Hot water issues

Hi, I am having trouble getting hot water to my furthest bathroom. I am currently having my 2 other bathrooms redone and they had to shut off the water multiple times. I figured this messed with my water heater and it crapped out. (it was 18 years old). So I installed a new water heater and I'm getting scorching hot water in the kitchen and garage. In the problem bathroom, the sinks get pretty hot but the shower only gets luke warm at best. Now if im in the shower and my wife flushes the toilet, it becomes scorching until the toilet is done filling and then the shower goes back to luke warm. A plumber suggested going to a 3/4" gas line and he was pretty confident that was my issue but there was no improvement from what I can tell. We had zero issues before we started the bathroom remodel. They only installed new shower valves. Is there something they could have messed up? Sorry for the long post, I'm just beyond lost. Does anyone have any suggestions.

Thanks,
Jarred

You need to get a plumber that knows what he is doing in there to check things out. I would have no idea what they cut into and changed. I can assure you changing the gas line size will do nothing. Sounds like you have a old shower diverter with no pressure balance on it which would prevent the scald from the toilet flush. You may have cold water mixing into the hot side on one of your faucets. You may need to look into a recirc line. Your shower should have a temp adjustment that you can make to allow more hot water.

How old is the house, how old is the shower valve in question here?

Post a pic of the whole shower valve and trim and handle.

The shower valve might be gunked up with sediment.

Or it might be pressure balancing type, and the balancing spool or module is stuck or gummed up with crud.

Might just need a new cartridge, or could need more than that.

Jeff Handy said:

How old is the house, how old is the shower valve in question here?

Post a pic of the whole shower valve and trim and handle.

The shower valve might be gunked up with sediment.

Or it might be pressure balancing type, and the balancing spool or module is stuck or gummed up with crud.

Might just need a new cartridge, or could need more than that.

Click to expand...

Mid 60s house, the valve could very well be original. I attached a photo. Its an old Moen. Another thing I noticed is that the his/her sinks (in the same bathroom) get hotter when both are running. If I shut one off the temp drops considerably. Cold water must be getting introduced somewhere. The renovation guys just installed new shower valves in my other 2 bathrooms. One of the bathrooms literally shares a wall to my problem shower. I am unable to test that bathroom because it is not complete yet.

Is it possible to mess up a valve job that would create this issue?

Thanks

CT18 said:

You need to get a plumber that knows what he is doing in there to check things out. I would have no idea what they cut into and changed. I can assure you changing the gas line size will do nothing. Sounds like you have a old shower diverter with no pressure balance on it which would prevent the scald from the toilet flush. You may have cold water mixing into the hot side on one of your faucets. You may need to look into a recirc line. Your shower should have a temp adjustment that you can make to allow more hot water.

Click to expand...

Thanks for the reply. Is it possible to mess up a valve install that would give me these issues? I feel like cold water is getting introduced somewhere. Because when the toilet pulls cold water my shower gets hot. I noticed the sinks in the same bathroom get hotter when both are running but if you turn one off the temp drops.

Sorry to repeat myself I am new here and I wasn't sure how this site attaches my replies.

I think that's a moen shower valve it's possible they crossed the lines if the are back to back those chrome flat head screws shut off the water to the hot or cold ,shut off the cold on both showers then turn the showers on see what temps you get them try there sinks also
And see what happens

Geofd said:

I think that's a moen shower valve it's possible they crossed the lines if the are back to back those chrome flat head screws shut off the water to the hot or cold ,shut off the cold on both showers then turn the showers on see what temps you get them try there sinks also
And see what happens

Click to expand...

It is an old Moen valve. I can't test anything in the other bathroom because it's being remodeled.

There’s your cross connection, when they put the cartridge in you’ll be back to normal

Lots of possible issues here.

First of all, in your old shower valve, that big vertical slot is where there is a pressure balance cartridge that might have gone bad.

And also, any and of all your sink faucets might be passing hot or cold water, even when turned off.
If they are single handle type.

The easiest test is to just change the sink valve cartridges.

And Geofd was right, pipes might have been hooked up bass ackwards in the remodeling.

I was typing while Rickyman was posting, did not mean to step on any toes there.

His theory is good also.

https://www.moen.com/shared/docs/exploded-parts-views/3170pt.pdf
The Moentrol balancing spool can be seen in this diagram.

Rickyman said:

There’s your cross connection, when they put the cartridge in you’ll be back to normal View attachment 25958

Click to expand...

It didn't dawn on me that the cartridge hasn't been installed. Its gonna suck when I realize I tossed a 18 year old water heater over this. But I do hope thats the issue thanks for the reply.

18 year old water heater was about 6 years past a common failure age anyway, good riddance to it.

Jeff Handy said:

18 year old water heater was about 6 years past a common failure age anyway, good riddance to it.

Click to expand...

Yeah true. It sure was a champ tho. I'll update as they finish these bathrooms. They have about a week before my baby shows up. Thanks for everyone help.

sLackuR said:

It didn't dawn on me that the cartridge hasn't been installed. Its gonna suck when I realize I tossed a 18 year old water heater over this. But I do hope thats the issue thanks for the reply.

Click to expand...

Keep us posted

Any update?

You called it, once they installed the cartridge everything was back to normal. Sorry we had a baby 3 days after posting and I still dont know which way is up

Thanks to everyone that replied.