New shower fixture is only allowing either hot or cold water and not a blend of both

the_new_guy

I recently installed a new shower fixture and for some reason, the thermo valve is only letting Cold, or Hot water and not a blend of both of them. As I turn the thermo valve I can feel a sudden change of pressure from Cold to Hot, or Hot to Cold when turned the other way.

I've tried replacing the cartridge twice, as this type of issue is usually because of a defective cartridge. However, that did not help at all.

I only have this issue with the new shower fixture and not with other showers in the house, or even the previous shower fixture that was replaced.

Because the thermo valve is only letting Hot water in, the water gets too hot; and when thermo valve lets cold water out, it eventually gets too cold to tolerate.

I purchased the shower fixture from Bath Depot. The model is KEBO S8T-3883CH.

link: https://www.bathdepot.ca/en/chrome-square-thermostatic-shower-faucet-with-rain-showerhead-s8t-3883ch.html

Any help or suggestion is much appreciated!

Ryan

Intplm.

Hello Ryan
@the_new_guy
You are correct when saying this is a defective cartridge. Replacing it should have corrected the problem. I often call this a ghosting or hunting problem when the thermostatic cartridge is defective and tries to, but cannot find a steady temperature but hunts for a temp.
The hard part about this is that there might be a washer or gasket doubled up from the factory and or from your repairs that you are not aware of.

hot_rod

is the pressure the same  on hot and cold? A wide pressure difference can cause thermostatic valves to hunt

Temperature on the hot needs to be about 20 degrees hotter than mix for stable operation on thermostatic valves

Usually they fail to cold however, under those conditions 

Intplm.

@the_new_guy .

@hot_rod makes a very good point here. These cartridges are commonly described as pressure-balanced.
They are designed to stop the old joke of flushing the toilet while someone is taking a shower and having the water suddenly go cold, or was it hot? Remember that old prank?

It is a safety precaution

So the pressure needs to be in line with the specs of the valve.
Look into the above thoughts. Hopefully, you can find a solution.

dwhipps

I have this exact same problem, with the exact same model. I replaced all three cartriges and the problem got worse! The water shuts off completely when turning from cold to warm/hot. What's the resolution here?

JUGHNE

Just a long shot…….could the H&C supplies be reversed in the wall.

hot_rod

shower valves can be pressure balance or a combination of pressure and temperature

The valve spec sheet will tell you the required conditions.

I know some mixing valves struggle with tankless coil dhw as they can have a lot of pressure drop as they lime up. I suspect tankless water heaters could also cause too much pressure drop on one side of the valves.

60 psi on the cold, hot drops to maybe 40 due to restricted coil

This is the first question tech support will, or should, ask, what is supplying the hot water?

Valve seeing imbalance of pressure or temperature will typically fail to cold

So…you would need to measure pressure at hot and cold while it is flowing, dynamic pressure, and confirm the hot is above the valves requirement

Plugged strainers can cause big pressure drops also At one of a mix valves ports

its hard to believe 3 cartridges are defective? I think it is application related