How to a Replace Hydro Generator on Bosch 520

Learn how to replace a Hydro Generator on Bosch water heaters from 520 series?

The hydro generator, which is found on Bosch tankless water heater from the 520 series, works like a small turbine that creates a spark to ignite the gas when there is a call for water heating.

What is needed to run this turbine is the water flow and pressure, but not the electricity.

This is what makes Bosch 520 models great, especially for vacation homes, cottages, and homes in general affected by frequent power outages. As long as you have an unobstructed supply of gas and water, you will enjoy a decent shower.

But if you have a problem with the Hydro Generator, this is what is needed to replace it.

Required tools

  • Phillips-type screwdriver
  • Flat-head screwdriver
  • Multi-meter
  • Bucket
  • Cloth


NoteProfessional installation and repair are recommended. Find local plumbers and get FREE Quotes!

  • Turn off the main gas shut-off valve that supplies the water heater.
  • Turn off the main water shut-off valve that supplies the unit. It is usually located close to the water heater.
  • Open the hot water tap (the lowest located) to relieve the pressure from the unit and drain the tank.
  • Locate the water valve, put the bucket under, remove the retaining clip and the bushing.
  • Once the bushing has been removed, there will be some water coming out from the heater and the water lines.
  • Locate the Hydro Generator and disconnect the wire connector.
  • At this point, you can measure the voltage at the hydro-generator to see if it is getting enough voltage. The wires can be blue and brown, and the voltage should be at least 2.8 VAC, or if the wires are black and red, the voltage should be at least 1.3 VDC. Any other measurement (value) means the problem.
  • Remove both clips from the Hydro Generator, disconnect and separate the water pipes.
  • The Hydro Generator is now removed, and the new one should be put back in reverse order.
  • Make sure that the piping, clips, and inlet filter are correctly installed.
  • Open the main water shut off valve to check for possible leaks.
  • If there are no leaks, open the gas supply and resume the water heating operation by turning the unit ON.

Check out a detailed guide here.

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