Effects of sediment and different water sources.

Sediment is small particles and debris in the water, it may be tiny rocks, clay, pieces of wood and other organic material carried in and by the water.

Sediment makes its way into water lines and into the tankless water heaters.

Today, most tankless units, gas and electric, are flow activated. This means that the way the units start is by flow of water running through them. You open the water faucet, water will run into the inlet of the water heater and make the impeller spin. The impeller is just like a propeller inside the inlet fitting. The spinning of the impeller sends a signal for the unit telling there is water running and that it should come on and heat the water.

The problem is that sediment may be small enough to get through the inlet fitting screen and clog the impeller. If the impeller does not spin it won’t signal the water flow to the unit and it will not start and heat the water.

The unit will be like a sitting duck. Water will be running, there will be power available, it won’t show any errors but it will just sit there and not heat the water.

In the picture below you can see the small particles of sediment that clogged a gas power unit:

In the following video, you may watch how to clean the impeller and inlet fitting screen on Marey’s Eco electric line: ECO110, ECO150, ECO180, ECO240 and ECO270.


Unfortunately, we cannot disassemble all inlet fittings and impeller of all models.

For the gas units of these lines: GA 5 and 10 FLOW, GA 24CSA and 14CSA, if the unit shows signs of a clogged impeller, you may try blowing compressed air into the inlet fitting in an attempt to free the impeller from the sediment. If this procedure does not work, the water flow sensor or water flow sensor valve must be replaced.

Below you may see the water flow sensor valve of a gas flow unit:

The impeller for the 24CSA line is in the water proportional valve, which can be seen on the manual, on page 46, number 7 on the diagram:

Gas Unit 4


  • Usually, there is less sediment in city water.
  • Well water and off-grid water sources usually carry a lot of sediment.
  • An easy way to prevent sediment and debris in the water is to install a sediment filter.
  • When and if you install a sediment filter, be careful not to decrease too much the water pressure and flow on the system. With low water pressure and flow the water heater may not start or may overheat.
  • It is very common to have clogs right after installations. So, purge the water line well before connecting it to the unit.
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