Mizudo Electric Mini-Tank Water Heater

1 Safety Information

1.1 Safety Definitions

⚠️ DANGER: Indicates an imminently hazardous situation which, if not avoided, will result in death or serious injury.

⚠️ WARNING: Indicates a hazardous situation that, if not avoided, could result in death or serious injury.

⚠️ CAUTION: Indicates a hazardous situation which, if not avoided, could result in property damage and minor or moderate injury.

? NOTICE: This symbol indicates important information where there is no risk to people or property.

1.2 Important Safety Instructions

⚠️ WARNING: When using electrical appliances, safety precautions to reduce the risk of fire, electric shock or injury to persons should be followed.

1. READ ALL INSTRUCTIONS BEFORE USING THIS WATER HEATER.
2. This water heater must be grounded. Connect only to properly grounded outlet.
3. Install or locate this water heater only in accordance with the provided installation instructions.
4. Use this water heater only for its intended use as described in this manual.
5. Do not use an extension cord set with this water heater. If no receptacle is available adjacent to the water heater, contact a qualified electrician to have one properly installed.
6. As with any appliance, close supervision is necessary when used by children.
7. Do not operate this water heater if it has a damaged cord or plug, if it is not working properly, or if it has been damaged or dropped.
8. This water heater should be serviced only by qualified service personnel. Contact nearest authorized service facility for examination, repair, or adjustment.
9. Do not use multi-outlet adaptors (i.e. power strips) with this water heater.
10. Failure to inspect the anode rod at least once a year could cause the tank to fail and leak. This condition is not covered under the manufacturer's warranty.
11. Any water heater should be installed in such a manner that if it should leak, the resulting flow of water will not cause damage to the area in which it is installed. National Plumbing codes require a drain pan for any water heater installation. Failure to install one is the sole responsibility of owner and/or installer. Reference UPC 2006 (Uniform Plumbing Code) Section 508.1, or IPC 2006 (International Plumbing Code) Section 504.7.

CAUTION: The installer should review the contents of this manual with the owner upon completion of installation, and the manual should be left with the owner and placed in a location close to the installation.

CAUTION: The manufacturer cannot be responsible for the damages caused by improper installation or by failure to follow instructions in this manual. Comply with the installation instructions before completing electric connection.

CAUTION: The thermostat comes preset from the factory to be closed by default. (Fig. 1).

California Proposition 65 Warning

WARNING: This product can expose you to lead, which is known to the state of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.P65warnings.ca.gov.

Dangers of Hydrogen Gas

DANGER: Hydrogen gas is produced in a hot water system served by this heater that has not been used for a long period of time (2 weeks or more). Hydrogen gas is extremely flammable. To reduce the risk of injury under these conditions, it is recommended that the hot water faucet be opened for several minutes at the kitchen sink before using any electrical appliance connected to the hot water system. When hydrogen is present, there will probably be an unusual sound such as air escaping through the pipe as the water begins to flow. There should be no smoking or open flame near the faucet at the time it is open.

2 Information about the product

2.1 Models overview

Diagram (Fig. 2) shows the following components:

• 1. Temperature & pressure relief valve, 3/4 NPT male
• 2. Cold water inlet (BLUE) 1/2 NPT male (MDES-ET25 and MDES-ET40) / Cold water inlet (BLUE) 3/4 NPT male (MDES-ET80 equipped with converter)
• 3. Temperature Adjustment Knob
• 4. Temperature & pressure relief valve discharge line to drain
• 5. 3/4 NPT female tapping for relief valve
• 6. Hot water outlet (RED) 1/2 NPT male (MDES-ET25 and MDES-ET40) / Hot water outlet (RED) 3/4 NPT male (MDES-ET80 equipped with converter)

2.2 Dimensions

Diagrams (Fig. 3 & 4) illustrate the dimensions. The table below provides specific measurements:

* Vertically installation only

2.3 Technical data

3 Installation instructions

3.1 Mounting the heater

Wall mounting

? NOTICE: Material damages! Use screws that are suitable for the wall material and the weight of the heater.

After determining the installation position, drill two holes with a spacing of 2.44 inches and a diameter of 0.394 inches horizontally. The hole depth should not be less than 2.76 inches. Insert two plastic expansion tubes and fix the mounting bracket with screws.

Before hanging, align the two hanging holes on the back of the unit with the hooks on the support bracket. Pull down firmly to secure.

CAUTION: The appliance must be hung securely to prevent personal injury and property damage from falling.

Floor mounting

The heater can sit on the floor.

3.2 Pipe connections

• Connect the cold water inlet pipe (blue ring) to the inlet tapping.
• Ensure an isolation valve is installed on the cold water supply.
• Connect the hot water outlet pipe (red ring) to the outlet tapping.

CAUTION: To reduce the risk of excessive pressures and temperatures:

• Install temperature and pressure protective equipment as required by local codes, but not less than a combination temperature and pressure relief valve certified by a nationally recognized testing laboratory (e.g., ANSI Z21.22).
• The supplied relief valve is marked with a maximum set pressure (150 psi).
• Install the Temperature and pressure relief valve in the designated opening.
• Orient the discharge tubing so it exits within 6 inches above or at any distance below the structural floor, and does not contact any live electrical part. The discharge opening must not be blocked or reduced in size.

? NOTICE: Wrap Teflon tape around the threaded opening of the pressure relief valve at least 15 times (approx. 120 cm) to prevent water leakage.

National Plumbing codes may require a drain pan. Failure to install one is the owner's/installer's responsibility. Reference UPC Section 508.1 or IPC Section 504.7.

3.3 Closed system thermal expansion

Periodic discharge of the temperature and pressure relief valve or element gasket failure can occur due to thermal expansion in a closed water supply system. This can happen if the water utility meter has a check valve, backflow preventer, or pressure reducing valve.

During heating, water expands, increasing pressure. The relief valve may discharge hot water, leading to energy loss and lime buildup.

To prevent this:

• Install a diaphragm-type expansion tank suitable for potable water on the cold water supply line (minimum 0.5 gallon).
• Contact your local water supplier or plumbing inspector for guidance on controlling this situation. Do not plug the temperature and pressure relief valve.

4 Use

4.1 Starting and testing

CAUTION: DO NOT supply power to water heater until filled with water.

To fill the heater:

• Open the supply valve to fill the heater with water.
• Open hot water tap(s) to purge air from the system. Close hot water tap once air is purged.
• Visually check for any leaks.

Turning heater on

For models without a switch:

• Plug in the power cord.
• If the indicator light does not come on, turn the control knob clockwise.

The light will turn on until the water reaches the set temperature and will turn on again if the temperature drops.

DANGER: If water pressure is high, the TP valve may relieve pressure during heating. Water temperature can exceed 145°F after pressure relief, potentially causing severe burns or death from scalds. Pay attention!

4.2 Temperature setting

The hot water temperature is adjusted by rotating knob M (Fig. 5) on the front cover. The temperature range is 55-145°F.

• Turn the knob clockwise to increase temperature.
• Turn the knob counter-clockwise to decrease temperature.

5 Maintenance

CAUTION: Do not attempt to repair this water heater yourself. Call a service person. Always turn off the power supply before servicing or draining.

? NOTICE: For most operations, the water must be drained. Disconnect the power cord and remove the front cover.

5.1 Removing the cover

• Remove the rubber seal covering the Phillips screw (Fig. 5 [S]) and unscrew it.
• The cover (Fig. 5 [C]) can be removed by rotating it slightly. When reassembling, reverse the process, ensuring the cover's tongue inserts into the slot.

5.2 Draining the heater

If installed with flexible hoses:

• Shut off the power supply.
• Turn the heater upside down over a sink to drain the water.

5.3 Inspecting the anode rod

If installed with flexible hoses:

The anode rod (Fig. 8 [N]) protects the tank from corrosion. It must be inspected annually for replacement. To access it, the heating element must be removed (see Section 5.4). The anode rod surface should be smooth. If pitted, bumpy, rusty, or missing, it must be replaced.

To access the anode rod:

• Remove the heating element (see Section 5.4).

5.4 Removing the heating element

• Take out the power cord L from the plastic part (Fig. 6).
• Use a cross screwdriver to unscrew the 3-in-1 cross screw J on the heating element terminals (red wire J, blue wire C) (Fig. 6).
• Remove wire nail I, press thermostat capillary G and thermal cut-out capillary H, and take them out of the blind tube opening (Fig. 6).
• Loosen the 5 nuts and spring washers on the heating element pressing plate A with a sleeve, and remove plate A (Fig. 6).
• Remove heating element B (Fig. 6).

Diagram (Fig. 6) shows components: A. Heating Element Pressing Plate, B. Heating Element, C. Wire, D. Live Wire, E. Null Wire, F. Return Pin, G. Thermostat Capillary, H. Thermal cut-out Capillary, I. Wire Nail, J. 3-in-1 Cross Screw, K. Ground Wire, L. Power Cord.

Diagram (Fig. 7) shows wiring.

5.5 Descaling the heating element

Scale deposits can affect heating capability and damage the element. Descale chemically or manually:

• Soak the element in white vinegar or another descaling solution.
• After descaling, rinse with fresh water and add baking soda.
• Alternatively, once dry, use a soft brush (non-metallic) to brush off mineral deposits.
• Reinstall the element with the gasket and make wire connections.

? NOTICE: Make sure the tank has been refilled with water before restoring power.

6 Replacement of parts

6.1 Changing the anode rod

• Turn off power and drain the heater (Section 5.2).
• Remove the heating element (previous section).
• Unscrew the anode rod from its threaded connection.
• Remove and replace the anode rod (Fig. 8 [N]).
• Reinstall the heating element.
• Refill the tank with water before restoring power.

6.2 Changing the heating element

• Turn off power and drain the heater (Section 5.2).
• Remove the heating element (Section 5.4).
• Install the new element with gasket, ensuring correct positioning. Tighten retaining nuts and make wire connections.
• Ensure the thermostat temperature sensor is inserted into the well on the element assembly and secured with the black rubber grommet.
• Refill the tank with water before restoring power.

6.3 Changing the thermostat

• Turn off power supply.
• Disconnect the two wire connectors from the thermostat.
• Loosen the two brass screws on the right side of the thermostat and pull wires out.
• Remove the thermostat temperature sensor from the well in the element assembly.
• Unscrew and remove the two Phillips screws holding the thermostat to the tank.
• Install the new thermostat and re-attach wiring and screws.
• Ensure the thermostat temperature sensor is inserted into the well on the element assembly and secured with the black rubber grommet.

7 Troubleshooting

7.1 Fault Assessment and Troubleshooting

7.2 Resetting High Limit Switch

The high temperature limit shut-off device may trip, usually when water temperature exceeds 190°F, or due to power outages or storms.

To reach the thermostat:

• Disconnect the power cord and remove the installation cover.
• Firmly press the reset button (Fig. 9 [B]) with a pen tip or similar object. A click indicates reset.
• Reconnect power.

IMPORTANT:

• Check thermostat operation: Turn temperature dial from high to low.
• If the red light does not turn off on low setting: Turn off power and call a technician to replace the thermostat.
• If the red light turns off, the thermostat is working. Set to desired temperature.

? NOTICE: A lower setting is more economical and reduces the risk of scalding.

Replace the cover plate.

CAUTION: Call a technician if the high limit needs to be reset frequently.

8 Interior components diagram

Diagram (Fig. 10) illustrates the interior components: