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Bosch Powerstream Pro RP27PT Electric Tankless Water Heater Troubleshooting Guide

Please note: If you are unable to perform the tasks listed below or need additional assistance, please contact your original installer/licensed gas technician. This model is for indoor installation only.

Cold Water Only - Neon Light Off?

1. FLOW RATE IS TOO LOW
   Verify flow rate out of fixture is at or above the minimum .8GPM required for the unit to activate.
2. THE WATER SUPPLY IS CONNECTED TO THE OUTLET OF THE UNIT
   Verify plumbing connections are correct. See: TWH E2-01 Light off, water not hot [PDF]. Reconnect the water supply to the inlet of the unit (marked blue).
3. 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 Light on, Water not hot [PDF].
4. 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 5 minutes and check all taps. 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).
5. 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 Replacing Transducer [PDF]. Contact Technical Support (866) 330-2729, if flushing does not work.
6. 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.

Water Too Cold - Neon Light On?

1. TEMPERATURE DIAL IS TURNED TOO LOW
   Turn the temperature dial located on the bottom of the water heater clockwise for hotter temperatures.
2. WATER FLOW TOO HIGH
   Adjust water flow to stay within the water heater’s specifications. See: TWH E2-03 Outlet Temperature vs. Flow Rate [PDF]. Refer to Graph 1 on Page 8 of the manual.
3. 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.
4. 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 AE-115/AE-125 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%
5. 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.
6. 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.
7. 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 Light on, Water not hot [PDF]. If readings are different than listed specifications, contact Technical Support (866) 330-2729 for further instruction.

Water Flow Too Low?

1. 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. AE-115 = 2.3gpm, AE-125 = 3.5gpm.
2. 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.
3. OUTLET SHUT-OFF VALVES ARE SET TOO LOW Adjust installer supplied outlet valve as described below:
   1. Completely open both installer supplied inlet and outlet shut-off valves at the heater. (if none installed, install before proceeding
   2. Completely open hot water on the highest flowing hot water fixture served by the heater (i.e. bathtub).
   3. 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.

Water Temperature Too Hot?

1. TEMPERATURE DIAL SET TOO HIGH
   Turn the temperature dial located on the bottom of the water heater counterclockwise for cooler temperatures.
2. THERE ARE RESTRICTIONS IN THE PLUMBING
   Obstructions in the water path can restrict the flow of water through the heater causing overheating. 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. AE115 - 2.3gpm, AE125 - 3.5gpm.
3. INLET WATER TEMPERATURE IS TOO WARM
   Verify the heater is being feed with cold water only. This water heater is not designed for preheated water or recirculation applications. Increase flow rate where ever possible. Replacing low flow showerheads and aerators with higher flowing (GPM) ones may be necessary. .

Water Temperature Fluctuates?

1. 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 Overcoming fluctuating temperatures [PDF].
2. 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.
3. CHANGING FLOW RATE
   Major changes in flow 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.

Information Source: Bosch Water Heating