Just bought 3 years old 5bedroom house. Master bathroom has 2 sinks, shower and bathtub. However, bathtub will get only lookwarm out of the faucet even with only hot water on (has separate cold and hot water knobs) while shower and sinks are scalding hot. I assume the same hot water line serves both the shower and bath which are adjacent. And I believe the hot water heaters work together so both provide hot water to whole house. Can't figure out why this would be happening. Any ideas?

What's a diverter / cartridge? How does that work? The tub and shower are completely separate.

The problem with the above video is it has a single knob while mine has separate hot and cold knobs.

Gigem_94 said:

---

What's a diverter / cartridge? How does that work? The tub and shower are completely separate.

The problem with the above video is it has a single knob while mine has separate hot and cold knobs.

---

Post a pic of yours...

This. Our tub in Master bath has a mixing valve located under one of the vanities.

I thought it might be something like this but for the life of me I can't find it. Any idea where it could be besides under a vanity? And there are no access panels to get to the plumbing except for one in the master closet to a shut off valve.

Is the tub on an exterior wall? Could have an access panel on the outside of the house. I know that sounds crazy, but that's where it is at my parent's house.

Here's a picture of mine under the sink if that's of any help. Sorry for the crappy picture quality.

Also....I've watched the builder in our neighborhood put this inside the tub enclosure in a few houses with no access because they don't give a damn. Mine is only under the sink because I made them move it there during rough-in. Our neighbors would have to pull the tub to access it.

You could also check the attic if applicable.

Gigem_94 said:

---

What's a diverter / cartridge? How does that work? The tub and shower are completely separate.

The problem with the above video is it has a single knob while mine has separate hot and cold knobs.

---

If you turn on just the hot water, are you getting the same pressure as the cold? Same flow rate?

Either way, I'd check the hot water cartridge/stem. You can do this by removing the hot water handle. How you remove the cartridge/stem depends on the faucet, but it shouldn't be difficult. It's either held in by a retaining nut of some kind or screwed in. Pull it, clean/replace it, put it back in, and then see how it goes.

Asked the previous owner and he didn't know anything either.

No valves on exterior walls.

Concern is what poster above said - builder encapsulated valve behind the tile with no access.

You could try to prove there's a mixer valve somewhere by shutting off the cold water supply to the tub. You mentioned a shutoff in the closet.

Instead of adjusting my mixer valve I thought I'd be smart and just turn off the cold supply going to the mixer valve. That way only hot water was going to it. That worked great for about 30 seconds until the water got hot enough.....and the mixer valve closes off completely. Just a tiny trickle of water would come out.

So if you do have a mixer valve hidden somewhere and you can shut off the cold supply to the bathroom and run hot only at the tub....this could potentially prove a mixer valve exists.

You can also turn off the hot at the heater and it will stay cold.

Bumping this thread because I'm currently having this exact same problem, and I'm at a loss.

I've even opened up the wall in the closed to expose all of the bathtub faucet piping, and there is no mixing valve or scald protector.

The hot water handle cartridge is only one year old, and I had hot water like three days ago at the tub.

Any suggestions?

Following this thread too.

My master shower has a two handle Pfister pfaucet, and there must be a hidden scald protector or mixing valve I can't access.

If I turn on the hot water at a sink, the shower water heats up fine, but otherwise it's generally tepid.

Since we continue to design plumbing access panels for tubs (not showers) due to CODEs past, this news led me to the new CODE IRC 2021 = College Station adaptions where I find insanity in only requiring access to temperature diverter valves or whirlpool pumps.

So if your problem is a diverter valve mis-adjusted, it would not have passed city inspection without an access panel - it says. Location usually behind the faucets but other locations possible if an afterthought.

Asking for a Master Plumber visit would satisfy our inquiring minds that need to know ..... hoping it's not a leak or crimped hose.

Potcake said:

---

This. Our tub in Master bath has a mixing valve located under one of the vanities.

---

same here. Blew my mind.