I installed a tankless heater and have temp changes. The book says I might have a "crossover issue". How do I know for sure? If this is so, How do I correct it? I have many single valve fixtures in the house. The heater book says "the heater will not run with too much backpressure".

Which brand did you buy, what is your fuel source and have you tried the customer support line for that manufacturer? Could you also give more detail to what you mean by temp changes. What did the manual refer to with cross over, I have know clue and I do this stuff.

What brand of tankless water heater do you have ?

Bosch Natural gas. I've heard that Bosch will not help but this is a common problem with tankless heaters

The hot water gets too hot in the kitchen sink, when you try & cool it off, it goes cold. You can't make warm water. It sounds like the backpressure from the cold side puts too much backflow on the hot side causing reverse flow. The book says this will shut the heater down.

Ghenle...

Most of the Bosch models have two knobs to adjust temperature. The temperature adjustment knob and the power adjustment knob... both located at bottom front.

It is usually a balance between the two knobs that allow this system to work properly.

Let us know the model number and we can see exactly which unit you have and can then advise best! Also wondering if you have a candy thermometer so you can take a temperature reading at all faucets... full hot? Let us know temps if you can (hi-temp. thermometer also sold at home depot or lowes).

MARK

PS.. I won't be on again until late tonight.

Hot water temp is 114degF @ Kitchen sink (closest to heater). 128 degF in upstairs Master bath sink (furthest from heater).Model is Bosch Aquastar 2400E NG. The thermostat is set @ 102degf right now.