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Tankless Water Heater Troubleshooting

Is dirty water coming from the tankless water heater? Do you need to figure out how to shut off a constantly running water heater? Tankless water heaters provide hot water only when needed which is why they are often called ‘instantaneous’ or ‘on-demand’ water heaters. While these do away with the need for a storage tank, they do carry some disadvantages. Always consider the pros and cons when deciding between a tankless and storage water heating system. Ask an Expert for more information about them, their common problems and how to overcome them. Read below where verified Experts have answered questions for users. 

Why is the hot water from a tankless water heater dirty, and what can be done about it?

Sediment or scale has probably built up in the heater which needs to be flushed out. Connect a garden hose to the hose hookup near the bottom. Turn off the gas or power to the heater and shut off the inlet valve. Open the outlet valve and allow the heater to drain out fully. When the heater empties itself let some more water in by opening the inlet valve and repeat the process till only clear water flows through. If the water is still dirty the inlet piping may have corroded if it is galvanized.

How to repair a tankless water heater where the delivery is inconsistent?

Case details: The filter was recently cleaned. The heater works well initially, but after a while shuts itself off and makes a lot of noise. No error code is displayed.

There are two likely situations:

  • If shut off is affected through a gate valve the stem could have broken inside causing a blockage. The solution is to replace the gate valve.
  • The heat exchanger itself might be blocked, particularly if it has never ever been flushed or not flushed for a while. In normal maintenance, a tankless water heater heat exchanger should be flushed once a year at least to prevent scaling especially if the water is hard and high in mineral deposits. If there is a sediment build up the heat exchanger might need to be descaled or replaced. Flushing it with a pressure hose should be avoided as it could damage the inside of the exchanger.

Why does a tankless water heater sound like a jack hammer whenever water is not flowing through it?

From the description the problem does not appear to be the heater but more likely to be a bad well tank which is causing the pump to pulsate. This could be the case if the well tank bladder ruptures in which case no back pressure can be created. In the absence of pressure the pump will seek to maintain the set pressure causing the pump switch and pump to open and close frequently. An action like this imposes undue strain on the plumbing system. To test for it, depress the Schrader valve used for filling the tank and check the wall tank air pressure.

How to set the temperature beyond 120⁰ F on a brand new Rheem tankless water heater?

With the newer models a temperature reset should be possible using the remote and following these steps:

  • Turn on the remote.
  • Shut off the water and gas supply below the tankless heater.
  • When 120 degrees is reached press and hold the up arrow till the number flashes.
  • Press both up and down arrows together till the number stops flashing.
  • Turn on both water and gas supply to the unit.

Why is a 12-year old tankless water heater able to heat water but not able to deliver it to the outlet points?

Here are some possible reasons why this is happening:

  • The shut off valve could be broken in the closed position.
  • The tank might be filled with sediment which is clogging the heater.
  • The heat traps on top of the tank are fouled resulting in blocked tank nipples which prevent free flow of water.

A problem with a tankless water heater could be very frustrating especially if no solution is readily available. Here is where it helps to ask verified Experts who are always available to answer questions on any tankless water heater problems and help with repairs. If you need a solution to a tankless water heater problem, ask an Expert on JustAnswer today.

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