My house uses well water, and the water from my tankless heater often runs cold. What's going on?

Asked by Ronald Symecko, Sugar Land, TX

I recently bought a six-year-old house with an electric tankless water heater. The house uses very hard water from a well. My hot water alternates from hot to very cold with only one water source running. Could scale and hard water deposits affect the ability of the heater to keep the hot water running?


Kevin Burrell

Answered by Kevin Burrell

Sausalito, CA

Kiwi Plumbing

April 19, 2007

I have a house that had the same problem with a gas on-demand water heater, so I think I know what is causing the trouble.

With a well and pump system, the water flow may not be strong enough to turn the flow switch on at the tankless water heater. The flow switch requires 13 gallons per minute running through it to operate. With some well systems, the pump will cycle on and off and drop the flow down to next to nothing and then back up again. This will cause the on-demand water heater to cycle on and off.

To fix this problem you'll need to replace the pressure-compensating tank at the pump. I estimate this would cost about $500.

Tagged In: green plumbing, tankless

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