I had a Bosch Aqua star GWH 2400es-ng tankless water heater installed last May 2010 by an general contractor. I have already noticed a few issues. First off while in the shower the water will cycle between hot and cold, even when no other water source is used. It irritates me to have to fine tune this throughout my shower.

Secondly, when drawing water from the bath faucet it never gets as hot as the shower head. How can I correct this? I called Bosch tech support and was asked how high I had my heater set at (126 deg) and was told it was too high and they suggested setting to 118 deg, as bath water is normally 105 deg range. They explained that my system has been cycling because of this, as it's trying to reach that desired temp. I am not certain how it would cause it to cycle, but I did lower it to 118 deg. I have not seen any changes since turning it down. And while in the shower my water turned completely cold because the sink faucet was being used! Since my tankless water heater should support two major appliances I was very upset about this. I was told that this is d/t low water pressure, and that it needed to be 2 1/2 ppm.

How do I check my water pressure?

Also, while investigating this I performed another test to see if I had a plumbing crossover... and I do :( I have single faucet handles on both my downstairs sink & stand up shower and single faucet handles in my kitchen and upstairs bath. The only double faucet handle I have is the upstairs bath vanity. Would this be part of the issue?

Is fixing a plumbing crossover difficult? Expensive?

Please help!