On Tuesday, May 23, 2017 at 8:40:15 PM UTC-4, Thomas wrote:
On Tuesday, May 23, 2017 at 2:14:08 PM UTC-4, trader_4 wrote:
Here's a baffling problem. Over maybe the last year or so, the water
flow in the shower has decreased. It's happened slowly, so not sure
when it really started, but lately it's become a problem. It's not
the shower head, I removed it and the flow right out of the 1/2"
pipe from both the hot and cold are way below what they should be.
But here's the bizarre part. If I open just the cold all the way,
I get a flow of X, which is slow and way below what it should be.
If I open the hot, I get the same exact slow flow. If I open them
both, I still get exactly the same slow flow, ie no improvement.

To me that's weird, because it implies that there is some obstruction
after the two valves. But this is a Grohe faucet from 25 years ago,
ie it's not one with a tempering valve or anything fancy, so I
would assume the water just comes from each valve into a simple T
and is combined. So, I'm at a loss as to what could be wrong.
If it were debris, I could see it lodging before or in a valve,
but how could there be anything after the two valves?

Water pressure into the separate bathtub is fine, plenty of
water flow there, many times what's coming out of the shower.
Only other odd behavior is that the cold side of the sink,
which is also a Grohe, once in awhile with the faucet wide open
or near wide open, there will be little or no flow. But close
it once or couple times, and the problem goes away.

I haven't take the faucets apart yet, I guess that's a next step,
but have been reluctant because I didn't know how the handles
come off. Just found on the internet that they just pull off.
So, I can investigate that way or alternatively I thought about
rigging up my air compressor and blowing back into the shower
line.

Any ideas?

Try taking the screen head off and jambing a small snake or such. I had the same issue and snaked a yard of coax. It did the job even though it should not. It was a free sug and worked.

Thanks to you and Dean for that idea. Coax sounds like the perfect
thing. I'll give that a try if reverse blowing with air doesn't work.
I went to Lowes yesterday and got a reducing elbow to make the air
to pipe connection.

Also Gfre says it may have an anti-scald in there, which AFAIK, it
doesn't. It's actually ~32 years old and I've been there for 20+
years, I've had the shower on full hot occasionally and never saw
anything cut in to prevent full hot water from coming out. I
suppose it could have been fouled up all along and only now is
showing this new system, but I tend to doubt it.

I'm not to keen on trying to take the stem out. I finally found
a video showing how that type of Grohe faucet handle comes off.
It just pulls off, no screw. Which tells me I'm screwed. A regular
handle with a screw is a bitch to get off after a couple decades.
One that only relies on being pressed on to hold it must fit even
tighter. Chances of getting that off without damage is probably
zippo.