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Remodeled our master bath. Bought a delta shower system. Double lever valve. One lever controls on/off the other lever in front controls hot and cold water. You would think putting the lever in the middle upright position would give warm water, it does not. I can only get burning hot. Or ice cold. First try we had not cold water or warm water, only hot. Changed the cold cartridge and now only hot or ice cold.

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    Check if the cartridge is correctly installed. Also check for pipe obstructions, and try without a water-saver shower head, to see if it's restricting flow too much. Aug 15 at 5:35
  • Is it safe to assume that this is a brand new install? Are the cartridges installed correctly? It's possible, though not likely, that they were bad from the factory.
    – FreeMan
    Sep 15 at 14:31
  • My bath mixer (and handspray shower) is a bit like this - more than a tiny bit of cold turned on, and you get cold water. The usable range is both narrow and right nest to fully hot. If you start fully hot, then nudge in small increments towards cold, are you sure it suddenly flips without passing through a tiny region of variability? This region could be expanded by a pressure reducing valve in the cold.
    – Chris H
    Sep 15 at 15:54
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Maybe a back flow preventer is missing or defect. Normally, the cold water has higher (dynamic) pressure, since the hot water must flow through a heat exchanger somewhere near the heating system. And hot water tubes tend to have more residuals like lime stone coatings which decrease the throughput even more.

So as long as the cold water is flowing at the shower, it would press back any hot water. Result is cold water at the shower head. Only if the cold water is shut off, the hot water can reach to the shower head.

Many shower mixers have 2 BFP. And those BFP are prone to fail, they must be replaced after some years.

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  • This is reasonable, however the implication I'm reading is that the OP has just recently remodeled the bathroom and the only hot/only cold water state is the only one she's experienced. This doesn't appear to be a 20-y-o faucet that's failing, it's a brand new one.
    – FreeMan
    Sep 15 at 14:31

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