I recently replace my water heater with a tankless water heater. I purchase the Aquastar 250SX gas unit. The unit works great if I'm running hot water only. It will continuously give me hot water as long as I want it. However, when I want to reduce the tempurature by turning on the cold water, the water goes cold in 10 min. I turn off the cold water and wait for the water to heat up again in. At first, I thought is was a cross-over issue. But what I turn off the hot water line, the water stopped running from the hot faucet. I am now guessing that the pressure from the cold water line is reducing the flow rate from the hot water line and causing the tankless water heater to stop burning. Does anyone have a similar issue that I'm having? :confused:

It sounds exactly like the one problem I saw causing me to not buy a tankless heater. Check, there is a spec for the minimum flow rate. Turn the water down too far, and the heat goes off. You may be able to work around it by reducing the set temperature. That way you will use more, but lower temperature water.

If you do a search here, you can find where I question if tankless heaters are a good idea.

I would turn the temp up on the tankless heater so the mixing doesn't cool it down so quickly and drastically.

Handyman2007: You are responding to 5 year old post.

Maybe someone should get Ask to eliminate posts that are 6 months or older... hmmmmm