Please help me diagnose this plumbing problem

February 23, 2019 8:45 AM

We have this thermostatic shower fixture. The cold water does not flow --- we turn the lower knob to start the water, but only hot water comes out. The shower is at full pressure when the thermostat is all the way to hot, and as we turn the upper knob down in temperature the pressure gets lower and lower, until the temperature is all the way to cold and no water is flowing even though the on/off knob is still all the way "on."

The plumber has already visited and replaced the thermostatic cartridge (#3 in the diagram), with no change in the behavior. What else could be the problem and how can we diagnose it?

posted by slenderloris to Home & Garden (5 answers total)

This makes me think that the shower fixture itself is actually working properly - after all, the hot water is acting exactly as it should - but something is wrong with your cold water connection in or before your shower head itself so that it's not actually producing any water.
posted by brainmouse at 9:07 AM on February 23, 2019 [2 favorites]

Was it ever working correctly? When mine was installed, this behaviour was due to cold and hot water being swapped around.
posted by I claim sanctuary at 2:23 PM on February 23, 2019

The swapped lines makes sense. It also makes sense that the cold line might be plugged prior to the mixing valve. Did it work at one time? If so, that suggests the cold line has an obstruction.
posted by Gilgamesh's Chauffeur at 8:56 PM on February 23, 2019

Response by poster: We took off more and more pieces and eventually discovered gears like these controlling the valves, one of which (the cold one, obviously) did not appear to be operating properly. Replacement gears and valves have been ordered and we'll see how it goes.
posted by slenderloris at 11:13 AM on February 25, 2019

Response by poster: Not that anyone cares, but we did eventually fix this basically ourselves (a while back; we have not been going without showers for 6 months, haha).

The existing inoperable gear had to be pried off the nut with a fair amount of force due to calcification, but once that was done it was pretty easy to replace the gearsets and get it back together.

Relevant search terms are Dornbracht Tara Concealed Thermostatic Mixer and Trevi Shower Gear Box Assembly for the bots' indexing pleasure. Feel free to contact me via MeFi Mail!
posted by slenderloris at 3:44 PM on August 20, 2019