How is this Symmons shower faucet SUPPOSED to work ('cuz it doesn't work that way)

How is this Symmons shower faucet SUPPOSED to work? ('cuz it doesn't work the way I think it should)
https://c2.staticflickr.com/6/5601/15092308233_6552db0147_b.jpg
What happens, no matter where I put the volume control knob or the temperature control lever, is that the water comes out blazing hot.
I can't lower the temperature any further on the hotwater heater itself, because the rest of the house has similar set-and-forget shower faucets, which, the family tells me, is just right.
Isn't the lever, which goes from the 9 o'clock to 6 o'clock position, *supposed* to regulate the temperature?
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Danny,
Plumbing manufacturers usually have great customer service. http://www.symmons.com/Customer-Service.aspx
Dave M.
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