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Posted by HeatPro on July 16, 2009 at 10:09:16:
In Reply to: Tankless Hot Water Heater Problem posted by Jam on July 16, 2009 at 08:01:47:
: I recently purchased a Bosch Tankless Pro for my home. We really enjoy it, especially with 4 of us in the house!
You'll notice, as everyone else does, that you didn't tell the model, so the flow rate and instructions for them can't be found to give an answer.
Try to find the Installation and Operation instructions that came in the box to see if you can lower the water temperature control. Aside from that, the larger the burtner input, the more the minimum flow rate required to fire the boiler; thus you get the on-off operation you describe.
The smallest one, the 260 PN, requires a flow just a little larger than the 2-1/4 gpm flow rate of a shower head; larger units require even more.
Essentially, if you have the 425 units, you fire off enough gas to heat a 4000 sq ft house each time you turn on a water tap; that is one of the downsides of such big burners for hot water, and one reason why people install 40 gallon tank-type water heaters with a 40,000 btu burner instead of a 125,000 btuh tankless.
http://www.plumbingsupply.com/protanklesswaterheaters.html