U.S. Boiler Company MegaSteam MST Service manual

103536-01 - 3/11
As an ENERGY STAR®Partner,
U.S. Boiler Company
has determined that the
MST288, MST396, MST513 and
MST629 meet the
ENERGY STAR®
guidelines for Energy
efciency established by the
United States Environmental
Protection Agency (EPA).
Price - $5.00
DNAGNITAREPO,NOITALLATSNI
ROFSNOITCURTSNIECIVRES
™maetSageM
RELIOBLIOSSAP-3
gnikeesnehW.reilppusliororotcartnocgnitaehruoyllac,reliobotsriaperroecivresroF
gnitaRnonwohssarebmuNlaireSdnarebmuNledoMrelioBedivorp,reliobnonoitamrofni
.reliobehtfopotnodetacollebaL
rebmuNledoMrelioB rebmuNlaireSrelioB etaDnoitallatsnI
TSM
rotcartnoCgnitaeH rebmuNenohP
sserddA
9700609

2
IMPORTANT INFORMATION - READ CAREFULLY
The following terms are used throughout this manual to bring attention to the presence of hazards
of various risk levels, or to important information concerning product life.
DANGER
Indicates an imminently hazardous situation
which, if not avoided, will result in death, serious
injury or substantial property damage.
CAUTION
Indicates a potentially hazardous situation which,
if not avoided, may result in moderate or minor
injury or property damage.
WARNING
Indicates a potentially hazardous situation which,
if not avoided, could result in death, serious injury
or substantial property damage.
NOTICE
Indicates special instructions on installation,
operation, or maintenance which are important
but not related to personal injury hazards.
NOTICE
This boiler has a limited warranty, a copy of which is included with this boiler.
The warranty for this boiler is valid only if the boiler has been installed, maintained and operated in
accordance with these instructions.
Surface rust on cast iron sections may be attributed to the manufacturing process as well as condensation
during storage. Surface rust is normal and does not affect the performance or longevity of a boiler.
All boilers must be installed in accordance with National, State and Local Plumbing, Heating
and Electrical Codes and the regulations of the serving utilities. These Codes and Regulations
may differ from this instruction manual. Authorities having jurisdiction should be consulted
before installations are made.
In all cases, reference should be made to the following Standards:
USA BOILERS
A. Current Edition of American National Standard ANSI/NFPA 31, “Installation of Oil
Burning Equipment”, for recommended installation practices.
B. Current Edition of American National Standard ANSI/NFPA 211, “Chimneys, Fireplaces,
Vents, and Solid Fuel Burning Appliances”, For Venting requirements.
C. Current Edition of American Society of Mechanical Engineers ASME CSD-1, “Controls and
Safety Devices for Automatically Fired Boilers”, for assembly and operations of controls
and safety devices.
D. All wiring on boilers installed in the USA shall be made in accordance with the National
Electrical Code and/or Local Regulations.

3
DANGER
DO NOT store or use gasoline or other ammable vapors or liquids in the vicinity of this or any other
appliance.
WARNING
Improper installation, adjustment, alteration, service or maintenance can cause property damage, personal
injury or loss of life. Failure to follow all instructions in the proper order can cause personal injury or
death. Read and understand all instructions, including all those contained in component manufacturers
manuals which are provided with the boiler before installing, starting-up, operating, maintaining or servicing
this boiler. Keep this manual and literature in legible condition and posted near boiler for reference by
owner and service technician.
This boiler requires regular maintenance and service to operate safely. Follow the instructions contained
in this manual.
Installation,maintenance, andservicemustbeperformedonlybyanexperienced, skilledandknowledgeable
installer or service agency.
All heating systems should be designed by competent contractors and only persons knowledgeable in
the layout and installation of hydronic heating systems should attempt installation of any boiler.
Installation is not complete unless a safety valve is installed into 1½" x ¾" NPT reducing bushing, mounted
into rear section boss, at the back of rear section. See Unit-Pak Boiler Assembly and Steam Boiler Trim
& Piping Sections of this manual for details.
It is the responsibility of the installing contractor to see that all controls are correctly installed and are
operating properly when the installation is completed.
This boiler is suitable for installation on combustible ooring. Do not install boiler on carpeting.
Do not tamper with or alter the boiler or controls.
Inspect ueways at least once a year - preferably at the start of the heating season. The inside of
the combustion chamber, the vent system and boiler ueways should be cleaned if soot or scale has
accumulated.
When cleaning this boiler, take precaution to avoid damage to burner swing door insulation. If damaged,
or if there is evidence of previous damage, burner swing door insulation must be replaced immediately.
Oil Burner and Controls must be checked at least once a year or as may be necessitated.
Do not operate boiler with jumpered or absent controls or safety devices.
Do not operate boiler if any control, switch, component, or device has been subject to water.
Appliance materials of construction, products of combustion and the fuel contain alumina, silica, heavy
metals, carbon monoxide, nitrogen oxides, aldehydes and/or other toxic or harmful substances which
can cause death or serious injury and which are known to the state of California to cause cancer, birth
defects and other reproductive harm. Always use proper safety clothing, respirators and equipment when
servicing or working nearby the appliance.

4
WARNING
This boiler contains very hot water under high pressure. Do not unscrew any pipe ttings nor attempt
to disconnect any components of this boiler without positively assuring the water is cool and has no
pressure. Always wear protective clothing and equipment when installing, starting up or servicing this
boiler to prevent scald injuries. Do not rely on the pressure and temperature gauges to determine the
temperature and pressure of the boiler. This boiler contains components which become very hot when
the boiler is operating. Do not touch any components unless they are cool.
This boiler must be properly vented. The chimney must be inspected for any obstructions and cleaned
prior to each heating season. A clean and unobstructed chimney ue is necessary to produce the minimum
draft required to safely evacuate noxious fumes that could cause personal injury or loss of life. Evidence
of loose debris and or condensate induced stains at the base of the chimney ue, connector or smokepipe
joints may be signs of condensing ue gases. Flue gas condensate is corrosive, which requires special
consideration and must be addressed immediately. Refer to Section V, "Venting and Air Intake Piping".
This boiler needs fresh air for safe operation and must be installed so there are provisions for adequate
combustion and ventilation air.
This boiler is supplied with controls which may cause the boiler to shut down and not re-start without
service. If damage due to frozen pipes is a possibility, the heating system should not be left unattended in
cold weather; or appropriate safeguards and alarms should be installed on the heating system to prevent
damage if the boiler is inoperative.
This boiler is designed to burn No. 2 fuel oil only. Do not use gasoline, crankcase drainings, or any oil
containing gasoline. Never burn garbage or paper in this boiler. Do not convert to any solid fuel (i.e.
wood, coal). Do not convert to any gaseous fuel (i.e. natural gas, LP). All ammable debris, rags, paper,
wood scraps, etc., should be kept clear of the boiler at all times. Keep the boiler area clean and free of
re hazards.
All boilers equipped with burner swing door have a potential hazard which, if ignored, can cause severe
property damage, personal injury or loss of life. Before opening swing door, unplug burner power cord
from receptacle located in lower right corner of jacket front panel and turn off service switch to boiler
to prevent accidental ring of burner outside the combustion chamber. Be sure to tighten swing door
fasteners completely when service is completed.
I. Pre-Installation ............................................7
II. Unit-Pak Boiler Assembly ............................9
III. Steam Boiler Piping & Trim.........................24
IV. Tankless & Indirect Water Heater Piping.....26
V. Venting & Air Intake Piping ........................29
VI. Electrical .....................................................33
VII. Oil Piping ...................................................41
TABLE OF CONTENTS
VIII. System Start-Up ...........................................43
IX. Maintenance & Service Instructions ............49
X. Boiler Cleaning ............................................52
XI. Trouble Shooting .........................................54
XII. Repair Parts..................................................56
Appendix A - Figures....................................69
Appendix B - Tables......................................71

5
Figure 1: MST288 Thru MST629 Steam Boiler with and without Tankless Heater (Beckett Burner Shown)

6
TABLE 1A: DIMENSIONAL DATA (SEE FIGURE 1)
TABLE 1B: RATING DATA
Boiler
Model No.
Dimensions (See
Figure 1)
Water Content (To Normal
Water Line) - Gallons Heat Transfer
Surface Area
- sq. Ft.
Actual Shipping
Weight (LB.)
"A" "B" "C" With Tankless
Heater Non-Heater
MST288 22-5/8" 24" 6" 15.3 14.9 20.29 607
MST396 22-5/8" 24" 6" 15.3 14.9 20.29 607
MST513 28-5/8" 30" 6" 19.7 19.3 27.29 744
MST629 34-5/8" 36" 7" 24.1 23.8 34.29 881
NOTE: 1: Maximum Working Pressure: Steam - 15 PSI
Boiler
Model
No.
Burner Capacity I=B=R NET
Ratings
Minimum Chimney
Requirements AFUE
%
GPH MBH DOE Heating
Capacity MBH
Steam
MBH
Steam
Sq. Ft.
Round
In. Dia.
Rectangle
In. x In.
Height
Ft.
MST288 0.75 105 92 69 288 6 8 X 8 15 86.0
MST396 1.05 147 127 95 396 6 8 X 8 15 86.0
MST513 1.35 189 164 123 513 7 8 X 8 15 86.0
MST629 1.65 231 201 151 629 7 8 X 8 15 86.0

7
Figure 2: Minimum Installation Clearances To Combustible Materials (Inches)
A. INSPECT SHIPMENT carefully for any signs of
damage.
1. All equipment is carefully manufactured, inspected
and packed. Our responsibility ceases upon delivery
of crated boiler to the carrier in good condition.
2. Any claims for damage or shortage in shipment
must be led immediately against the carrier by the
consignee. No claims for variances from, or shortage
in orders, will be allowed by the manufacturer
unless presented within sixty (60) days after receipt
of goods.
B. LOCATE BOILER in front of nal position before
removing crate. See Figure 1.
1. LOCATE so that vent pipe connection to chimney
will be short and direct.
2. BOILER IS SUITABLE FOR INSTALLATION
ON COMBUSTIBLE FLOOR. Boiler cannot be
installed on carpeting.
3. FOR BASEMENT INSTALLATION, provide
a solid elevated base, such as concrete, if oor is
not level, or if water may be encountered on oor
around boiler.
4. PROVIDE RECOMMENDED SERVICE
CLEARANCE, if applicable, as follows:
a. Clearance from Jacket Front Panel -
• 24" for servicing burner
• 24" for ueway cleaning (MST288 &
MST396)
• 30" for ueway cleaning (MST513)
• 36" for ueway cleaning (MST629)
b. Clearance from Jacket Left Side Panel -
• 19" for burner swing door, if opened fully
with burner mounted, otherwise 1" with
burner removed
• 12" access clearance to service rear of
boiler if right side clearance is less
than 12"
• 1" minimum if right side clearance is 12" or
larger to access and service rear of boiler.
c. Clearance from Jacket Right Side Panel -
• 6" minimum from external Electrical
Enclosure if left side clearance is 12" or
larger to access and service rear of the boiler
• 24" minimum from rear tankless heater (if
equipped) for servicing and removal of the
heater
d. Clearance from Jacket Rear Panel -
• 12" minimum for rear smokebox cleaning
(Note: This dimension will also be
controlled by horizontal to vertical to
horizontal smokepipe arrangement - See
Figures 2 and 15.)
5. For minimum clearances to combustible materials.
See Figure 2.
SECTION I: PRE-INSTALLATION
NOTES:
1. Listed clearances comply with American National Standard
ANSI/NFPA 31, Installation of Oil Burning Equipment.
2. MegaSteam™ boilers can be installed in rooms with
clearances from combustible material as listed above.
Listed clearances cannot be reduced for alcove or closet
installations.
3. For reduced clearances to combustible material, protection
must be provided as described in the above ANSI/NFPA 31
standard.

8
NOTICE
Clearance to venting is for single wall vent
pipe. If Type L vent is used, clearance may be
reduced to the minimum required by the vent pipe
manufacturer.
C. PROVIDE COMBUSTION AND VENTILATION
AIR. Local and National Codes may apply and should
be referenced.
WARNING
Adequate combustion and ventilation air must
be provided to assure proper combustion and
to maintain safe ambient air temperatures.
Do not install boiler where gasoline or other
ammable vapors or liquids, or sources of
hydrocarbons (i.e. bleaches, fabric softeners,
etc.) are used or stored.
Do not install boiler in laundry room, or, in
vicinity of clothes dryer to prevent inadequate
air supply to burner and lint contamination of
burner air intake openings.
1. Determine volume of space (boiler room). Rooms
communicating directly with the space in which
the appliances are installed, through openings not
furnished with doors, are considered a part of the
space.
Volume(ft3) = Length(ft) x Width(ft) x Height(ft)
2. Determine total input of all appliances in the space.
Add inputs of all appliances in the space and round
the result to the nearest 1000 BTU per hour.
3. Determine type of space. Divide Volume by total
input of all appliances in space. If the result is
greater than or equal to 50 ft3/1000 BTU per hour,
then it is considered an unconned space. If the
result is less than 50 ft3/1000 BTU per hour then the
space is considered a conned space.
4. For boiler located in an unconned space of a
conventionally constructed building, the fresh
air inltration through cracks around windows
and doors normally provides adequate air for
combustion and ventilation.
5. For boiler located in a conned space or an
unconned space in a building of unusually tight
construction, provide outdoor air.
a. Outdoor air for combustion may be provided
with an optional U.S. Boiler Company V8H™
Fresh Air Accessory Kit, (ONLY AVAILABLE
WITH BECKETT BURNER). Metal cover
applications, P/N 611280031. Plastic cover
applications, P/N 102119-01. Refer to Fresh Air
Accessory Kit Instructions for installation and air
intake piping details.
or
b. Outdoor air may be provided with the use of two
permanent openings which communicate directly
or by duct with the outdoors or spaces (crawl or
attic) freely communicating with the outdoors.
Locate one opening within 12 inches of top
of space. Locate remaining opening within 12
inches of bottom of space. Minimum dimension
of air opening is 3 inches. Size each opening per
following:
i. Direct communication with outdoors.
Minimum free area of 1 square inch per
4,000 BTU per hour input of all equipment
in space.
ii. Vertical ducts. Minimum free area of 1
square inch per 4,000 BTU per hour input of
all equipment in space. Duct cross-sectional
area shall be same as opening free area.
iii. Horizontal ducts. Minimum free area of 1
square inch per 2,000 BTU per hour input of
all equipment in space. Duct cross-sectional
area shall be same as opening free area.
Alternate method for boiler located within
conned space. Use indoor air if two
permanent openings communicate directly
with additional space(s) of sufcient volume
such that combined volume of all spaces
meet criteria for unconned space. Size each
opening for minimum free area of 1 square
inch per 1,000 BTU per hour input of all
equipment in spaces, but not less than 100
square inches.
6. Louvers and Grilles of Ventilation Ducts
a. All outside openings should be screened and
louvered. Screens used should not be smaller
than 1/4 inch mesh. Louvers will prevent the
entrance of rain and snow.
b. Free area requirements need to consider the
blocking effect of louvers, grilles, or screens
protecting the openings. If the free area of the
louver or grille is not known, assume wood
louvers have 20-25 percent free area and metal
louvers and grilles have 60-75 percent free area.
c. Louvers and grilles must be xed in the open
position, or interlocked with the equipment to
open automatically during equipment operation.
SECTION I: PRE-INSTALLATION (continued)

9
SECTION II: UNIT-PAK BOILER ASSEMBLY
MegaSteam™ Unit-Pak Boiler Assembly Shipment
Content Check List (see Figure 3)
1. ___ Cast Iron Section/Burner Swing Door/Smoke Box Assembly Mounted on Shipping Skid:
____ MST3 (Rear Section, Heater) – Part # 100566-03 / 100045-01 / 100021-01
____ MST4 (Rear Section, Heater) – Part # 100566-04 / 100045-01 / 100021-01
____ MST5 (Rear Section, Heater) – Part # 100566-05 / 100045-02 / 100021-01
____ MST3 (Rear Section, Non-Heater) – Part # 100567-03 / 100045-01 / 100021-01
____ MST4 (Rear Section, Non-Heater) – Part # 100567-04 / 100045-01 / 100021-01
____ MST5 (Rear Section, Non-Heater) – Part # 100567-05 / 100045-02 / 100021-01
2. ___ Control Carton
____ CG450 LWCO; W/Tankless Heater - Part # 100608-01
____ PS801 LWCO; W/Tankless Heater - Part # 100622-01
____ #67 LWCO; W/Tankless Heater - Part # 100678-01
____ CG450 LWCO; L/Tankless Heater - Part # 100680-01
____ PS801 LWCO; L/Tankless Heater - Part # 100681-01
____ #67 LWCO; L/Tankless Heater - Part # 100679-01
3. ___ Jacket Carton
____ MST3 – Part # 100609-03
____ MST4 – Part # 100609-04
____ MST5 – Part # 100609-05
Figure 3: MegaSteam™ Unit-Pak Boiler Shipment Contents (outside container removed)
4. ___ Part Carton
____ MST3 & 4 - Part # 100615-01
____ MST5 - Part # 100629-01
5. ____ Insulation Wrapper
____ MST3 - Part #100614-03
____ MST4 - Part #100614-04
____ MST5 - Part #100614-05
6. ___ Instruction/Label Bag
____ MST (All Models) – Part # 100617-01

10
A. CAST IRON SECTION ASSEMBLY TAPPINGS
Refer to Table 3 "Purpose of Tappings and Bosses" and
Figure 7.
1. All tappings have factory installed thread protectors.
The thread protectors must be removed prior to
jacket and piping installation.
2. Depending of installation specics and boiler build
ordered, some tappings (front section Optional Front
Return, rear section Indirect Heater Supply and
Indirect Heater Limit) may not be used and must
be plugged before jacket and piping installation.
The appropriate size plugs for above mentioned
tappings, as well as rear section Surface Blowoff
and front section probe type LWCO tappings, are
enclosed into Part Cartons (100615-01 or 100629-
01) and Control Cartons (100678-01 and 100679-
01), supplied as part of MegaSteam™ Unit-Pak
Boiler shipment.
B. REMOVAL OF CAST IRON SECTION/
BURNER SWING DOOR / SMOKE BOX
ASSEMBLY FROM SKID.
WARNING
The Cast Iron Section/Burner Swing Door/Smoke
Box Assembly has a substantial weight. Insure
the travel path to permanent location, as well as
mounting surface at boiler permanent location,
are structurally sound and rated to handle the
boiler weight and water content (refer to Table 1A).
Otherwise, a potentially hazardous situation could
result in death, serious injury and substantial
property damage.
1. Move crated Cast Iron Section/Burner Swing
Door/Smoke Box Assembly and part cartons on the
shipping skid as close to nal permanent location as
possible.
2. Remove all fasteners at crate skid. Lift outside
container. Examine the skid contents for damage due
to shipping and handling.
3. Remove Insulation Wrapper, Control Carton, Jacket
Carton and Part Carton from skid and set aside.
4. Instruction/Label Bag is afxed to Section Assembly
tie rod. Remove the bag and locate MegaSteam™
Boiler Installation, Operating and Service Instruc-
tion manual. READ AND UNDERSTAND ALL
INSTRUCTIONS BEFORE ATTEMPTING
BOILER HANDLING AND INSTALLATION.
5. The Cast Iron Section/Burner Swing Door/Smoke
Box Assembly is secured to shipping skid with four
lag screws. Remove the screws and discard.
6. For manual Cast Iron Section/Burner Swing Door/
Smoke Box Assembly removal prepare one piece of
4” x 4” x 16” lg. (or two pieces of 2” x 4” x 16” lg.)
and two pieces of 1” Sch. 40 black pipe to be used
as handles. Suggested pipe length for each handle is
72” (3-section); 78” (4-section) and 84” (5-section).
7. Place wooden block(s) 12” from rear of skid as
shown. See Figure 4 “ Boiler Removal from Skid”.
8. Insert 1” Sch. 40 black pipe handles thru leg holes in
front and rear section legs. Center rear pipe ends on
wooden block(s). See Figure 4.
9. For best leverage, the pipe handles should extend
48” minimum beyond front section face.
10. Using the pipe handles, lift the Cast Iron Section/
Burner Swing Door/Smoke Box Assembly until
adjustable legs are elevated above the skid deck
boards.
11. Remove the skid from underneath the Cast Iron
Section/Burner Swing Door/Smoke Box Assembly.
12. Lower pipe handles until front adjustable legs touch
the oor. Place wood blocks under front legs, if
required, before lowering, to provide hand clearance.
13. To lower rear of the Cast Iron Section/Burner Swing
Door/Smoke Box Assembly tilt boiler slightly
forward by pushing on smokebox, or, lift pipes
protruding thru rear legs, until wooden block(s) can
be removed (see Figure 4). Slowly allow the weight
of boiler to tilt backward until rear legs rest on oor.
14. If wood blocks were placed under front legs, lift pipe
handles; remove the blocks and lower front legs to
oor. Remove pipe handles.
15. Move Cast Iron Section/Burner Swing Door/Smoke
Box Assembly to permanent position by sliding or
walking.
CAUTION
Do not drop boiler when removing from skid and
moving to permanent position.
C. PROCEDURE TO OPEN, CLOSE AND
SECURE BURNER SWING DOOR.
Throughout this manual you will be instructed to open
and close Burner Swing Door for various reasons.
There is a proper and improper method of closing
and securing the door opened for front jacket panel
installation, inspection, cleaning or eld service. Refer
to Figures 5A, 5B, 5C and paragraphs D “Jacket Front
Panel Installation”, and, F “Closing/Securing Burner
Swing Door” for details.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

11
Figure 4: Boiler Removal from Skid
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

12
Figure 5A: Partial Front View - Burner Swing Door Mounted to Boiler - Fully Closed and Secured
D. JACKET FRONT PANEL INSTALLATION.
In order to install front jacket panel Burner Swing Door
and door mounting bracket need to be removed. As
shipped, the door would open to the left side.
1. To open/remove Burner Swing Door (mounted on
Cast Iron Section/Burner Swing Door/Smoke Box
Assembly) and door mounting bracket for front
jacket panel installation:
a. Loosen but not remove door left side latching
hardware (3/8”-16 x 1-3/4” tap bolt).
b. Loosen and remove door right side latching
hardware (3/8”-16 x 1-3/4” tap bolt and 5/16”
washer) and set aside.
c. Remove door left side latching hardware (3/8”-
16 x 1-3/4” tap bolt and 5/16” washer) and set
aside.
d. Lift the door off mounting bracket and set aside.
e. Remove two 5/16”-18 – ¾” hex head cap screws
securing door mounting bracket to front section
and set aside.
f. Remove door mounting bracket and set aside.
g. Note/mark cap screw bosses on front section
left side; locate/mark similar two bosses directly
opposite on front section right side. These four
front section bosses are front jacket panel and
door mounting bracket attachment points.
See also Figure 7 “Purpose of Tappings & Bosses”.
2. Open Jacket Carton and locate jacket front panel
(has factory attached 1” berglass insulation). See
also “Repair Parts” Section, “Jacket Assembly”
illustration for part identication.
3. Open Part Carton, locate Hardware Bag, remove
two 5/16”-18 x ½” Phillips pan head machine
screws.
4. Place front jacket panel over front section
attachment bosses and align jacket holes with front
section boss holes.
5. Firstly, install two 5/16”-18 x ½” Phillips pan head
machine screws hand tight to secure front jacket
panel right side to casting
6. Secondly, insert 5/16”-18 – ¾” hex head cap
screw thru door mounting bracket upper hole
and upper hole on left side of front jacket panel
simultaneously, and, fasten the bracket and panel to
casting hand tight.
7. Thirdly, insert 5/16”-18 – ¾” hex head cap
screw thru door mounting bracket lower hole
and lower hole on left side of front jacket panel
simultaneously, and, fasten the bracket and panel to
casting hand tight.
8. Finally, tighten both sets of hardware to secure the
bracket and front jacket panel.
9. Inspect berglass rope located on the swing door.
The rope must be evenly distributed around the
perimeter of the door groove and cannot bunch or
overhang. Repair or replace, if the rope is damaged,
or, there is a gap between the rope ends.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

13
Figure 5B: Top View - Burner Swing Door Mounted to Cast Iron Block Assembly (Jacket Removed for Clarity)
10. Inspect burner swing door insulation for damage and
proper type.
By design, for all models, cast bars on front section
between the combustion chamber, and, between the
left and right side 2nd and 3rd pass ueways should
make an impression in door insulation to seal the
chambers.
By design, door insulation on model MST629 will
have two by-pass pockets cast into the insulation
centered on the bar between the combustion
chamber and 3rd pass ueways. By design, door
insulation on models MST288, MST396 & MST513
will not have any by-pass pockets. If insulation is
damaged, or, improper type regarding the pockets, it
must be replaced.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

14
11. Upon inspection completion, lift door and place
integral cast hinge pins into door mounting bracket
slotted holes. Do not close and secure door at this
time, proceed to installing stainless steel ueway
bafes.
12. Locate/remove four #8 x ½” shoulder sheet metal
screws from Hardware Bag, then, install them into
front panel ange holes.
E. FLUEWAY BAFFLE INSTALLATION.
Flueway bafes are enclosed into Part Carton. Bafe
requirements differ by boiler model, see Table 2.
TABLE 2: BAFFLE USAGE
Figure 5C: Top View - Burner Swing Door Fully Closed but Not Properly Secured or Sealed
NOTE: Read caution statement before proceeding.
CAUTION
These bafes will generate higher efciencies
and lower stack temperatures. Under certain
conditions, a lower gross stack temperature
entering the chimney has the potential to
be cooled below the dew point and create
condensate on interior surfaces. Flue gas
condensate is corrosive, which requires
special consideration and must be addressed
immediately.
DO NOT install bafes until you have read
Section V, "Venting" completely.
1. To install ueway bafes, provided in miscellaneous
part cartons, as follows, refer to Figure 6 and
Table 2:
• Models MST396, MST513 and MST629 - To
install ueway bafe in 2nd pass ueway on
left side of boiler, hold bafe with word "Left"
readable at the top. Slide bafe in ueway until
position tab touches ns on right side of 2nd pass
ueway. To install ueway bafe in 2nd pass
Boiler
Model
Baffle Usage
2nd Pass 3rd Pass
MST288 None
MST396 (2)
P/N 100042-01 NoneMST513
MST629
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

15
Figure 6: Flueway Bafe Positioning/Orientation
in Flueways
ueway on right side of boiler, hold bafe with
word "Right" readable at the top. Slide bafe
in ueway until position tab touches ns on left
side of 2nd pass ueway.
F. CLOSING / SECURING BURNER SWING
DOOR.
1. To close and secure Burner Swing Door:
a. From fully open position, rotate the door to the
closed position.
b. Lift door upward into the build-in cast ramp/door
rest (protruding from the bottom of the front
section casting – see Figure 5A).
c. Use one hand to apply pressure directly to the
door to hold it in closed position while re-
installing earlier removed door-latching hardware
(3/8”-16 x 1-3/4” tap bolt and 5/16” washer).
Prior to re-installation, apply a drop of supplied
Anti-seize (pouch provided in Part Carton) to
both tap bolts for rust protection and to facilitate
easy removal, if burner door is to be open for
inspection and service. ALWAYS INSTALL
RIGHT SIDE LATCHING HARDWARE FIRST,
THEN INSTALL EARLIER REMOVED LEFT
SIDE HINGE HARDWARE (3/8”-16 X 1-3/4”
TAP BOLT AND 5/16” WASHER) SECOND.
Apply additional pressure while hand tightening
the hardware as far as possible and then release
the pressure.
NOTICE
When securing burner swing door make sure door
is drawn-in equally on both sides.
d. Use a hand or socket wrench to tighten door
hardware. ALWAYS START WITH RIGHT
SIDE TAP BOLT FIRST. Use an alternating
tightening method from right side tap bolt to
left side tap bolt to tighten door equally, until
sealed, without applying excessive torque.
NEVER TIGHTEN LEFT SIDE TAP BOLT
FIRST, OR, EITHER PIECE OF HARDWARE
100% WITHOUT USING THE ALTERNATING
METHOD DESCRIBED ABOVE. See Figure
5B.
e. Failure to follow the prescribed procedure could
cause thread damage to casting and /or leak at
the door seal. IF LEFT SIDE TAP BOLT IS
TIGHTENED BEFORE RIGHT SIDE TAP
BOLT, RIGHT SIDE OF THE DOOR CAN
NOT BE DRAWN-IN TO PROVIDE AN AIR-
TIGHT SEAL, as shown in Figure 5C. Applying
excessive torque will only cause thread damage.
G. JACKET REAR PANEL INSTALLATION.
1. Locate jacket rear panel (has factory attached 3”
berglass insulation) inside Jacket Carton. See
also “Repair Parts” Section, “Jacket Assembly”
illustration for part identication.
2. Locate and remove from Hardware Bag rear panel
mounting hardware – (2 pcs) 5/16”-18 x 3” lg. tap
studs, (2 pcs) 5/16”-18 plated acorn nuts, (2 pcs)
5/8” x 2-9/32” round spacers and (2 pcs) 5/16”-18 x
½” Phillips pan head machine screws.
3. Locate rear panel two lower attachment bosses on
rear section. See Figure 7 “Purpose of Tappings &
Bosses”.
4. Thread both 5/16”-18 x 3” lg. tap studs, with short
threaded end, into lower attachment bosses on rear
section.
5. Install both 5/8” x 2-9/32” round spacers over tap
studs.
6. Place rear jacket panel over rear section, so both
tap studs clear thru lower panel holes, rear section
cleanout openings clear thru matching panel cutouts
and brass sample port plug clears panel matching
hole.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

16
Figure 7: Purpose of Tappings and Bosses
TABLE 3: PURPOSE OF TAPPINGS & BOSSES
Tapping Location Size, NPT Boss Location Thread Size UNC Steam Boiler
Less Heater With Heater
A ¼" - 18 Pressure Gauge
B ¼" - 18 Pressure Limit
C ¾" - 14 Probe LWCO - Std. Plugged
(Float LWCO)
D ½" - 14
Water Gauge Glass (Probe LWCO) Water
Gauge Glass, Pressuretrol & LWCO (Float
LWCO)
E 2" - 11½" Supply (Front & Rear Tappings)
F ¾" - 14 Safety Valve
G 1½" - 11½ Condensate Return
H 1¼" - 11½ Optional Front Return
J 1½" - 11½ Surface Blowoff (Plugged)
K 1" - 11½ Indirect Water Heater Supply
L ½" - 14 Indirect Water Heater Limit
M (4 pcs) 5/16" - 18 Jacket Front Panel, Burner Swing Door
Mounting Bracket
N (2 pcs) 3/8" - 16 Burner Swing Door
P (10 pcs) 5/16" - 18 Jacket Rear Panel, Smoke Box Collar,
Cleanout Covers
Q ¼" - 18 Smokebox Pressure Tapping
R ½"-14
L4006
Operating
Control
Plugged
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

17
7. Secure panel bottom to studs with acorn nuts hand
tight.
8. Align upper panel attachment holes with smokebox
upper attachment bosses and install 5/16”-18 x ½”
Phillips pan head machine screws hand tight.
9. Securely tighten rear jacket panel mounting
hardware.
10. Locate/remove four #8 x ½” shoulder sheet metal
screws from Hardware Bag, then, install them into
rear panel ange holes.
H. FLUE CLEANOUT COVERS AND SMOKEBOX
COLLAR INSTALLATION.
1. Remove two cast iron Cleanout Covers, cast iron
Smokebox Collar and the tube of hi-temperature
silicon adhesive sealant from Part Carton. See also
“Repair Parts” Section, “Bare Boiler Assembly”
illustration for part identication.
2. Check the rope gasket factory attached to the covers.
Repair or replace, if the rope is damaged, or, there is
a gap between the rope ends.
3. Locate/remove four 5/16”-18 – 7/8” hex head cap
screws from Hardware Bag.
4. Apply a drop of supplied Anti-seize (pouch provided
in Part Carton) to each of four (4) 5/16”-18 x 7/8”
hex head cap screws for rust protection and to
facilitate easy removal for future service.
5. Position left Cleanout Cover over rear section
cleanout opening, align section boss holes with
Cleanout Cover holes, install both 5/16”-18 – 7/8”
hex head cap screws hand tight, then, alternately
tighten them with open end or socket wrench.
6. Repeat above steps with right Cleanout Cover.
7. Apply the adhesive sealant to the underside of the
collar, all around, at the inside corner of the collar
outer ring. Insure adhesive bead is complete all
around and without gaps.
8. Place the collar over smokebox tongue and align
collar integral mounting ear slots with smokebox
bosses.
9. Thread-in both 5/16”-18 – 7/8” hex head cap screws
hand tight, then, alternately tighten them with open
end or socket wrench.
I. INSULATION WRAPPER AND BURNER
POWER OUTLET RECEPTACLE WITH
HARNESS INSTALLATION.
1. Insulation Wrapper is vacuum packed/sealed in
plastic bag at the factory.
2. Carefully cut the plastic bag and remove Insulation
Wrapper. The wrapper will expand upon removal.
3. Unfold Insulation Wrapper, position it over section
assembly centered left to right and align two
wrapper upper holes with 2" NPT pipe tappings in
front and rear section top.
4. Insure wrapper ts snugly around rear section
tankless heater collar/ mounting ange (if boiler
is equipped with tankless heater) and trim the
insulation at tankless heater cutout. Do not trim off
insulation on boilers having non-heater rear section.
5. Tack Insulation Wrapper bottom ends under section
assembly, between front and rear section legs.
6. Locate and remove Burner Power Outlet Receptacle
with factory attached Burner Harness from Control
Carton.
7. Feed Molex end of Burner Harness thru front jacket
panel right side outlet receptacle cutout. Insure
that the receptacle middle prong opening is facing
down. Snap the receptacle into front jacket panel.
Temporarily, stuff Molex end of Burner Harness
between front panel insulation and insulation
wrapper near boiler top.
J. SIDE AND TOP JACKET PANEL
INSTALLATION.
1. Pick up Left Side Jacket Panel from Jacket Carton.
See also “Repair Parts” Section, “Jacket Assembly”
illustration for part identication.
2. Place Left Side Jacket Panel over four #8 x ½”
shoulder sheet metal screws, earlier installed at
Front and Rear Jacket Panel side anges, so teardrop
cutouts in the side panel inside anges engage all
four screws simultaneously.
3. Slide the panel downwards to lock all screws
securely.
4. Pick up Right Side Jacket Panel from Jacket Carton.
See also “Repair Parts” Section, “Jacket Assembly”
illustration for part identication.
5. Pick up Molex end of Burner Harness stuffed
between front panel insulation and insulation
wrapper and feed it thru Right Side Jacket Panel
front cutout, letting the harness connector to hang
over the cutout edge temporarily.
6. Place Right Side Jacket Panel, clearing rear section
tankless heater collar/ mounting ange, over four
#8 x ½” shoulder sheet metal screws, previously
installed at Front and Rear Jacket Panel side anges,
so teardrop cutouts in the side panel inside anges
engage all four screws simultaneously.
7. Slide the panel downwards to lock all screws
securely.
8. Pick up Top Jacket Panel from Jacket Carton.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

18
9. Place the panel between side panels upper inside
anges and slide it forward, until top panel front
ange U-bend locks over front panel top ange, and,
top panel rear ange is positioned over rear jacket
panel.
10. Locate/remove two #8 x ½” sheet metal screws from
Hardware Bag.
11. Install both screws into top panel rear ange to
secure the top panel to rear jacket panel.
K. EXTERNAL ELECTRICAL ENCLOSURE
MOUNTING.
1. Remove two #8 x ½” shoulder sheet metal screws
and one #8 x ½” sheet metal screw from Hardware
Bag.
2. Install both #8 x ½” shoulder sheet metal screws
into Right Side Jacket Panel, at two upper corners of
the panel front cutout.
3. Locate and remove External Electrical Enclosure
assembly from Control Carton.
4. Remove the enclosure cover and set aside.
5. Pick Molex connector end of Burner Harness and
feed it inside the enclosure, thru bushed hole at
enclosure lower left corner, next to transformer/
relay.
6. Place the enclosure over installed shoulder sheet
metal screws, so teardrop cutouts in the enclosure
base engage both screws simultaneously, then, slide
the enclosure downwards to lock it in place.
7. Install #8 x ½” sheet metal screw thru enclosure
base lower hole, located to the right of transformer/
relay, into right side panel to secure the enclosure.
8. Plug-in burner harness Molex connector into
dedicated burner harness receptacle inside the
enclosure (lower left off transformer/relay). See “
Control Plug-In Diagram” label attached to inside of
the enclosure cover for details.
9. Do not install the enclosure cover yet; proceed to
control installation.
L. TRIM AND CONTROLS INSTALLATION.
Pressure Limit Installation.
1. Locate and remove L404F Pressure Limit with
factory attached harness from Control Carton.
2. Locate and remove 1/4" NPT x 1-7/8" x 4 x 90°
syphon enclosed in Part Carton.
3. Review and locate pressure limit tapping on front
section. See Table 3 “ Purpose of Tappings &
Bosses” and Figure 7.
4. Thread 1-7/8" lg. syphon-threaded short end into
the bottom of Pressure Limit with factory attached
Figure 8: Pressure Limit Installation
harness. Do not tighten the syphon by holding the
limit case; apply a wrench to the brass hex below
the case.
5. Thread ¼" NPT x 4" lg. syphon-threaded long end
into pressure limit tapping on front section. See
Figure 8 "Pressure Limit Installation.
6. L404F pressure limit does not require leveling. The
pressure limit nal orientation must be parallel to
boiler front, having the harness on the right side.
7. Pick-up the pressure limit harness Molex end and
feed it into the enclosure, thru top ange rear left
7/8” hole; then, snap-in harness BX connector into
the hole, and, plug Molex connector into dedicated
pressure limit receptacle inside the enclosure (upper
left off transformer/relay). See “ Control Plug-In
Diagram” label attached to inside of the enclosure
cover for details.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)
M. PROBE LWCO (HYDROLEVEL CG450,
OR, MCDONNELL-MILLER PS801-120)
INSTALLATION.
1. Remove either Hydrolevel CG450 LWCO with
factory attached harness and Hydrolevel probe
#EL1214, or, McDonnell-Miller PS801-120 with
factory attached harness and #153875 probe from
Control Carton.
2. Install the probe into the appropriate front section
tapping. See Figure 7 “Purpose of Tappings &
Bosses”.
3. Slip LWCO with factory attached harness over the
probe and clamp in place. Note that CG450 LWCO
will be positioned right side up, with diagnostic
LED(s) on the top ange, while PS801 LWCO
will be positioned upside down, with diagnostic
LED(s) on the bottom ange. Connect the wire(s)
between the probe and control per manufacturer’s
instructions.

19
Figure 9: Float-Type LWCO and Pressure Limit Installation
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)

20
4. Pick-up the LWCO harness Molex end and feed it
into the enclosure, thru external electrical enclosure
top ange front left 7/8” hole; then, snap-in harness
BX connector into the hole, and, plug-in Molex
connector into dedicated LWCO receptacle inside
the enclosure (middle left off transformer/relay). See
“ Control Plug-In Diagram” label attached to inside
of the enclosure cover for details.
N. PRESSURE GAUGE AND GAUGE GLASS
INSTALLATION.
1. Remove the 6” water gauge glass set from Part
Carton.
2. Install the gauge glass using the two ½” NPT
tappings to the right of the probe LWCO. See Figure
7 “Purpose of Tappings & Bosses”.
3. Thread the pressure gauge into 1/4” NPT tapping of
the front section. See Figure 7 “Purpose of Tappings
& Bosses”. Tighten with wrench applied to the
square shank of the gauge.
CAUTION
Do not apply pressure to gauge case, as this may
result in inaccurate readings.
O. FLOAT LWCO (MCDONNELL-MILLER #67),
AND GAUGE GLASS INSTALLATION.
1. Pre-assemble oat-type LWCO per Figure 9 "Float-
Type LWCO and Gauge Glass Installation".
2. Install two ½” NPT x 2½" long Sch 40 brass nipples,
supplied loose inside Control Carton (disregard two
½" NPT x 1½" long brass nipples provided with
#67 LWCO package) and ½" NPT brass unions into
upper and lower front section tappings. See Table 3
"Purpose of Tappings & Bosses" and Figure 7.
3. Install water gauge glass on low water cut-off
assembly tee ttings.
4. Do not remove ¼” NPT plug factory installed on top
of #67 LWCO.
5. Insure that 3/8" NPT plug (provided within #67
LWCO package) is installed at bottom of #67
LWCO.
6. Remove #67 LWCO J-box cover.
7. Screw LWCO to External Wiring Enclosure wiring
harness (end with fork and female disconnect
terminals) connector into low water cut-off J-box
top tting, and attach wires to the terminals per
LWCO wiring detail shown in Figure 9 "Float-Type
LWCO and Gauge Glass Installation".
8. Re-install #67 LWCO J-box cover.
9. Pick-up the LWCO harness Molex end and feed it
into the enclosure, thru external electrical enclosure
top ange front left 7/8” hole; then, snap-in harness
BX connector into the hole, and, plug-in Molex
connector into dedicated LWCO receptacle inside
the enclosure (middle left off transformer/relay). See
“ Control Plug-In Diagram” label attached to inside
of the enclosure cover for details.
10. Pick-up the pressure limit harness Molex end
and feed it into the enclosure, thru External
Electrical Enclosure top ange rear left 7/8” hole;
then, snap-in harness BX connector into the hole,
and, plug-in Molex connector into dedicated pressure
limit receptacle inside the enclosure (upper left off
transformer/relay). See “ Control Plug-In Diagram”
label attached to inside of the enclosure cover for
details.
P. AQUASTAT CONTROLLER INSTALLATION
(BOILERS WITH TANKLESS HEATER ONLY).
1. On boilers with tankless heater, install the L4006A
aquastat controller well (found in Part Carton) into
½” NPT tapping in tankless heater plate.
2. Remove the L4006A aquastat controller with factory
attached harness from Control Carton.
3. Slip the bulb of the aquastat controller into the well
and secure the controller in place with the set screw.
WARNING
Aquastat bulb must be fully inserted into the
well.
4. Feed the L4006A aquastat controller harness end
thru external electrical enclosure top ange middle
right bushed hole. See “ Control Plug-In Diagram”
label attached to inside of the enclosure cover for
details.
5. See Figures 19, 20 and 21 (whichever applicable)
for tankless heater aquastat connection details.
6. Using needle nose pliers form hook on harness each
stripped end and wrap hooks around screws under
terminals "R" and "G" of the R8285C Transformer-
Relay; then, tighten screws securely.
Q. SAFETY VALVE AND DRAIN VALVE
INSTALLATION.
1. Remove safety valve and related piping (3/4”
NPT x 3” lg. black nipple, 3/4” NPT x 8” lg. black
nipple, ¾” NPT 90° black elbow and ¾” NPT black
coupling) from Part Carton.
2. Thread 3/4" NPT x 3” lg. black nipple into rear
section safety valve tapping, install ¾” NPT 90°
black elbow facing upward, then, thread 3/4" NPT
x 8” lg. black nipple into the elbow, and, install ¾”
NPT black coupling onto nipple end.
SECTION II: UNIT-PAK BOILER ASSEMBLY (continued)