Electric Water Heaters Troubleshooting

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the T3 sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to T3 and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the T4 sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to T4 and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the TP sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to TP and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the display board are tight.
• If no - Go to Step 2.

Step 2. Check incoming power and breaker size.

• Test for VAC across L1 and L2.
• Check what the breaker size is.

Results:

• If on site with tools, contact the Bosch technical support specialists

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• • If yes – Could be connection issue. Confirm the wire connections for the fan are tight.
  • If no – Could be open sensor or connection issue. Go to Step 2.

Step 2. Is the fan running?

• YES/NO Go to step 3.

Step 3. Checking wiring connections

• Check all low voltage wiring for proper connection and contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections to the heating elements are tight.
• If no - Go to Step 2.

Step 2. Check OHMS on each element

Shut power off to the unit and confirm no power at the L1/L2 of the terminal block.

• Set their digital multi-meter to ohms.
• Place a probe on each of the ends of the top element.
• Record the ohm reading.
• Place a probe on each of the ends of the bottom element.
• Record the ohm reading.

Results:

• If reading 12.8 OHMS (+/- 10%) go to step 3.
• If reading open or outside of 12.8 ohms (+/- 10%), replace that element. Confirm part number.

Step 3. Checking wire connections to the elements.

Confirm that the wire connections to the elements are tight and that the wires are not damaged.

Results:

• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the TH sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to TH and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the T5L sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to T5L and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the T5U sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to T5U and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle?

• YES – Could be connection issue. Ensure all wire connections are tight.
• NO – Go to step 2.

Step 2. If on site with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle?

• YES – Could be connection issue. Ensure all wire connections are tight.
• NO – Go to step 2.

Step 2. Check if auto shut-off valve is installed. The auto shut-off valve is an accessory and not required.

• YES – Check for tight wire connection to auto shut-off valve.
  • If they were loose, the error should go away.
  • If they were tight, go to step 3.
• NO – Go to step 3.

Step 3. Check auto shut-off valve setting.

• Go into advanced settings on the control by holding the settings button for 3 seconds.
• Use the Up/Down arrows to scroll down to F38.
• Use the "Check" button in the bottom row on the right.
• Change the setting to "0".
• Hit the "Back" button to the left of the "Check" button to save this change.
• If on site with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the TP sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to TP and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections for the T5U sensor are tight.
• If no – Go to Step 2.

Step 2. Check the sensor through the display to see the reading

• To check the reading, press the settings button on the control panel.
• Using the Up and Down arrows, scroll down to T5U and record the numbers in the center of the display.
• Contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – Find breaker size and if onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be power supply issue. Put the unit back in service and monitor it for further errors.
• If no – If onsite with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections are tight.
• If no – Could be open sensor or connection issue. Go to Step 2.

Step 2. Check ambient air temp

Is the air around the unit below 39°F? YES/NO

• YES – likely too cold for machine. Increase the temperature of the air around the unit.
• NO – If the caller is a technician on site with tools, contact the Bosch technical support specialists.

Digital Multi-meter

Step 1. Power Cycle

Does the unit reset after power cycle: YES/NO

Results:

• If yes – Could be connection issue. Confirm the wire connections are tight.
• If no – Could be open sensor or connection issue. Go to Step 2.

Step 2. Check the condensate drain

Is the condensate drain clean? YES/NO

• YES – Contact the Bosch technical support specialists.
• NO – need to clean drain

• FLOW RATE IS TOO LOW - Verify flow rate out of fixture is at or above the minimum .8GPM required for the unit to activate.
• THE WATER SUPPLY IS CONNECTED TO THE OUTLET OF THE UNIT - Verify plumbing connections are correct. See: TWH E2-01. Reconnect the water supply to the inlet of the unit (marked blue).
• ONE OR MORE OF THE HEATING MODULE THERMAL CUT-OUTS HAS TRIPPED - Turn off the power to the heater, remove the cover and locate thermal cutouts on the top of each heating module. Try resetting each cutout by pushing the red reset button located in the center of the cutout. Establish and fix the cause of the overheating. Obstructions in the water path can restrict the flow of water through the heater causing it to overheat. Verify the heater’s inlet filter screen and all outlets served by the heater are clear of debris. Ensure the heater is not being fed preheated water. This water heater is designed for a cold water feed only. If thermal cut outs keep tripping, check for continuity through the elements. See: TWH E2-02.
• PLUMBING CROSSOVER - To test for a plumbing crossover, turn off power supply to the heater. Close installer supplied cold water shut off valve (if none installed, install before proceeding). Open all hot water taps supplied by the heater. Wait 10 minutes and check all faucets. Any water running is a sign of a plumbing crossover. Consult a local plumber or service person for help in correcting a plumbing crossover. To return the heater to service, reinstall cover, open the inlet water supply to the heater and open all hot water taps. Let all taps run until there is no air coming out of the fixtures. Shut off all hot water taps. Turn power supply on to the heater. Return heater to service. (this procedure will prevent the heating elements from dry firing).
• THE FLOW TRANSDUCER IS NOT SPINNING - Turn off the power supply to the heater and remove the cover. Observe if the flow transducer "spins" when the water is turned on. Please note the flow transducer spins at a high speed and can appear to be stopped when actually spinning. It is recommended to observe the flow transducer without water flowing, then turn on a hot water tap while observing the flow transducer. If the flow transducer is not spinning remove, and flush flow transducer. See: TWH E2-21. Contact Technical Support if flushing does not work.
• NO ELECTRICITY AT THE HEATER OR ONE OF THE SUPPLIES HAS FAILED - Have a licensed electrician verify proper wiring and adequate voltage on the terminal block inside the water heater. See: TWH E2-01.

• THERE ARE RESTRICTIONS IN THE PLUMBING - Obstructions in the water path can restrict the flow of water through the heater. Verify the heater’s inlet filter screen, faucet aerators, showerheads and whole house filters are clear of debris. Verify proper flow on the outlet side of the heater with the hot water pipe disconnected. Maximum flow rates for each unit are as follows. RP17PT = 2.3gpm, RP27PT = 3.5gpm.
• WATER SUPPLY PRESSURE TOO LOW - Verify incoming water supply is at least 30psi. For people on well systems, the recommended pressure range is 30-50psi.
• OUTLET SHUT-OFF VALVES ARE SET TOO LOW - Adjust installer supplied outlet valve as described here: a) Completely open both installer supplied inlet and outlet shut-off valves at the heater. (if none installed, install before proceeding; b) Completely open hot water on the highest flowing hot water fixture served by the heater (i.e. bathtub); c) Slowly close the outlet shut-off valve, slowing the water flow rate until the temperature at the hot water faucet corresponds to the values given on Graph 1 on Page 8 of the manual, or desired water temperature is reached.

• TEMPERATURE DIAL IS TURNED TOO LOW - Turn the temperature dial located on the bottom of the water heater clockwise for hotter temperatures.
• WATER FLOW TOO HIGH - Adjust water flow to stay within the water heater’s specifications. See: TWH E2-03. Refer to Graph 1 on Page 8 of the manual.
• ONE OR MORE OF THE HEATING MODULE THERMAL CUT-OUTS HAS TRIPPED - Shut off the power to the unit, remove the cover and locate thermal cutouts on the top of each heating module. Try resetting each cutout by pushing the red reset button located in the center of the cutout. Establish and fix the cause of the overheating. Obstructions in the water path can restrict the flow of water through the heater causing it to overheat. Verify the heater’s inlet filter screen and all outlets served by the heater are clear of debris. Ensure the heater is not being fed preheated water. This water heater is designed for a cold water feed only.
• THE POWER SUPPLY VOLTAGE HAS DROPPED - This is likely an issue with the incoming power supply. Measure voltage on the water heater’s terminal block while operating at maximum flow and maximum temperature setting. The RP27PT and RP17PT models are rated for 240V and will also operate at 220V or 208V with reduced output. The output will vary in accordance with the following ratios: volts 208 output ratio 75%, volts 220 output ratio 84% and volts 240 output ratio 100%.
• THE INLET WATER TEMPERATURE IS TOO COLD - Verify the heater is sized appropriately for it’s geographic location. Turn temperature knob located on the bottom of the water all the way clockwise for maximum temperature setting. Ensure flow rates are within the heater’s specifications. Refer to Graph 1 on Page 8 of the manual. Use of an isolation valve on the hot water outlet to control flow rate is recommended.
• ONE OF THE POWER SUPPLIES IS NOT ON - Have a licensed electrician verify adequate voltage on the terminal block inside the water heater, Verify circuit breakers serving the heater are not tripped. Check the supply voltages. PREMATURE ELEMENT FAILURE - Shut off power to the unit and remove cover. Use an ohm meter to verify correct resistance on each element. See: TWH E2-02. If readings are different than listed specifications, contact Technical Support for further instruction.

• COLD MIX, HEATER DEACTIVATES - If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04.
• FLUCTUATING WATER PRESSURE - If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
• CHANGING FLOW RATE - Major changes in low rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater’s specifications. See: TWH E2-03.

• Be certain power and breaker at panel box are on.
• Water supply to unit must be connected to proper fitting.
• The high temperature thermal cut-out has been triggered. Turn off power to unit , remove front cover and reset thermal cut-out. Locate of thermal cut-out. Thermal cut-out button should push in and click, if it does not but rather feels stiff and wobbly then it is not the problem.
• If the power and reset are all right then the flow switch in the heater needs to be inspected. See parts diagram. The unit may be mounted on wall in a different orientation then this diagram but in this diagram the plastic (white or black) plunger with screw on the stem needs to move laterally to the left with sufficient water flow. Best to test by leaving faucet open and controlling water flow to heater with an inlet or outlet service valve directly before or after the heater, this way the flow switch can be observed. If water continues to flow at sink while service valve is turned off then this plumbing error will prevent the flow switch from pressurizing and needs to be corrected. If plumbing is all right but the flow switch doesn't move then either the flow is insufficient or the flow switch is stuck from use or water quality. Improve flow rate by cleaning filter screen and aerator screen at sink, also remove aerator screen/restrictor at sink to improve flow as a test.

• Inlet water is preheated. This unit does not recognize preheated water and is designed to be plumbed with cold water.
• The heater will boost inlet water temperature as water flows through it. To lower outlet temperature first position the selector screw to the LO setting. See diagram with LO and HI markings. Turn off power, remove front cover, loosen selector screw and then slide all the way to LO setting and retighten. Selector screw has to be positioned to either end of slot, do not position it midway. If temperatures are now too cool then it is best to put screw back to HI setting and follow step 3.
• The rate of water flow will effect the outlet temperature, the greater it is the less time the heater is capable of heating as it passes through it. Increase flow rate by cleaning filter screen, aerator screen at sink and check to be sure inlet and outlet service valves are fully open. Removing restrictors at faucet will also increase flow rate. Location of filter screen, marked filter plug.

• Inlet water is preheated. This unit does not recognize preheated water and is designed to be plumbed with cold water.
• The heater will boost inlet water temperature as water flows through it. To lower outlet temperature first position the selector screw to the LO setting. See diagram with LO and HI markings. Turn off power, remove front cover, loosen selector screw and then slide all the way to LO setting and retighten. Selector screw has to be positioned to either end of slot, do not position it midway. If temperatures are now too cool then it is best to put screw back to HI setting and follow step 3.
• The outlet temperature is determined by the inlet water temperature and flow rate. The higher the flow rate, the lower the outlet temperature; the lower the flow rate, the higher the outlet temperature. Increase flow rate by cleaning filter screen, aerator screen at sink and check to be sure inlet and outlet service valves are fully open. Removing restrictors at faucet will also increase flow rate. Location of filter screen, marked filter plug.

• While running hot water observe the neon light on the front of unit. The light should remain on during hot water use, if it goes out then likely the water pressure is fluctuating, flow rate is barely sufficient and causing the flow switch to cycle on and off. To improve flow rate, check to be sure inlet and outlet service valves are not tightened too much, clean inlet fitler screen and faucet aerator screen. Removing restrictors at faucet will also increase flow rate. Location of filter screen, marked filter plug. If inlet water is warm because of climate or season then it is recommended that the selector screw in heater be positioned to the LO setting. Turn off power, remove front cover and loosen selector screw. Then slide screw to LO setting all the way and retighten. NOTE: this heater is designed to be plumbed with cold water and is not designed to be used as a booster, do not plumb unit with preheated water.

• It is important that the plumbing not have any check valves or back flow prevention devices before the heater. These devices can prevent thermal expansion and cause pressures to exceed 150 psi. The excess pressure may cause the pressure/temperature relief valve to discharge, and may cause premature failure of the element gasket.
• Use the supplied pressure/temperature relief valve for the heater. If an alternate is used, ensure the valve is rated for a maximum pressure of 150 psi and a max water temperature of 210F. The temperature probe should not extend beyond 4 inches in order to maintain adequate distance from the heating element.
• When filling tank, leave hot outlet tap at sink open while filling to displace all air in tank. Do not energize heater until all air is out of tank. Energizing the heater dry will cause element failure.

• If the water temperature is too hot, adjusting the thermostat counter clockwise will lower the temperature. See: Setting thermostat.
• If the water temperature is too cold, adjusting the thermostat clockwise will lower the temperature. See: Setting thermostat.
• When the heater has reached the temperature set by the thermostat, the indicator light will go off. If the temperature is not at the desired set point, adjust as outlined in either step 1 or 2.

• If the indicator light does not illuminate when adjusting thermostat clockwise: a) Check that the switch is in the ON (I) position; b) Verify the outlet is energized by plugging in a known good appliance such as a lamp. For the GL8 ProTi model, check voltage with a voltmeter to be 110VAC; c) If outlet is good, unplug the heater and remove the front cover. In the middle of the thermostat, there is a small square opening housing the reset button. Attempt to reset by pushing in with a pen point or small screwdriver. If a thermostat requires frequent resetting or cannot be reset, the thermostat may be defective and need replacing; d) If the indicator light still does not come on, the thermostat is defective and needs replacing. Check thermostat; e) If the indicator light works, without any temperature change after 30 minutes, the element should be replaced.

• Water leaking from either water fitting connection: a) Inspect the fittings; b) If they are corroded, replace the fittings. The openings are part of the inner tank and cannot be repaired. The tank should be replaced. Read warranty statement.
• Water relieving from the pressure/temperature relief valve: a) Verify the relief valve rated for a maximum pressure of 150 psi and a max water temperature of 210F. The temperature probe should not extend beyond 4 inches in order to maintain adequate distance from the heating element; b) If any plumbing work has been done recently, verify there are no backflow prevention devices installed on the cold side of the tank. Backflow prevention devices can prevent thermal expansion and cause pressures to exceed 150 psi. Check the building inlet water pressure. A faulty water pressure regulator can cause pressures to exceed the 150 psi; c) Observe the thermostat indicator light while heating. When the heater has reached the temperature set point, the indicator light should go out to prevent overheating. If the water being discharged is steaming and the indicator light is still on while discharging the thermostat is defective and should be replaced.
• Water leaking from behind the front cover: a) Disconnect the plug from the outlet; b) Remove front cover and inspect the gasket around the element. If leaking from the gasket, replace gasket.
• A water leak from any other location on the tank cannot be repaired and the tank should be replaced. Read warranty statement.

• There is a magnesium anode rod in the heater that will slowly deteriorate during use. It is designed to absorb minerals in the water in order to protect the element. The rate of deterioration depends on water quality. When the anode rod is spent, water may become discolored or smelly. It is important to inspect and replace the anode when it is spent to prevent damage to the tank or the element.
• It is recommended that you inspect the anode rod annually.