Cleaning Delta brass shower/tub valve

Rookie/newbie question: is there a way to clean the third hole (mixed water out) in a Delta valve?

I get about 1 gpm flow with cartridge in; 7 gpm with cartridge out and water on. Delta has sent 4 cartridges but no improvement.

I've used hose fittings and garden hose with caps on tub shower stem in various combinations (cartridge in, cartridge out, water on, water off). I know there is no obstruction in pipe to tub spout, to shower head. I know water pours out of hot and cold holes in vale with cartridge out.

But water does not flow freely out of the third hole (mixed water out) when I attach garden hose on tub or shower stem and cap the other. (Back flushing.)

Delta insist the problem is a defective cartridge, but I'm now on my fourth one. Most of the agents do not seem to know there is a third hole in the valve. Am I crazy rookie or are they?

So is there a way to clean the third hole? I've tried wire, pipe cleaners, CLR.

Or do I have to hire a plumber and change the entire valve, cutting into walls or tile! Yikes!

Give us a little background on the problem (ongoing issue - just started). What type of piping do you have ?

Water flow to tub and shower slowed gradually over last year or two. Plumber put in new cartridge which did not improve things. Plumber thought there was some obstruction and tried to clean something, maybe pipes, maybe holes in valves...I don't know. I called Delta and they insisted that it was cartridge problem. 4th cartridge will arrive tomorrow, which would show they have quite a quality control problem.

I cut hole in wall behind bathroom and it is copper pipe, brass valve.

What other background info would be helpful?

Post a picture of the faucet you have with the trim removed. Delta had a faucet that the balancing spool was not part of the cartridge. If you should have that model the spool needs to be replaced.

Thanks for your replies.

I should have provided more background info: it's a Delta Monitor 1700 Series tub and shower fixture. It uses the Delta RP46463 MultiChoice Univ Pressure Balance Cart Assembly.

So I'm assuming that with the 4 replacement cartridges Delta has sent, pressure balance is not the problem. Correct?

What often happens when replacing the cartridge the rubber seals on the side of the cartridge tear and remain in the valve body closing off the water passages. Remove the cartridge and checkout the hot and cold passages on the sides of the valve body.

4th Delta cartridge arrived yesterday. Per Delta instructions, I removed all seals and springs in the valve and flushed the hot and cold lines, and then installed the new cartridge and the new Delta supplied seals and springs. No change.

When flushing the hot and cold lines, water just GUSHES out. No old rubber seals remain in the valve. I continue to think the problem is with the third hole which is for mixed water out, leading to the tub spout. Using garden hose connectors, I've tried to backflush the third hole, but water flows out at the rate of 1 gpm vs. 7 gpm when I flush the hot and cold lines.

So is there another way to clean the third (mixed water out) hole? We have well/hard water, so would CLR help? If it is mineral deposits, why wouldn't the hot and cold lines also be plugged?

Or is it time to replace the brass valve?

I was under the impression that you had a single lever faucet. Just what do you have? Can you post a picture so were all on the same page. Is it a two valve faucet or a three valve? If it's a three valve the problem may be the transfer valve.

Problem solved! I had a eureka moment!

I removed the tub spout, capped the stem. Then I held a small rubber hose up to the third hole of the valve, attached a funnel on the other end and poured in CLR. Most of it spilled out but enough got in. It sat there for about 30 minutes and when I took the cap off the tub stem, junk and gunk flowed out.

I put the cartridge back in, turned on the water and it is now flowing at the rate of 2.5 gpm vs. 1 gpm before. I probably will do this again and let it sit overnight to clean even more junk. And since we have well/hard water, maybe I need to do this once every five years or so.

So let's hear it for CLR! And simple solutions. Grateful that I don't have to tear out walls to replace valves.

You may have a steel nipple feeding the spout. If so I would change it to brass eliminating the problem.