Hot tap goes cold when closing the cold tap

[danmessem]

Spent the last hour looking for an answer online - now you are my only hope to stop the dark side from taking over and freeing my hot water

I have a shower on the 1st floor - I 1st time I tried to use the shower, the shower ran luke warm and then cold as I turned the lever to warm.

To assist in troubleshooting, I have removed the shower and installed temporary taps to on the hot and cold outlets on the wall.

When I open both taps, the hot tap runs hot, and the cold tap runs cold.
When I then close the cold tap, the hot tap runs cold.
I am stumped - what could the issue be?

 

[Caduceus]

When you close the hot only, does the cold stay cold?
Also, some background helps. Did the fixture ever work okay before this problem? Is this a new home or just new to you (just purchased)? Have there been any changes to the plumbing recently or remodeling work or contractors in the home?
Are the other fixtures working properly in the home?
It seems like you are describing a crossover between the hot and cold somewhere in the house.

 

[danmessem]

Turns out that whoever installed the shower decided that it would be a good idea to connect the hot and cold pipes together with another pipe

 

[danmessem]

the guys who installed the shower told me they could "plumbing good"

so my fault I guess

 

[Caduceus]

So is this considered problem discovered and solved?lol.

 

[Matt30]

Make shift mixing valve I guess!

 

[danmessem]

So is this considered problem discovered and solved?lol.

Not until I get my hands on whoever installed the shower!