My single lever Delta valve when turned on works fine on cold water, but as I proceed to hot (full turn) it will rumble until it loses all pressure At full hot the pressure is reduced greatly, and rumbles. It seems the hot water is not working properly. The only way to use the shower is on the cold setting. I replaced the 6" pipe out of the wall and the shower head. I have a Weil-Mclain tankless boiler, five years old with a round mixture valve which may be the problem, I can't tell. I also took the Delta valve apart, removed the cylinder (mixture control ??) and it was clean and looked fine. Put it together and still have the same problem. All other plumbing in the house, including another shower with the same Delta fitting work fine. It is just this one shower valve that does not work. Is it a problem from the tankless unit, the valve, or what?
Help.

If it's not effecting any other faucets then most likly it's the mixing or antiscald valve to the shower.

How long have you had that shower valve and has it always been like that?

If it's not a new valve, but the problem with the hot water has just recently occured, I would check for an obstruction in the hot water pipe going to that shower valve. If you can, turn the hot water off to that bathroom, take out that mixing cylinder again and hold a pail over the valve body while a helper opens the hot water shut off valve to the bathroom for a few seconds. Try and get that shut off valve wide open to get full flow through the pipe before closing it again. Afterward, check the pail to see if anything came out of that hot water pipe.

This message has been edited. Last edited by: Nestor,

Did what joecaption and nestor suggested. Bot a new Delta balancing spool which looked exactly like the original. However, could not seat it all the way in, just a fraction off and no way to go any further. I put the old spool back, which look good. Re-check the hot water pipe from boiler to shower, although quite long, maybe 50 feet secured it tightly to avoid movement. Did what joecaption suggested and took the spool out and ran the water to flush any junk. All was clear and I got a bath. Can't figure this one out, doesn't seem to be anything left to do. Guess I'll have to call a plumber. Unfortunately, to replace the entire faucet would be difficult as there is a small opening through my fiberglass shower. The sweated joints, hot and cold water are not very accessible. Not much thought given to replacing the faucet when the original was put in - 1981. Thanks to both of you.

Can you replace the faucet by opening up the wall BEHIND that faucet? That is, can you replace the faucet from the back rather than from the front? Plumbers don't care about how someone else is going to replace that faucet 35 years down the road. Only homeowners concern themselves with stuff like that, cuz they know it might be them that has to do it.

If push comes to shove, both Delta and Moen make X-tra large excutcheons so that if you have to replace a shower faucet from the front, you can use an extra large escutcheon to cover the large hole in your wall. Delta's escutcheon is 13 inches wide by 8 1/2 inches tall and goes by the part number RP29827, and you can see a picture of it here:

http://i.ebayimg.com/t/DELTA-R...OBN1nKsMvOw~~0_3.JPG

The round escutcheon on the Delta shower faucet fits the 5 1/4 inch diameter hole in the RP29827.

Moen's equivalents, the M1920 and M1921, are of similar size and design, but you can get them in a fake gold finish, too.

http://www.plumbersurplus.com/...-rw-55191-334576.jpg

http://www.plumbersurplus.com/...rw-101577-280349.jpg

http://www.moen.ca/shared/imag...o_weblarge/m1921.jpg

So, in both cases, if push comes to shove, you can always just use a bigger escutcheon over your bigger hole.

This message has been edited. Last edited by: Nestor,

It was the balancing spool, but the first one I purchased was no good, but the second one works fine. Now the plumbing supply does not want to take the first one back because it was used, and can't be resold, no consideration to the fact that it did not fit and could never be sold. Anyway, thanks very much to all that helped me thru this ordeal.

You need to think faster. How could it be "used" or even "installed" if it couldn't be fully inserted into the faucet body in the first place? The best you can say is that you tried to install it but couldn't, and so you certainly couldn't have "used" it either.

But, don't throw that first balancing spool away! As a factory defect, it's valuable to Delta.

Quality control is actually a sub-field of Industrial Engineering. Typically a company will use the math of statistics to figure out how many products to check and how often to check that many to ensure that the average rate of defective products leaving the factory is less than some arbitrary number; 1 in 10,000 for example. But, as the sources and causes of defects are uncovered and corrected, the frequency of defects becomes progressively smaller, and that makes those few remaining factory defects progressively more valuable to the manufacturer. That's because they can tell him where problems in the manufacturing process are either still cropping up, or are starting to crop up.

You should find out who your local sales representative or sales agency is for Delta faucets and bring them that defective balancing spool. I fully expect Delta will refund your money in exchange for it... if they can tell it was originally defective and wasn't just damaged.

The problem is that you're talking to a sales clerk or at best the sales manager of a small plumbing parts supplier. They figure they're just upholding company policy and protecting their customer base from people returning used or damaged goods and them putting them back into stock for resale. And, there's good reasoning behind that company policy too.

But, I expect you'll get a much different response from Delta if you give them that defective product. If they can tell it was defective when it was shipped, I'd be surprised if they didn't give you some kind of a cash refund.

PS:
Delta is a subsidiary of the MASCO corporation. MASCO also owns such other well known manufacturing companies as:
1. Price Phister, Waltec, Peerless faucets, BrassCraft Products
2. Weiser Locks
3. Behr Paint, MasterChem (who make KILZ Sealer)
4. Arrow Fasteners
5. Mills Pride Cabinets
http://masco.com/about/our-companies/

This message has been edited. Last edited by: Nestor,