I've got a Delta 1700 series shower, and it's been running out of hot water more quickly over the past few months. Had a plumber come by, and he recommended replacement of the water heater (in retrospect, without specifically checking the issue with the shower, given that other faucets worked fine), but installing a new 40 gallon heater hasn't solved the problem. Had the plumber come back, and he said that the problem was with the valve cartridge, which he quoted for a $500 replacement. After some searching on here and elsewhere, I figured this was the right diagnosis and that it was an easy enough replacement to do on my own.

However, when I called Delta to arrange getting the replacement part under warranty, the Delta representative was convinced that it couldn't be the cartridge, since (in his words) a faulty cartridge would result in no water coming out, and not just a lack of hot water. He didn't offer any further advice other than to remove the cartridge and see if it rattles, which would indicate a working pressure balance spool. What do you think? Is he right? Everything I've seen elsewhere points to it being the cartridge. And if it's not the cartridge or the heater, what could it be?

And if it's not the cartridge or the heater, what could it be? I'm with Delta on this. Your plumber was wrong to lay the blame on the shower cartridge.
Let's find out where we're losing the hot water. Filling a lavatory and sink takes much less volume then your shower. Try this. Run your shower on just hot water and note the time it runs out. Now do the same with the bathtub. If it takes about the same amount of time then that puts the focus on the water heater. Let me know what you come up there and we'll go from there. Even if it is the heater you don't need a new one. 500 bucks to simply replace a cartridge? Fire your greedy plumber and bring in someone with more scruples. Let me know about the hot water. Back to you, Tom

Thanks, Tom. This makes sense, and good advice. And sorry for the delay in replying. In any case, I've run both the shower and the bathtub on two separate days in order to ensure that both tests were working off a full tank. The shower runs out of hot water around 11 minutes (with the water starting to get cool around 9 minutes), and the bathtub runs out of water around 9 minutes (with the water starting to get cool around 8 minutes). So, it sounds like that puts the focus on the hot water heater?

Two additional items that might be of use: (1) when the plumber first came to look at the shower, he left it such that it would only get tepid at the hottest. I had to have them come back right away, and it turned out that the first plumber had turned the scald guard pretty far down. I had the second guy turn it up, but it still seems like the hottest isn't as hot as before, but it's fine for me. (2) In running these tests, I've noticed that the bathroom sink actually won't run fully hot water afterward, which is different than what I'd found before. Maybe it's due to fully using the hot water, and perhaps that puts even more focus on the heater. What do you think about next steps?

Hi Tom,

What do you think I should do as a next step? If the cartridge isn't the issue, is there something I can do to adjust the heater?

Thanks again,

Adam