Regulating Hot Water Temperature and Aquastat ?!?

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FMcCracken

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I manage 4 townhouses which have identical plumbing systems/ layouts. So, if a problem comes up in one unit, there's a good chance that it's bound to come up in the others. This solution can potentially be applied to each of the 4 townhouses, which are only 5 years old.

One client is telling me that the Master shower works great, regardless of how long they shower. They have never run out of hot water when showering. However, the Master tub - notsomuch. The hot water comes out of the tub faucet at 120* for the first 1/2 minute. Then gradually lowers to 110* during the second minute and then before the second minute is over, the temperature reduces further to 100*. If the tub hot water is turned off for a minute, the water comes out at 120* (after a few seconds) when turned back on.

The hot water tank is set to just south of Scald and a mixing valve (Taco 5000Series) tempers the hot water to 130*, shown on the in-line temperature gauge.

When the tub begins filling (3rd Flr, hence the initial temperature drop), the water temperature at the Taco mixer, reduces to the same temperature as tub spout - 120*. After 5 minutes of running, the water temperature maintains at 95*-100* - at the mixing valve and tub.

There is a Honeywell Aquastat L4006A unit which regulates a hot water circulation pump, installed on the return side. The hot water return mixes with the cold water supply that feeds the Taco mixing valve to further extend the hot water capacity. Currently, the aquastat is broken, so the pump runs 24/7. We are going to replace the aquastat and the mixing valve and install temperature gauges on each the hot and cold water supplies to compliment the existing tempered feed.

A. Should we add/ install a mixing valve where the hot water return meets the cold water supply feeding the primary/ existing mixing valve to better control the water temperature/ differential at the valve?

B. Which model Honeywell/ Resideo aquastat is best for this type of installation? There are High Limit, Low Limit, High and Low Limit units. What should the differential be?

C. The current mixing valve temperature was set when water was not being used. If it is set while water is being used, the initial hot water coming out of all taps is way too hot.

D. Any ideas on how to better regulate the hot water temperature coming out of the tub faucet and sink faucets? The shower has a thermostatic showerbody so that "should" be a no brainer.

How water tank and boiler (Ultra 3) are Weil-McLain

Frankie
 
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jadnashua

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Do you have a dedicated return line, or are you using the cold water line for the return?

Is there a check valve on the return line so water can't be drawn through both the return line and the hot?

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FMcCracken

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Do you have a dedicated return line, or are you using the cold water line for the return?

Is there a check valve on the return line so water can't be drawn through both the return line and the hot?

I've been avoiding the site for a bit since Terry has amped up his ads, and I've used an Ad blocker for years...the alerts are annoying, almost as bad as the ads.

There is a dedicated return line. Return line mixes with the cold water feed before it returns to the HWH.
Circulation pump works.
No check valve on return line prior to the cold water connection.
New aquastat installed - Johnson/ Penn A421. Sweet unit. I have set a cut-in at 100* and a cut-out at 110*.

In this configuration, the cold water supply chills the hot water return. Somehow it overcomes the circulation pump and downward return pressure.

Plumber then installed a return branch from the return line to the HW supply line, after the mixing valve but before the thermostat. This way the water no longer returns to the tank.

A) No check valve on return line is a problem (because it creates a pressure imbalance) and cold water starts to flow upstream of the return line - UNLESS the hot water is being used. If it's being used, the water at the tap becomes increasingly hotter, perhaps because it's being fed by the supply AND return line - the return line not having a tempering valve.

Plumber refuses to install the check valve because he doesn't think the cost in time (water heater needs to be drained, but a drain spigot was never installed lower than mid height of tank) warrants the result. (Head explodes)

B) Plumber's solution: Piping the return so it bypasses the HWH and feeds directly to the supply line, after the supply tempering valve This means the circulation pump will run indefinitely when homeowner is away, since the water will cool to room temperature without any influx of hot water. The only time the water will stay hot is when it is in use. Warm-up time at 3rd floor tub is 30 seconds. Not ideal but acceptable (by homeowner).

C) Seems there's no point in having a return line using the existing configuration.

Your thoughts?

Frankie
 

jadnashua

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Water takes the path of least resistance. Without a check valve on the return line, you can get water drawn from both the hot side and the return side.

With a dedicated return line, you might be able to put the check valve nearly anywhere in the line. That should not require draining the WH, just turning the water supply off. Some check valves require a specific orientation, and that may limit where it is installed.
 

Fitter30

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Return line needs a check. Depends on water quality if it's a few years old might need to have the guts replaced or soak in vinegar to remove lime deposits which slows its modulation.
 

Master Plumber Mark

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Return line needs a check. Depends on water quality if it's a few years old might need to have the guts replaced or soak in vinegar to remove lime deposits which slows its modulation.


I totally agree.... at least this is where you should start out is with a swing check valve.....

are you filling a normal tub or is this a whirlpool tub that cannot be filled totally>>>???
 
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