Low water pressure on bathtub faucet

[ZYouL8R]

We just moved into a house that is 27 years old. The water pressure is fine throughout the house except for the guest bathroom bathtub. It takes about 15 minutes to fill the tub up 2/3 of the way. It has individual knobs for the hot and cold water and the weird thing is that when you turn one on all the way, then turn on the other all the way, the water pressure does not increase. Basically, the pressure is the same whether only one is turned on or both. Both the hot and cold are working independently and one side doesn't have better pressure than the other. I took off the faucet and there was a little build up, but nothing crazy. The sinks in the same bathroom have great pressure. Any ideas on what could be causing this?

[Country cracker]

Sounds like it may have a separate valve somewhere that is not fully open.

[ZYouL8R]

I found a access panel in the closet that was cut at some point to access the bathtub pipes. I didn't see anything abnormal. There wasn't a valve anywhere in there either. Any other suggestions? Is there usually a valve for bathtub lines?

[fordracing19]

Does it happen to have an aerator on it?

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[Country cracker]

For my house I have a main box in the garage that has valves for every single line in my house.

[Lone Sailor]

Sounds like one or both of the valves is not opening all the way. Have you pulled the stems?

[2000 vert]

Do u know for sure that the faucet is a tub filler? They are different. I made the mistake a few years ago when I remodeled my bathroom. I took back the new faucet and got the much more exspensive one made for tubs and it solved the problem.

[ZYouL8R]

Do u know for sure that the faucet is a tub filler? They are different. I made the mistake a few years ago when I remodeled my bathroom. I took back the new faucet and got the much more exspensive one made for tubs and it solved the problem.

I'm assuming this is a tub filler, it looks like any other tub faucet I've ever seen. Here's a pic with the faucet and one of the handles removed and the water at its highest pressure. I'm not a plumbing expert by any means so I'm not sure what I should be looking for. BTW, don't mind the dirt, we just moved in.

[fordracing19]

Looks like its running good to me.

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[ZYouL8R]

Looks like its running good to me.

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I've never had a tub take 15 minutes to fill up 2/3 of the way to the overflow drain. Like I said, if I turn on the hot all the way, then turn on the cold all the way, the pressure does not increase. The max pressure occurs when only one side is turned all the way up. This can't be normal.