Bradford White MII50A-SF User manual

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Manual 238-47174-00B
SERVICE
MANUAL
Troubleshooting Guide
and Instructions for Service
(To be performed ONLY by
qualified service providers)
Models Covered
by This Manual:
MII50(A)-*-**-(SF,CF,SCF)-***
MII80(A)-*-**-(SF,CF,SCF)-***
MII120(A)-*-**-(SF,CF,SCF)-***
*Denotes kW Rating
**Denotes Warranty Years
***Denotes Wiring Code
IMMERSION AND SURFACE MOUNTED
THERMOSTAT MODELS
COMMERCIAL ELECTRIC ENERGY SAVER
WATER HEATER
MII SERIES
®

Table of Contents Page Service Procedure
Introduction ………………………………………………………………………. 2 - - -
Tools……………………………………………………………………………… 2 - - -
General Information ……………………………………………………………… 3 - - -
Sequence of Operation …………………………………………………………… 10 - - -
Troubleshooting …………………………………………………………………. 13 - - -
Heating Element Testing …………….................................................................... 15 MCE-I
Line Voltage Testing………………...…………………………………………… 16 MCE-II
Fuse Testing…........................................................................................................ 17 MCE-III
High Limit (ECO) Testing (Surface Mounted Thermostats)……………………. 18 MCE-IV
High Limit (ECO) Testing (Surface Mounted Thermostats at 600V)……………. 19 MCE-V
High Limit (ECO) Testing (Contactor Models)…………………………………. 20 MCE-VI
Thermostat Operation Testing (Surface Mounted Thermostats).............................. 21 MCE-VII
Thermostat Operation Testing (Surface Mounted Thermostats at 600V)………… 22 MCE-VIII
Thermostat Operation Testing (Contactor Models)..................................................23 MCE-IX
Contactor Operation Testing……………………………………………………… 24 MCE-X
Thermostat Removal and Replacement (Surface Mounted Thermostats)………… 26 MCE-XI
Thermostat Removal and Replacement (Contactor Models)………………………27 MCE-XII
ECO Removal and Replacement (Contactor Models)……………………………..28 MCE-XIII
ECO Removal and Replacement (Surface Mounted Thermostats at 600V)……….29 MCE-XIV
Heating Element Removal and Replacement …………………………………….. 30 MCE-XV
Anode Inspection and Replacement ……………………………………………… 31 MCE-XVI
Generic Parts List ………………………………………………………………… 32 - - -
Glossary of Terms……………………………………………………………….... 33 - - -
Page 2
This service manual is designed to aid service and maintenance professionals on the function, proper diagnosis and repair of
Bradford White Commercial Electric Water Heaters.
The text and illustrations in this manual provide step by step instructions to facilitate proper operation and troubleshooting
procedures. Contact the Bradford White Technical Support Group immediately if diagnosis can not be made using the
methods described in this service manual.
Introduction
MII Series Commercial Electric
Water Heaters
Tools
- Multi Meter. - Phillips Head Screw Driver.
- 1-½” Deep Well Socket. - Common Screw driver.
- 1-1/16" Deep Well Socket. - Thermometer.
- ¼" Nut Driver. - Drain Hose.
- Other Hand Tools: Pipe Wrench, Channel Locks, Pliers (common & needle nose), Wire cutters, Wire Strippers,
Allen Wrench Set, Flash Light.
2

GENERAL INFORMATION
Bradford White MII Series Commercial Electric water heaters can be manufactured with a choice between two
different types of thermostat control options as follows:
Surface Mounted Thermostats.
Immersion Thermostat (contactor models).
The model number is coded to identify the specific thermostat control system used for a particular unit. Below is
typical model number and coded definitions:
MII50 12 3 SF 018
Wiring Code
C-Contactor (Immersion Thermostat)
CF-Contactor w/Fuse (Immersion Thermostat)
S-Surface Thermostat
SF-Surface Thermostat w/Fuse
SC-Surface Thermostat (w/Contactors)
SCF-Surface Thermostat w/Fuse (w/Contactors)
Warranty
kW Rating
Tank
The wiring code at the end of the model number is used at the factory to facilitate proper construction based on the
electrical characteristics such as voltage, phase, kW rating and amp draw. In the field this information is determined
from the heaters rating plate located on the front of the water heater.
BRADFORD WHITE CORPORATION
200 LAFAYETTE ST. MIDDLEVILLE MI 49333
Model No: MII50123SF018
Serial No: ZB2564812
Cap. 50(gal.)/189.3(liters)
Press: Test 300(psi), Working 150(psi)
Volts 240 Max Temp 180°
Phase Three Amps 29
kW Each 4 Total kW 12 3 Elements
Wattage Rating Based Upon 60 Hz
Page 3
Typical Rating Plate
Located On Front Of Water Heater
Model Number
Electrical Characteristics
3

Page 4
GENERAL INFORMATION
Upper
Control Box
Lower
Control Box
Ground Lug
Terminal Block
Fuse Block(s)
Contactor(s)
High Limit (ECO) Control
Immersion Thermostat
Control
High Limit (ECO)
Direct Immersion Bulb
Thermostat
Direct Immersion Bulb
Heating Elements
Contactor Models
General Controls Layout
Surface Mounted Thermostat Models
General Controls Layout
Upper
Control Box
Lower
Control Box
Ground Lug
Terminal Block
Fuse Block(s)
Heating Elements
Surface Mounted Thermostats
With ECO
4

Page 5
GENERAL INFORMATION
Upper
Control Box
Lower
Control Box
Ground Lug
Terminal Block
Contactor(s)
Surface Thermostats
Heating Elements
High Limit (ECO) Control
600V Surface Thermostat (w/Contactors) Models
General Controls Layout
5

GENERAL INFORMATION
Page 6
Surface Mounted Thermostats
Manual
ECO (high limit)
Reset button
Temperature
control Dial
Surface Mount
Combination Thermostat/
ECO (high limit)
89T Series
Surface mounted thermostats are mounted into a bracket above each heating element. The bracket holds the
thermostat against the side of the tank responding to tank surface temperatures to sense a call for heat, set point
temperature and high limit (ECO) activation. As each element has a dedicated thermostat (for all models excluding
600V), it is possible to sequence the elements by varying the settings on the thermostats.
The thermostat will complete control circuit
voltage upon a call for heat. Likewise, the control
will interrupt control circuit voltage when the water
temperature is sufficient to satisfy the adjustable
temperature limit of control.
Immersion Style Thermostat Control for
Contactor Models
Direct
Immersion
bulb
The high limit (ECO) control will interrupt control circuit voltage
causing the heater to shut down when the high temperature limit of
the control is reached (196°F±4°F). Once the cause for over
heated water has been determined, The control must be manually
reset to restore normal operation.
Immersion Style High Limit (ECO) Control for
Contactor Models
Direct
Immersion
bulb
Manual Reset
Buttons
6

GENERAL INFORMATION
Page 7
Surface Mounted Thermostats (w/Contactors) for
600V Models
600V models use contactors to deliver line voltage to the heating elements. However, rather than the immersion type
high limit and thermostat devices, surface mounted thermostats are used to operate the control circuit of the water
heater.
Temperature
control Dial
Surface Mounted
Thermostat
59T Series
Manual Reset
Button
Surface Mounted
ECO (High Limit)
7

GENERAL INFORMATION
Contactor
1-½” Hex
Screw-in Flange
Terminal Block
Screw
Terminal Block
Zinc Plated Copper or
Incoloy Sheath
Element Rating Ink Stamped
on side of Terminal Block.
Direct Immersion “Screw-in” Type Heating Element
0642
4500W 240V
RC02404524
Page 8
Contactoroperation is achieved by energizing an operating coil in response toa call forheat fromthe immersion
thermostat.Upon a call forheat,one or morecontactorswill energizeall heating elementssimultaneously.The
operating coilsare voltage specific,When contactorreplacementis required be suretoorder the proper operating coil
baseon the voltage rating found on the rating plate located on thefront of thewater heater.
Terminalconnectionsto the
fuseblock and/or terminalblock
Terminal connections to the
heating elements
Terminal connections of
contactor operating coil.
8

GENERAL INFORMATION
Watts
Volts x 1.732 Watts = Amps x Volts Volts
Watts
2
Commonly Used Formulas
240V 1Ph
Ungrounded
Ungrounded
Grounding
BLACK
RED
GREEN
240
120
Common Service Wire
Configurations
Page 9
120
(balanced 3 phase)
Amps =
Watts
Volts
(Single phase)
Amps = Ohms =
120
ABCNeutral
RED BLACK RED
120
120 208
208 208
208 3Ph
120
ABCNeutral
RED BLACK RED
120
120 240
240 240
240 3Ph
277
ABCNeutral
RED BLACK RED
277
277 480
480 480
480 3Ph/277 1Ph
Full Load Current Amps
208 Volt
1 Ph 3 Ph
6
kW
9
12
13.5
15
18
24
27
30
36
45
54
28.8 16.6
43.2 25.0
57.6 33.3
64.9 37.5
72.1 41.6
86.5 50.0
115.4 66.7
129.8 75.0
144.2 83.3
173.0 100.0
216.3 125.0
259.6 150.0
240 Volt 277 Volt 380 Volt 415 Volt 480 Volt 600 Volt
25.0 14.4
37.2 21.6
50.0 28.9
56.2 32.5
62.5 36.1
75.0 43.4
100.0 57.8
112.5 65.0
125.0 72.2
150.0 86.7
187.5 108.3
225.0 130.0
12.5 7.2
18.7 10.8
25.0 14.4
28.1 16.2
31.2 18.0
37.5 21.6
50.0 28.9
56.2 32.5
62.5 36.1
75.0 43.3
93.7 54.1
112.5 65.0
1 Ph
21.6
32.4
43.3
48.7
54.1
64.0
86.6
97.4
108.3
129.9
162.4
194.9
3 Ph
8.3
12.5
16.7
18.8
20.9
25.0
33.4
37.5
41.7
50.1
62.6
75.1
3 Ph
9.1
13.6
18.2
20.5
22.7
27.3
36.4
41.0
45.6
54.7
68.4
82.0
3 Ph
5.8
8.7
11.5
13.0
14.4
17.3
23.1
26.0
28.9
34.6
43.3
52.0
1 Ph 3 Ph 1 Ph 3 Ph
9

SEQUENCE OF OPERATION
MII Series Commercial Electric Water Heaters can use either immersion thermostat (contactor models) or
surface mounted thermostats. Sequence of operation for each configuration is explained below. It would be impractical
to show all wire diagrams applicable to both configurations. A “typical wiring diagram” is illustrated to aid in
understanding the principles of the operating sequence.
Immersion Thermostat (Contactor Models): Configured to use a single immersion thermostat to control one or more
contactors to energize or de-energize all elements simultaneously. In addition, a separate high limit (ECO) control with
manual reset is wired in series with the thermostat. Both controls use a direct immersion bulb inserted into the tank to
sense water temperature. Immersion thermostat and high limit control are mounted to provide temperature adjustment
and manual reset access from the exterior of the unit.
Surface Mounted Thermostats: Surface mounted thermostats are mounted inside the lower control box, in a bracket
above each heating element. The bracket holds the thermostat against the side of the tank responding to tank surface
temperatures to sense a call for heat, set point temperature and high limit (ECO) activation. As each element is controlled
by a dedicated thermostat, it is possible to sequence the elements by varying the settings on the thermostat. However,
600V models w/ surface mounted thermostats operate contactors in the same manner as an immersion thermostat
model, only using surface thermostats to sense the call for heat.
Sequence of operation for each system is explained below.
Sequence of Operation:
Immersion Thermostat (Contactor Models).
Line voltage is applied across terminals of fuse block
or a terminal block. Line voltage continues down and
connects to terminals L1, L2 & L3 of one or more
contactors.
A) Contactor is open (no call for heat), so there is no
voltage across terminal T1, T2 & T3
of contactor.
B) The contactor is controlled by the control circuit
consisting of the immersion thermostat,
ECO (hi limit) and contactor coil.
Page 10
1
2
OR Terminal Block
Fuse Block
Line Voltage
Contactor
Contactor
Coil ECO
(High Limit)
T’stat
When the thermostat calls for heat, contacts close
inside the thermostat completing the circuit through
the ECO and energizing the contactor coil.
The system has two distinct circuits.
1. Power circuit (shown solid line).
2. Control Circuit (shown dotted line).
The energized contactor coil causes the contactor to
close energizing the elements from terminals T1, T2
& T3 of the contactor.
3
When the temperature setting of the thermostat is
reached, the contacts in the thermostat open. This
interrupts current flow through the control circuit de-
energizing the contactor coil.
4
The de-energized contactor coil causes the contactor
to open, interrupting current flow through the
elements. The heater is now in stand-by waiting for
the next call for heat.
5
Heating Elements
10

SEQUENCE OF OPERATION
Sequence of Operation:
Surface Mounted Thermostats.
OR Terminal Block
Fuse Block
Line Voltage
Heating Element
Surface Mounted
Thermostat
Line voltage is applied across terminals of fuse block or a
terminal block. Line voltage continues down and connects
to surface mounted thermostats at terminals L1 & L3.
1
1
ECO (high limit) in
thermostat is closed, so
there is line voltage present
at terminal L4 of thermostats
and to one side of each
element.
2ECO Closed
Power to one
side of element
2
3
Water in tank is cold, so
all thermostats are
closed at terminal T2
(calling For heat). This
completes the circuit and
allows current to flow
through heating elements.
3Thermostat closed
at terminal T2
4
As each thermostat is
satisfied, it opens at
terminal T2 interrupting
current flow through the
respective element. The
system is now in stand-by
mode, waiting for the next
call for heat.
4
Thermostat open
at terminal T2
Page 11
11

SEQUENCE OF OPERATION
Sequence of Operation:
600V Surface Mounted Thermostats (w/Contactors).
Line voltage is applied across terminals of fuse block
or a terminal block. Line voltage continues down and
connects to terminals L1, L2 & L3 of one or more
contactors.
A) Contactor is open (no call for heat), so there is no
voltage across terminal T1, T2 & T3
of contactor.
B) The contactor is controlled by the control circuit
consisting of the surface mounted thermostat,
ECO (hi limit) and contactor coil.
Page 12
1
2
Contactor
Fuse Block
Line Voltage
When the thermostat calls for heat, contacts close
inside the thermostat completing the circuit through
the ECO and energizing the contactor coil.
The system has two distinct circuits.
1. Power circuit - Line Voltage (600V)
2. Control Circuit - 120V
The energized contactor coil causes the contactor to
close, energizing the elements from terminals T1, T2
& T3 of the contactor.
3
When the temperature setting of the thermostat is
reached, the contacts in the thermostat open. This
interrupts current flow through the control circuit de-
energizing the contactor coil.
4
The de-energized contactor coil causes the contactor
to open, interrupting current flow through the
elements. The heater is now in stand-by waiting for
the next call for heat.
5
Heating Elements
High Limit
59T
Transformer
60VA
59T
Notice in the wiring diagram at right that each row of
elements is equipped with a surface mounted
thermostat on the highest element in the row. These
thermostats are individually wired in series to the
contactor whose line voltage corresponds to the same
row of elements. Each thermostat and contactor
combination are wired to the high limit (ECO) device
in parallel. This allows for each row of elements to be
powered “ON” independent of the other element rows.
However, the high limit (ECO) is wired in series so
that voltage can be interrupted to the entire control
circuit if the ECO senses that the tank water has
become overheated.
6
6 Element Configuration Shown
(9 Elements Possible)
12

TROUBLESHOOTING
Most common cause for improper electric water heater operation can be linked to heating element
failure.
When troubleshooting an electric water heater with the incidence of “No Hot Water” or “Insufficient Amount of Hot
Water” It is always a good idea to check the heating elements first following the procedure on page 15.
Common Heating Element Failures Are:
1. Dry Firing. Elements may be partially submerged in water or most likely, completely exposed with no water
in the tank at all. In open air, an energized element (Dry Fired) will become completely inoperable within
seconds. In some cases sediment or lime build up around an element can eventually cause an air pocket,
resulting in a dry fired element. When element replacement is required, be sure tank is full of water prior to
energizing the water heater.
2. Grounded Element. In most cases, an element with a short circuit to ground will cause the circuit breaker in
the service panel to open or shut off. In some cases there may not be enough current draw for the circuit
breaker to open. This will allow the heating element to be in continuous operation resulting in over heated
water, limited only by the ECO or Energy Cut Off located in the thermostat circuit. Repeated actuation of the
ECO usually is the result of a grounded heating element.
3. Sediment build up. Slow hot water recovery can usually be traced back to sediment or lime build up around
heating element. Sediment build up can also over time cause a dry fired element.
If a heating element is found to be inoperative, it must be replaced. Follow service procedure MCE-XV on page 30.
The illustration below shows a common “Screw-In” type heating element identifying certain features commonly referred
to throughout this manual.
1-½ Hex
Screw-in Flange
Terminal Block
Screw
Terminal Block Zinc Plated Copper or
Incoloy Sheath
Element Rating Ink Stamped
on side of Terminal Block.
Typical Direct Immersion “Screw-In”
Type Heating Element
Page 13
0642
4500W 240V
RC02404524
13

SYMPTOM PROBABLE CAUSE CORRECTIVE ACTION
No Hot Water
1. No power to heater.
2. Blown water heater fuses.
3. Loose wire connections.
4. Inoperative heating elements.
5. Inoperative thermostat(s).
6. Open ECO.
7. Inoperative contactor(s).
1. Inoperative heating element.
2. Sediment or lime build up on element(s).
3. Thermostat(s) set to low.
4. Inoperative thermostat(s).
5. Inoperative contactor(s).
6. Loose wire connection.
7. High demand period.
8. Undersized heater.
9. Very cold inlet water to heater.
10. Plumbing connections reversed.
Not Enough Hot
Water or
Continues
Operation
Slow Hot Water
Recovery
1. Sediment or lime build up on element(s).
2. Loose wire connections.
3. Inoperative thermostat(s).
4. Inoperative contactor(s).
5. Derated heating element installed.
Over Heated
Water
1. Surface thermostat(s) not flush with tank.
2. Grounded heating element(s).
3. Thermostat set to high.
4. Inoperative thermostat(s).
5. Inoperative ECO.
1. Check circuit breakers at service panel.
2. Check water heater fuses.
3. Check all wire connections.
4. Check heating element(s).
5. Check thermostat(s) operation.
6. Reset (check) ECO.
7. Check contactor operation.
1. Check heating element(s).
2. Clean or replace heating element(s)
3. Increase thermostat setting.
4. Check thermostat(s).
5. Check contactor operation.
6. Check all wire connection.
7. Reduce demand.
8. Replace with larger heater.
9. Temper water to heater.
10. Correct plumbing connections.
1. Clean or replace heating elements.
2. Check all wire connections.
3. Check thermostat(s).
4. Check contactor operation.
5. Verify element voltage and wattage rating.
1. Check surface thermostat(s) mounting.
2. Check heating element(s).
3. Adjust thermostat(s) to desired setting.
4. Check thermostat(s).
5. Check ECO.
SERVICE
PROCEDURE
2. MCE-III, Page 17
4. MCE-I, Page 15.
5. MCE-VII-IX, Page 21-23.
6. MCE-IV-VI, Page 18-20.
7. MCE-X, Page 24,25
1. MCE-I, Page 15.
2. MCE-XV, Page 30.
4. MCE-VII-IX, Page 21-23.
5. MCE-X, Page 24,25
1. MCE-XV, Page 30.
3. MCE-VII-IX, Page 21-23.
4. MCE-X, Page 24-25
5. See page 8.
1. MCE-XI, Page 26.
2. MCE-I, Page 15.
4. MCE-VII-IX, Page 21-23.
5. MCE-IV-VI, Page 18-20.
Page 14
Noisy (singing or
hissing) Elements
1. Lime formation on elements.
2. High or low line voltage.
1. Clean or replace heating elements.
2. Verify line voltage to heater.
1. MCE-XV, Page 30.
2. MCE-II, Page 16.
TROUBLESHOOTING
WARNING
High voltage exposure. Use caution when
making voltage checks to avoid hazard to
life or property.
Noisy Contactor
1. Low line voltage.
2. Debris between contactor plates.
3. Incorrect or defective operating coil.
4. Loose wire connections.
1. Verify line voltage to heater
2. Replace contactor.
3. Replace contactor.
4. Check wire connections.
1. MCE-II, Page 16
Quick Step Plan to Hot Water
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Check all wire connections to insure they are snug
and corrosion free.
3. Reset high limit (ECO) (page 18-20).
4. Check for inoperative heating element (page 15).
5. Check line voltage (pg 16), and internal fuses (page 17).
6. Refer to table below if items 1 through 5 above do not correct problem.
14

SERVICE PROCEDURE MCE-I
Heating Element Testing
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Remove access cover from lower control box.
Remove insulation from inside of control box.
3. Disconnect wires from heating element.
4. Set multi-meter to “ohms” setting.
5. Touch probes of multi-meter to screw
terminals of heating element
(see illustration 1).
6. Reading should be 12.8 ohms (±6%) for a 240
volt, 4500 watt element, see table below for other elements.
A reading outside the range using the formula
above (±6%), indicates a bad element and the
element must be replaced.
Test for Open or Burned Out Element. DANGER
High voltage exposure. To avoid hazard to
Life or property, be sure power is turned OFF
to water heater while performing this
procedure.
Test For Grounded Heating Element
(damaged heating element with short circuit to ground).
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Remove access cover from lower control box.
Remove insulation from inside of control box.
3. Disconnect wires from heating element.
4. Set multi-meter to “ohms” setting.
5. Touch one probe of multi-meter to either screw
terminal of heating element and the other on
the element flange (see illustration 2). There
should be no reading on the ohm meter. Any
reading indicates a grounded element and the
element must be replaced. Repeat this step for
the other screw terminal.
Ohms = Volts2
Watts
Element Screw Terminals
Element
Screw Terminal
Element Flange
Illustration 1
Illustration 2
Page 15
NOTE
Disconnect
element
Wires
NOTE
Disconnect
element
Wires
Ohms of electrical Resistance
For commonly Used Elements
Voltage Rating of Element
Element
Wattage 208 240 480
2000 21.6 28.8 115.2
3000 14.4 19.2 76.8
4000 10.8 14.4 57.6
4500 9.6 12.8 51.2
5000 8.7 11.5 46.1
6000 7.2 9.6 38.4
15

SERVICE PROCEDURE MCE-II
Line Voltage Testing
Page 16
Line Voltage Testing
Illustration 3
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Open upper control panel door.
3. Determine connection point for line voltage
from service panel, terminal block or
fuse block
4. Set multi-meter to volts AC. Be sure to scale
meter for appropriate voltage.
5. Use caution and turn power “ON” to water heater.
6. Use caution and check voltage across top terminals
where service voltage connects to water heater.
(see illustration 3).
A) Rated voltage IS present, power to
the water heater is okay.
B) Rated voltage NOT present, Check
service panel.
Line voltage (single phase or three phase) will
connect to a terminal block or directly to a fuse block
located inside control panel.
Determine heaters voltage and phase by referring to the rating plate located on the front of the heater. Apply the
appropriate phase procedure below to determine if proper line voltage is present.
Single Phase Line Voltage Testing
Line voltage from
service panel
connected to Terminal block
of heater
Line voltage from
service panel
connected to Fuse block
of heater
OR
Check voltage across
top terminals.
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Open upper control panel door.
3. Determine connection point for line voltage
from service panel, terminal block or
fuse block
4. Set multi-meter to volts AC. Be sure to scale
meter for appropriate voltage.
5. Use caution and turn power “ON” to water heater.
6. Use caution and check voltage across top terminals
where service voltage connects to water heater.
(see illustration 4).
A) Rated voltage IS present, power to
the water heater is okay.
B) Rated voltage NOT present, Check
service panel.
Three Phase Line Voltage Testing
Line voltage from
service panel
connected to Terminal block
of heater
Line voltage from
service panel
connected to Fuse block
of heater
OR
Check voltage across
top terminals.
Illustration 4
DANGER
High voltage exposure. To avoid hazard to
life or property use extreme caution when
making voltage checks .
16

SERVICE PROCEDURE MCE-III
Fuse Testing
Fuse Testing
1. Turn “OFF” power to water heater.
2. Open upper control box to allow access
to fuse block.
3. Locate fuse block and remove fuses.
4. Set multi-meter to the “Ohms” setting.
5. Check continuity across fuse
(see illustration 5).
A) Continuity IS present, fuse is okay.
B) Continuity NOT present, Replace with new fuse
Illustration 5
Page 17
DANGER
High voltage exposure. To avoid hazard to Life
or property, be sure power is turned OFF to
water heater while performing this procedure.
17

SERVICE PROCEDURE MCE-IV
High Limit (ECO) Testing
Page 18
1. This procedure assumes line voltage and
fuses are in working order.
2. This procedure illustrates testing of just one
surface thermostat. Repeat this procedure for all
surface thermostats on the unit.
3. Turn power “OFF” to water heater.
4. Remove lower control box cover and remove insulation
from inside of control box.
5. Remove plastic cover from thermostat(s).
6. Turn power “ON” to water heater.
7. Check voltage across terminals L1 & L4 for all thermostats
(see illustration 6).
A) Rated Voltage IS present, ECO is okay.
B) Rated voltage NOT present, proceed to step 8.
8. Turn power “OFF” to water heater and firmly press ECO reset button on thermostat(s).
Turn power “ON” to water heater and recheck voltage across terminals L1 & L4 of thermostat(s).
A) Rated voltage IS present, the ECO has previously opened indicating the water in the tank, at
some point did overheat, Check the following:
1. Thermostat must be in full contact with tank.
2. Be sure heating element(s) is not shorted to ground (see page 15).
3. Proper thermostat operation (see page 21).
B) Rated voltage NOT present, water in tank may be over heated.
1. If water is overheated, turn “OFF” power to water heater and flow water through tank to cool below
set point of upper thermostat. Reset ECO and recheck voltage.
2. If water is cool, Replace thermostat(s).
High Limit Control (ECO) Testing for
Surface Thermostat models (not including 600V)
ECO reset
button
Illustration 6
DANGER
High voltage exposure. To avoid hazard to
life or property use extreme caution when
making voltage checks .
18

SERVICE PROCEDURE MCE-V
High Limit (ECO) Testing
Page 19
1. This procedure assumes line voltage, transformer,
fuses, and thermostat are in working order.
2. Turn power “OFF” to water heater.
3. Remove lower control box cover and remove insulation
from inside of control box.
4. Check for continuity across terminals 1 & 2.
(see illustration 7)
A) Continuity IS present, ECO is okay.
B) Continuity NOT present, proceed to step 5.
5. Verify power to the water heater is “OFF”, firmly press the ECO
reset button. Recheck continuity across terminals 1 & 2
(see illustration 7).
A) Continuity IS present, the ECO has previously opened indicating the water in the tank, at
some point did overheat, Check the following:
1. Thermostat must be in full contact with tank.
2. Be sure heating element(s) is not shorted to ground (see page 15).
3. Proper thermostat operation (see page 22).
B) Continuity NOT present, water in tank may be over heated.
1. If water is overheated, verify that power to water heater is “OFF”. Flow water through the tank to cool
below set point of upper thermostat. Reset ECO and recheck continuity.
2. If water is cool, Replace ECO (High Limit).
High Limit Control (ECO) Testing for
600V Surface Thermostat Models
ECO reset
button
Illustration 7
DANGER
High voltage exposure. To avoid hazard to
life or property use extreme caution when
making voltage checks .
19

SERVICE PROCEDURE MCE-VI
High Limit (ECO) Testing
Page 20
High Limit Control (ECO) Testing for
Contactor Models
1. Determine if Hi-Limit has actuated. This can be done by simply
depressing the reset buttons. If you hear and/or feel
a small click, the switch has actuated.
2. Use caution and turn power on to water heater and observe
heating cycle following the Hi-Limit Heating Cycle flow chart.
Switch Contacts:
Normally closed.
Open on rise @ 196°F ±4°F
Manual Reset.
DANGER
High voltage exposure. To avoid
hazard to Life or property, be sure
power is turned OFF to water heater
while performing this procedure.
NIs water temp
over 196°F
N
Observe heating cycle.
Does switch open?
Switch OK
Is water temp
over 196°F
Replace switch
N
Y
Y
1. STOP, DANGER! Turn power “OFF” to water heater.
2. Water temperature must be below 196°F ±4°F
3. Remove Hi-Limit switch from control panel. It is not necessary
to remove immersion bulb from tank at this time. See
general controls layout on page 4 for location.
4. Disconnect wire leads to Hi-Limit Control during this test.
5. Depress reset buttons to insure switch contacts are closed.
6. Set multi-meter to Ohms setting, Check continuity Thru circuit A & B as shown in the illustrations below.
- Continuity IS present, Switch is okay.
- Continuity NOT present, Replace switch.
High Limit Control Continuity Testing for
Contactor Models
High Limit Heating Cycle Flow Chart
NOTE
Disconnect
Wire Leads to Control
Circuit “A” Continuity Testing Circuit “B” Continuity Testing
Y
20