maintaining flow across the temp gauges and RTD.
Minimizes heat exchanger scale formation by maintaining velocity across the plates.
Inhibits bacterial growth by preventing stagnant water conditions.
As domestic hot water is consumed throughout the building, hot water will exit the Duration II in the lower copper
piping (red arrow) and fresh makeup water will enter in the upper copper piping (blue arrow). The recirculation
pump circulates water through the heat exchanger to reduce the amount of hot spots that may form on the heat
exchanger, and keep the velocity to prevent scale build it. The recirculation path is indicated by the orange arrow
(Middle).
3.4.4.1 Domestic Water Piping Figure

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3.4.5 Example Domestic Hot Water Installation
It is important to note that the P-K Duration II indirect domestic water heating system does not require a domestic
water storage tank, if hot water is constantly available for the 3-way valve. If using in conjunction with a boiler, the
initial call for heat takes time until the boiler operates at maximum power. If the unit is used in this manner, the
storage tank needs to be sized appropriately for the application.
3.4.5.1 Example Piping Diagram

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3.4.6 Relief Valve Discharge Piping
The Pressure Only relief valve discharge pipe is routed towards the floor. Refer to your local code enforcement to
ensure compliance with relief valve discharge piping. DO NOT connect any valves in the relief valve discharge
piping.
3.4.6.1 Relief Valve Discharge Pipe
3.4.7 Flushing the Domestic Water
Flush the domestic water periodically by using the drain valve located on the DHW supply line (Bottom). At the
same time, the strainer should be checked and cleaned properly.
NOTICE! Under no circumstances should petroleum based cleaning or sealing compounds be used in the boiler
system.
Before the initial fill, ensure that any and all sediment or particulates have been removed from the domestic water.
Ensure that the outlet isolation valve on the P-K Duration II system is closed. Use the drain valve on the domestic
water outlet line to purge sediment and particulates.

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3.4.8 Filling the DHW System
Before filling the system, ensure all the mechanical connections are complete.
STEP 1 –Connect a hose to the drain valve on the domestic water outlet line.
STEP 2 –If applicable, close the manual isolation valves in the domestic piping between the domestic
water storage tank and the P-K Duration II system.
STEP 3 –Open drain valve on domestic piping.
STEP 4 –Slowly open the domestic water inlet ball valve to start the flow of water.
STEP 5 –Close the drain valve on the domestic piping once a steady flow of water occurs.
STEP 6 –Open the cap on the automatic air vent in the domestic water inlet piping.
STEP 7 –Open the manual isolation valves on the outlet of the domestic piping.
STEP 8 –Check for any leaks in all piping connections, especially at the Victaulic couplings. Tighten or
reseat the connections if necessary.
3.4.9 Filling the Boiler System
Before filling the system, ensure all the mechanical connections are complete.
STEP 1 –Connect a hose to the drain valve on the boiler water strainer valve.
STEP 2 –Open drain valve on domestic piping.
STEP 3 –Slowly open the boiler water outlet ball valve to start the flow of water.
STEP 4 –Close the drain valve on the boiler water strainer once a steady flow of water occurs..
STEP 5 –Open the manual isolation valves on the inlet of the boiler piping.
STEP 6 –Check for any leaks in all piping connections, especially at the Victaulic couplings. Tighten or
reseat the connections if necessary.
3.5 ELECTRICAL CONNECTIONS
Only after all the mechanical connections have been completed and verified should any electrical connection be
made. Please refer to Section 6.1 for a wiring diagram of the P-K Duration II system.
NOTICE! A dedicated earth ground (green wire) is required. Do not ground through the conduit.
The P-K Duration II system requires 120 volt, single phase, 60 hertz electrical service (15 amps). Size the supply
circuit accordingly.
NOTICE! Be sure to properly lockout/tagout the Duration II for any electrical work that needs to be made.
3.5.1 Incoming Power Line
The control panel is located and accessed on the front of the P-K Duration II system. The 120 volt, single phase,
60 hertz, 15 amps electrical service should be routed to this panel. Knockouts are located in the rear of the panel.
3.5.2 High Voltage
The P-K Duration II has inputs for line voltage (120vac) connections.
120 VAC Supply: Connect the incoming power supply directly to the disconnect switch.
3.5.3 Low Voltage
Communication Connection: The controller is capable of MODBUS Communication. A Protocol
Convertor is available to convert from MODBUS to BACNet or LONWORKS.

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oConnect BMS system to LOVE controller on terminals 9 (Data -) and 10 (Data +).
oFor connecting the Protocol Convertor to the system, please refer to the ProtoNode Startup
Guide.
3.6 PRE-START CHECK LIST
Before attempting to start the P-K Duration II system, ensure the following items have been completed.
1. Inspect the P-K Duration II system for leaks in either the boiler side or domestic side piping. Correct any and
all leaks promptly. If leaks occur at grooved fittings, refer to manufacturer’s instructions for more information.
2. Inspect the relief valve discharge piping and ensure this is routed to a nearby floor drain.
3. Ensure there is sufficient clearance around the unit, especially the front for access to control panel.
3.7 SAFETY CHECKS
The following checks of safety systems must be made before putting the P-K Duration II™ system boiler into
normal operation.
Never attempt to operate a P-K Duration II system that has failed to pass all the
safety checks described below.
After checking controls by manual adjustment, make sure they are always reset to
their proper settings.
3.7.1 Test of Circulation Pumps
Once power has been turned on to the Duration II, ensure the domestic water pump is pumping water in the
correct direction (up).
3.7.2 Test of High Temperature Limit Aquastat
When the Duration II is powered on, adjust the dial on the high temperature limit aquastat to the lowest possible
setting. Allow the Duration II to increase the domestic water temperature. Once the domestic water temperature
exceeds this value, the high temperature limit aquastat should open and trigger the safety circuit. When this
happens, the control valve is immediately disabled will close completely, and the circulating pumps will continue
to run during this time in order to dissipate the heat.
If this does not work, check the wiring on the high temperature limit aquastat and ensure there is no jumper or
other wiring attached to the Duration II safety circuit. If necessary, replace the high temperature limit aquastat.

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4 OPERATION
4.1 LOVE CONTROLLER
Read instructions and understand operation before operating or making adjustments
to the digital temperature controller.
A digital temperature controller (right) positions the valve in response to outlet water temperature. A 4-20
milliamp signal drives the valve actuator. The controller uses a type J thermocouple to sense the outlet domestic
water temperature.
The default screen is shown. PV - the top number (red) - is the
temperature of the water in the P-K COMPACT®water heater and SV - the
lower number (green) - is the setpoint.
The index button changes the parameters displayed on the screen.
The PV line lists the parameter name and the SV line lists the parameter
value.
Press the enter button to store any value after it is changed.
The up and down buttons are used to change the values of
the parameters.
4.1.1 Controller Operation
To change the setpoint, press the up or down buttons to change SV to the desired value. Once the desired value
is displayed, press the enter button to store the value.
The temperature control starts in the operation mode. The following table lists the operating parameters, their
factory default settings, and a description of the parameters function. Parameters are accessed by repeatedly
pressing the index key until the desired parameter is displayed.
Operational Mode
Parameter
Default Value
Description of Parameter Function
Home Screen =
Setpoint
120°F
Setpoint temperature of outlet water
r-S
RUN
Run –Stop output control.
Must be in run for control to operate
SP
0
Sets the number of digits to the
right of the decimal point
AL1H
20
Alarm 1 High Set Point,
Alarms at setpoint + AL1H value
LoC
Off
Set front panel security,
Off = no security, On = settings are locked
OUt1
###
Output value of controller, 0 –100%

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4.2 SETUP OF THE ELECTRIC VALVE
The valve should open when the hot water demand increases and close when the hot water demand decreases.
If power is removed, the valve should fail in the closed position. This must be verified
prior to putting the unit in service.
During initial startup, check the DIP switches to verify correct positioning. The DIP switches are found in the valve
actuator. The following pictures illustrate the correct positioning for the various valve actuators.
NOTICE! - For water to water applications or when valve is oversized, equal percentage valves are the preferred
type.
4.2.1 Siemens Valve Actuators MXG and MXF:
All of the Siemens valves have a manual override control knob on the top of the valve actuator. The knob must
be set to “Auto” for the valve to function. The style actuators used is the MXG. The MXG actuator is shown
below.
DIP switches are labeled 1 2 3 and ON is labeled.
Switch
Function
OFF
ON
Factory Setting
1
Valve Response Type
Linear
Equal Percent
ON
2
Control Signal Range
0-10 VDC
2-10 VDC or
4-20 mA
ON
3
Input Selector
0/2-10 VDC
4-20 mA
ON

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5 MAINTENANCE
5.1 MAINTENANCE AND INSPECTION SCHEDULE
Proper lockout/ tag out procedure must be employed when servicing this unit.
Label all wires prior to disconnection when servicing controls. Wiring errors can
cause improper and dangerous operation.
Determine the cause of any lockout or errors before resetting the boiler. If able to
determine cause of lockout, then appropriate corrective action should be taken. If unable to determine cause of
the problem, call a qualified service technician.
Verify proper operation after operation servicing.
5.1.1 Daily
Observe operating temperature and general conditions.
Listen to the performance of the P-K Duration II system.
oIf you hear a “sloshing” noise that means air is present in the system. Ensure the vent cap on the
automatic air vent are open.
oIf the pumps are making noise, ensure they are not deadheaded or cavitating. Refer to Section
5.2 for troubleshooting information.
5.1.2 Weekly
Check for leaks in the boiler piping and the domestic piping. Correct immediately if discovered.
5.1.3 Monthly
Check all relief valves by slightly opening the stem. Once you see a small amount of water exit the
discharge, close the relief valve’s stem. Once the stem is closed, ensure there is no additional water that
exits the relief valve.
Verify the domestic temperature sensor reading is accurate on the Temperature Controller.
Ensure the high temperature limit aquastat is functioning properly.
5.1.4 Annually
The brazed plate heat exchanger can scale up with calcium and other minerals present in the domestic
water. This will inhibit heat transfer and it may be necessary to clean or replace the brazed plate heat
exchanger.
Remove and inspect the circulating pumps for signs of deterioration. Repair or replace if needed.
Clean and inspect the P-K Duration II system for any signs of cracks, leaks, or loose connections. Repair
or replace if needed.
5.2 TROUBLESHOOTING
5.2.1 Circulation Pump Deadhead
Deadheading occurs when the circulation pump is unable to deliver any flow. Ensure that any isolation valves
installed in the system are OPEN.

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5.2.2 Circulation Pump Cavitation
Cavitation occurs when the water pressure at the suction side of the pump is below the pump’s required suction
head pressure. Ensure that any isolation valves on the suction side of both circulation pumps are OPEN. Also,
ensure that there is a sufficient static fill pressure of the system.
5.2.3 Poor Heat Transfer
Poor heat transfer can be caused by insufficient flow, insufficient boiler water temperature, or scaling of the heat
exchanger.
Ensure that the boiler side has sufficient flow, as well as the domestic side, and that all circulation pumps
are moving water at the desired rate. (Boiler pump supplied by others)
Next, increase the boiler supply temperature in small increments to ensure there is sufficient temperature
to produce the desired domestic water temperature. If these two steps are unable to restore heat
transfer, it may be necessary to clean or replace the brazed plate heat exchanger.
5.2.4 Erratic temperature control
Check for proper operation of the temperature control.
Check for proper rotation of integral circulation pump.
Check for flow of circulator pump. (Be sure water is flowing through the recirculation pipe)
Check valves in pipe line must be operational.
Check for proper boiler water flow.
5.2.5 Domestic water temperature is too high or too low.
Check the setting of the temperature control.
Check temperature sensing element for malfunction.
Check for proper boiler water temperature and flow rate.
Check to be sure heater design rating is not being exceeded.
5.3 HEAT EXCHANGER CLEANING
AIC brazed plate heat exchangers operate with high turbulence flow, even at low flow rates. This high turbulence
keeps small particles in suspension minimizing fouling and scaling. However, in some applications the fouling
tendency can be very high, e.g. when using extremely hard water at high temperatures. In such cases it is always
possible to clean the exchanger by circulating a cleaning liquid. Use a tank with weak acid, 5% phosphoric acid
or, if the exchanger is frequently cleaned, 5% oxalic acid. Pump the cleaning liquid through the exchanger. For
optimum cleaning, the cleaning solution flow rate should be 1.5 times the normal flow rate, preferably in a back-
flush mode. After use, do not forget to rinse the heat exchanger carefully with clean water. A solution of 1-2%
sodium hydroxide (NaOH) or sodium bicarbonate (NaHCO3) before the last rinse ensures that all acid is
neutralized. Clean at regular intervals.