Fix hot water spike in shower on toilet flush etc

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BrentP

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Hey everyone,

I have an older condo (1977) with newer showers (probably mid 90s) and when the toilet flush the hot water spikes. My research suggests that the newer cartridges would fix this. The current fixture is a Moen with what I assume is a 1200 series cartridge behind it. If this is the case can I fix my problem with a better faucet without changing out the rough in? Or am I out of luck?

Thanks!
 

Jeff Handy

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Out of luck.

You need to install a whole new shower valve, with a pressure balancing cartridge or module.

The plumber will need to open up the tile in your shower, unless you are lucky and there is easy access from behind, by cutting through the wall behind the existing valve.
 

bud16415

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Does it only do it when the toilet in that bathroom is flushed? Or if someone opens the kitchen sink will the hot in the shower spike?



If it is just the toilet I don’t know if this would work or not as a partial fix, but I wonder if slowing down the fill rate to the toilet would help. For most people they wouldn’t care if it took 1 minute or 5 minutes for the toilet to fill and if it were to keep someone safe in the shower it might be worth a try to close the toilet fill valve almost all the way down to slow the flow rate thus keeping the pressure up to the shower.



Again I have never tried this and @Jeff Handy might comment on the feasibility of doing this.

Also BrentP welcome to the forum. :welcome:
 

Jeff Handy

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Yes, partially closing the shutoff valve for the toilet might lessen the hot water scalding issue.

Sometimes, if the toilet tank fills very slowly, the flapper does not seat properly or reliably well.

Sometimes, the shutoffs get noisy or will whine if they are almost closed.

Valves that are partially closed tend to wear out internally.

As you suspected, it probably also happens with other fixtures in the house, but the OP can advise on that
 

BrentP

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Thanks for the welcome guys!

yah, that’s a bummer... the hot water spike will happen with other fixtures as well. I guess I was hoping that “universal “ rough ins from moen gave you some flexibility.. one shower will be easy to access, the other will not.
Thanks for confirming everyone. I appreciate it!
 

BrentP

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Would just replacing the cartridge potentially help? Or are those older cartridges just always going to do this?


Edit: I think the answer to this is a firm no :)
 
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BrentP

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Add on question on the same topic! Someone was taking a shower in the second shower and they complained that the showers went cold for “a few minutes” - I assume because someone else was taking a shower upstairs. If I had installed a Posi-Temp would the flow have just stopped until the hot water returned?

does this suggest a larger plumbing issue for water delivery?
 

Jeff Handy

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With a positemp valve or similar pressure balancing valve, the shower flow will slow down but not stop entirely, if hot or cold water is drawn somewhere else in the house.
 

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