No hot in tub but hot in shower

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LilBit

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So I live in a mobile home and I've been here for 2 years. I noticed this issue when I first moved in but didn't know how to fix it. I never take baths here since it isn't a full bathtub so it's never really been a major concern but it is irritating and I've been wanting to fix it so now onto the issue...

I have hot water throughout the house without issue except in the bathrooms. I get hot water out of both showers with no problems. They get full pressure as well. However when I run water out of the tub spout the cold runs perfectly fine and you can even get it about halfway with some luke warm water but if I turn either bathroom past a certain point or to all hot water the water drops significantly and no hot water seems to be coming out. There is also thumping that happens in the walls which I'm assuming is the pipes. I've tried looking online without anything really being similar to the issue I'm having. I don't really know where to start looking to solve this issue.
 

Weekend Handyman

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I am not a pro.

I am confused about what you are asking.

Is the unit with the issue a tub/shower? Are you saying the unit in question will give you hot water out of the shower head but not out of the tub spout? If both were not giving you hot water, I would suspect the cartridge.
 

LilBit

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I am not a pro.

I am confused about what you are asking.

Is the unit with the issue a tub/shower? Are you saying the unit in question will give you hot water out of the shower head but not out of the tub spout? If both were not giving you hot water, I would suspect the cartridge.
Yes this is correct. It is a tub shower unit. I can get hot water from the shower but when I try to run the hot water from the tub spout it runs for maybe 30 seconds then sounds like it starts knocking the pipes in the walls until the water is shut off or switched back to the shower. If I run the cold water through the tub spout it doesn't do that. It runs like normal.
 

LilBit

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Mobile homes have some odd things about them. What does the water heater look like? How old?
It is a standard water heater. I'm not sure of the exact age of it but I don't think it's that old. It looked relatively clean and I've lived there for 2 years so it's at least that old.
 

Weekend Handyman

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Yes this is correct. It is a tub shower unit. I can get hot water from the shower but when I try to run the hot water from the tub spout it runs for maybe 30 seconds then sounds like it starts knocking the pipes in the walls until the water is shut off or switched back to the shower. If I run the cold water through the tub spout it doesn't do that. It runs like normal.

Again, I am not a plumber.

I would try changing the cartridge in the valve.
 

Weekend Handyman

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If it was the cartridge I shouldn't be able to get hot in the shower either. It wouldn't work in either.
I am not sure about that … you might or might not be right.

Is it the same kind of valve in both places. If so, you could try switching the cartridges and see if it changes anything. If it does not address the situation, at least you will have eliminated one potential cause.
 

LilBit

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I am not sure about that … you might or might not be right.

Is it the same kind of valve in both places. If so, you could try switching the cartridges and see if it changes anything. If it does not address the situation, at least you will have eliminated one potential cause.
The cartridge is in the handle that adjusts the water temperature. The water for both the tub and shower would use the same cartridge because it's a combination tub/shower.
 

LilBit

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So an update...my roommate broke the handle in the spare bathroom. I had a plumber come fix it. They replaced both the handle and the spout. They also had to cut into the back to access everything. Not sure if they had to cut out pipe pieces or not but it did solve the knocking issue in that bathroom. Now when the tub runs in there it doesn't do that at all. Only my shower now does. So my plan is to just do the same in that bathroom and hopefully no more issue. I'm guessing it's the spout that is the actual issue. I don't think the hot water can get through because the water pressure drops drastically as well once the knocking starts and the hot water is trying to come out. This is all just guesswork, to be honest, but hopefully no more issue.
 

Tuttles Revenge

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The symptoms to me sound like a tankless / on demand water heater where the low flow shower head is fine but the tub spout is asking for more hot than the water heater can produce and instead of slowing the flow, the heater just gives up.. Even though its said to be a "normal" water heater, that doesn't tell us what it is or isn't.

It should be Impossible for a single tub/shower valve to have hot out of the showerhead but none out of the tub spout since the mixing control valve is one and the same.
 

John Gayewski

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The symptoms to me sound like a tankless / on demand water heater where the low flow shower head is fine but the tub spout is asking for more hot than the water heater can produce and instead of slowing the flow, the heater just gives up.. Even though its said to be a "normal" water heater, that doesn't tell us what it is or isn't.

It should be Impossible for a single tub/shower valve to have hot out of the showerhead but none out of the tub spout since the mixing control valve is one and the same.
Thermostatic valve gone bad? Closes with more flow? Doesn't sound like something I've encountered or could imagine.
 

LilBit

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The symptoms to me sound like a tankless / on demand water heater where the low flow shower head is fine but the tub spout is asking for more hot than the water heater can produce and instead of slowing the flow, the heater just gives up.. Even though its said to be a "normal" water heater, that doesn't tell us what it is or isn't.

It should be Impossible for a single tub/shower valve to have hot out of the showerhead but none out of the tub spout since the mixing control valve is one and the same.
It is not thankless. I have a tank water heater. If the tub was asking for more than it could be provided then I would be able to get some hot and then have it run out of hot water which isn't what's happening. I have absolutely no hot coming out of the tub spout. I can readily switch from tub to shower and get hot out of the shower each and every time I switch it but none at the tub. It begins to rattle pipes when it tries to. Like I said in previous posts I believe the issue was with either a section of pipe or the tub spout itself. I had to have the spare bathroom (which has the exact same tub, spout, and shower head) get the tub spout and handle replaced. After this there was no longer that issue in the bathroom.
 

John Gayewski

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It is not thankless. I have a tank water heater. If the tub was asking for more than it could be provided then I would be able to get some hot and then have it run out of hot water which isn't what's happening. I have absolutely no hot coming out of the tub spout. I can readily switch from tub to shower and get hot out of the shower each and every time I switch it but none at the tub. It begins to rattle pipes when it tries to. Like I said in previous posts I believe the issue was with either a section of pipe or the tub spout itself. I had to have the spare bathroom (which has the exact same tub, spout, and shower head) get the tub spout and handle replaced. After this there was no longer that issue in the bathroom.
Something with the diverter plugging the hot somehow.
 
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