It is a Valley single handle shower valve. A similar Valley model (with possibly the same internals) is shown at
How likely is it that replacing only the cartridge will fix the low hot water flow problem?
How likely is it that the entire assembly needs replacement (requiring soldering et cetera)?
Hot water flow in the two other faucets in the house (kitchen and bathroom basin) seems fine.
How is the cold water flow at that shower?
IDK, good question. Cartridges can cause leaks, but I don't see a failure mechanism where they result in low flow. It seems more likely there is some debris lodged in there. Taking it apart, flowing some water, might fix it. Or if you have an air compressor, rigging that up to blow air backwards can work. Had a low flow problem here and that did it. I blew it backwards, from shower to bathtub. Nothing visible came out, no debris, but it fixed it.
I once replaced a 20-year-old shower valve (Harcroft) for that same reason. Once the new valve was in use and working well, I got the old one on the bench and found a rubber washer jammed in the hot water circuit. If I could have seen that before ripping it out, I could have saved a lot of $ and sweat!
99% of the time this is a stuck balancing valve and you can fix it by replacing the cartridge. I have taken the cartridge apart and fixed them but it is a pain in the ass and it might end up leaking afterwards.
Thank you for the input Micky, trader_4, croy and grfe. The cold water flow is fine. My condo requires a licensed plumber to do this repair (else the condo association will not shut off the water to do the repair). Today the plumber found the cartridge's hot water side clogged with debris. A new cartridge fixed the low flow. :)
A decent resolution.
Thanks for getting back to us.
I wonder if an air compressor would have saved a plumber's bill.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.