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 Lukewarm bath water/hot shower water
Author: nickarjuna (RI)

Hi all, I'm a new homeowner and am looking for a bit of plumbing advice. I have a Symmons Temptrol bath and shower fixture that looks exactly like this:


I've recently noticed that while the water coming out of our shower head is plenty hot, the bath water never gets better than lukewarm (and I've run it for many minutes). I've already tinkered with the limiter screw with no effect.

I've very little plumbing experience, so any advice would be much appreciated. What could be causing such a noticeable temperature differential between the bath spigot and the shower head?

After looking at some YouTube videos and information online, it looks relatively straightforward to replace the spindle assembly and/or the diverter. Would one of these components be the likely culprit?

Thanks in advance for any help!

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 Re: Lukewarm bath water/hot shower water
Author: steve (CA)

What type of water heater do you have? With the shower turned on to hot, turn on all other hot faucets and see if the shower turns lukewarm.

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 Thanks for the response :grin:
Author: nickarjuna (RI)

Hi Steve, thanks for the response. We have a tankless dual-purpose gas water heater. So, I turned on the shower (was hot), then turned on the 3 other hot water faucets in our house in addition to the running dishwasher. The shower water did indeed turn lukewarm.

Interestingly, though, earlier today I turned off the heat in the house (we use hot water baseboard heat) to see if the problem was that we were asking too much of the tankless heater. I left it off for 15-ish minutes, then ran the shower and bath. Shower was hot, bath was still lukewarm. No other taps were on at the time.

But are you thinking the problem is that the bath is over-taxing the water heater?



Edited 1 times.

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 Re: Lukewarm bath water/hot shower water
Author: steve (CA)

Yes. If the incoming water is colder than usual, that can also be part of the problem.

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 Re: Lukewarm bath water/hot shower water
Author: Stoopalini (TX)

Your tankless heater cannot keep up with the flow demand of the bath tub faucet. The shower is probably flowing somewhere around 2.5 gallons per minute (GPM), while the tub could flow 5 or even 6 GPM. Bathtubs faucets flow a lot more than sink or showers to fill the tub faster.

Tankless heaters are rated to raise the temp of the incoming water, given the flow and temp of the incoming water. So if the incoming water temp is say 50*F, and the tankless heater can raise the water temp by say 60*F with 2.5 gallons flowing, the result is 110* water. As the flow increases, the temp rises drops. So when you turn on the tub, and if the flow increases to 5 gallons per minute, the temp rise way drop to say 30*F Which would result in water temp of 80*F.

Now I don't know what tankless heater you have, or what your incoming water temps is, so I just made those numbers up as an example.

The easiest fix to this is to open the bathtub faucet up partially when filling the tub. It will take longer to fill the tub, but will reduce the GPM flow and enable the tankless to heat the water up to your desired temperature.

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 Re: Lukewarm bath water/hot shower water
Author: nickarjuna (RI)

Thanks for the responses steve and stoopalini. Yeah, our tankless is rated at 2.71 GPM, so if there really is that much of a GPM differential between the bath and the shower faucet that makes sense.

Sorry for the dumb question, but, if the shower and bath are both provided by the same hot and cold inlet pipes, how is it that the GPMs are so different? Does the shower head limit the flow by that much?

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 Re: Lukewarm bath water/hot shower water
Author: Stoopalini (TX)

Yes, the shower head is limiting the GPM. Your plumbing can deliver significantly more GPM than any one fixture could deliver. If that was not true, you wouldn't be able to have the shower, washing machine, sinks, tub, etc... all on at the same time.

Oh, and your tankless should have a performance chart. The 2.71gpm rating doesn't really mean anything without knowing what the temp rise is at that GPM. The literature should have a chart showing the temp rise at given GPM ratings. These usually go from 1gpm to 6 or 7gpm, showing the temp rise capability of the heater at each interval.

Then to determine what your outlet temp would be, measure the ground water temp by running a cold faucet and sticking a thermometer into the water flow.



Edited 1 times.

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 Thank you! Appreciate the helpful responses :cheers:
Author: nickarjuna (RI)

Will do, thank you! Appreciate the helpful responses.



Edited 1 times.

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 Re: Lukewarm bath water/hot shower water
Author: packy (MA)

possibly a good flushing might help ?
[www.google.com]
otherwise just run the tub fill slower by moving the diverter lever slightly towards the center.

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