Whistling Shower, pressure issue?

[helpfuljoe]

We had a new shower installed a few months ago, and consistently get a loud whistling sound when we turn the shower temp hotter. The contractor and his plumber have been back twice, (1) flushed out the shower head, and (2) the 2nd time flushed out the hot/cold value. Both times did not fix the whistling. When I inspected the supply lines for the hot and cold to the shower, I found the cold water supply line for the shower comes from the water main before the pressure reducing valve, while the hot water goes through the reducer value and the hot water tank. Therefore, my theory is the cold is coming through at a higher pressure and causing the whistling when we turn the shower temp hotter (since the opening for cold gets smaller). Is this a sound theory? Thank you for the help!

Pic attached.

 

[Geofd]

Is the other tee before the prv a bypass or another line
Is it possible for you to valve off the hot?????
If so you could remove the shower head thread a pressure gauge on
And one at a time turn on the hot
The after turning off the hot
Turn the cold on
Then you would know the pressure differences
Maybe send the plumber pics if there is a big difference
Then he would have to move the tie in spot

 

[helpfuljoe]

Thank you @Geofd for the reply!

The other tee before the PRV is actually the outside sprinklers (not sure why those are coming out before the prv).
Yes I can turn off the hot supply to the shower a shutoff.. great idea on measuring the pressure differences I will do that!

Thank you!

 

[Geofd]

Thank you @Geofd for the reply!

The other tee before the PRV is actually the outside sprinklers (not sure why those are coming out before the prv).
Yes I can turn off the hot supply to the shower a shutoff.. great idea on measuring the pressure differences I will do that!

Thank you!

You could also put a gauge on that line......maybe over kill,

 

[helpfuljoe]

Update for anyone interested and @Geofd...

Even without the pressure gauge it was easy to see when the hot was off and the cold all the way on, the pressure was much higher with just cold.

Fix: Plumber today added a 2nd PRV on the shower cold supply and set both PRVs to the same pressure (75). So far, no whistling! Keeping an eye on it.

 

[Geofd]

Update for anyone interested and @Geofd...

Even without the pressure gauge it was easy to see when the hot was off and the cold all the way on, the pressure was much higher with just cold.

Fix: Plumber today added a 2nd PRV on the shower cold supply and set both PRVs to the same pressure (75). So far, no whistling! Keeping an eye on it.

Glad it worked out