What's the point of the hot water bypass?

[BobJones]

Hi Folks!

I'm looking at putting in a thermostatic mixing valve on the outlet of the hot water tank. At present, there is a hot water tank bypass lever in there and it leaks on one of the fittings. It doesn't matter what I do to seal it, it will leak.

My question is, just what is that hot water tank bypass valve there for?

I'm thinking, why not remove it when I install the thermostatic mixing valve and address the leaks at the same time.

[Old-Biscuit]

Bypass is for Bypassing the WH Tank when 'winterizing' RV so you do not pump Anti-freeze into WH Tank
Also WH could be removed for service by using bypass provided the WH Tank was installed with 3 valves (cold inlet/Bypass/Hot outlet)

Thermostatic Mixing valve....
Neat concept to control Hot Output temp.
Atwood has that system on their XT Models and many folks complain of Failures (no hot) due to mixing valve hot inlet becoming clogged with scale/calcium
RV water heater volumes are so small that the scale/calcium can be an real issue...unlike residential WHs were all of that crud falls to bottom of tank and is rarely carried up/out the hot dip tube
RV WHs Hot dip tube is NOT very far from bottom of tank and the in rush of cold water can stir up the crud and send it up/out the hot dip tube

Just something to think about and RESEARCH RV Water Heater Mixing Valve issues.

[BobJones]

Thanks Biscuit !!

Excellent. I never winterize the unit. Any time we put it away we used compressed air. So the loss of the bypass valve won't be an issue and it will get rid of several connections, one of which always leaks. Although, the addition of a thermostatic valve will probably add those connections back in

I was thinking the same thing about the valves - that they would be sensitive to all the sediment from the tank. I often have chunks up at the screens of the taps.

I saw that all the better valves have screens in them. This causes me to wonder.....maybe the smart play would be to install some kind of regular filter on the outlet of the hot water tank before the valve?

Not sure what to use but I bet even an automotive fuel filter could work. I would not be interested in treating the water, just filtering it while not restricting the flow and, ideally, using the screw on pex fittings.

The mixing valve I would be using would be a more 'industrial' type. Something that's typically used in residential or commercial applications.

Something like this;

[jacwjames]

Bob,
When we built a new house I tried to make it as energy efficient as possible so one thing I did was install at tankless hot water heater. After a short while my started to complain about lack of flow out of the faucets. We have hard water and the water heater was causing a lot of scale and since there wasn't a tank it would just push it to the faucets.

I ended up installing a fine mesh screen sediment filter (200 mesh) that catches most of the scale, I have to empty it about every 3 weeks. Although I didn't do it I could attached a timed valve that would purge the filter. When I was researching you have to use one for hot water. Here is what I installed


https://www.freshwatersystems.com/pr...13250741927979

[lenny-shawna]

Biscuit is correct. Plus I would use the bypass when I clean my water lines and fresh water holding tank with bleach.

[DutchmenSpor]

Here's the problem with mixing valves and why I hate them.

A mixing valve will always mix a certain percentage of water from the hot side and a certain percentage of water from the cold side. They do not regulate temperature, unless you get something that has electronics and a computer circuit board to keep the temperature consistent, if something like that exists.

What that means is, in the colder season when the water is COLDER coming into the camper, you are still getting (let's say a 50/50 mix) of hot and cold, same as when the outside temperature is hot in the Summer.

What does that mean? Let's take the example of 50/50 mix.

Water temperature entering the camper is 45 degrees (it's cold outside). The water heater heats to 110 degrees.

Mix the two at the mixer .... 45 + 110 divided by 2 equals 67.5 degrees when it leaves the mixer (No mention of the cool down as it runs through you water lines now.)

Now, lets say the outside temperature is 85 degree and the incoming water is 80 degrees.

80 + 110 divided by 2 equals 95 degrees.

And you can't make it any hotter in the winter. You're going to freeze your tushie when you take a shower!

I do not know how these mixers are set, but I do know, that in my current camper, the shower has a mixer and I hate the thing.

Because, when we want hot water in April and November, it's barely lukewarm at all our best efforts.

My shower handle is a single handle. I REALLY wish it was 2 knobs.

So, I pulled the handle fixture out of the wall, and reversed the pipes. Now, when I first turn on the faucet, it starts out all hot and the more you turn it, it cools down, opposite of the way it was installed. We now have nice WARM showers, even in November.

[Old-Biscuit]

Atwood uses a 160*F T-stat and Mixing Valve controls to 130*F hot out
When not clogging up it does a pretty good job at maintaining that 130*F output

When it clogs.......cold water and that can be a surprise when showering
Doesn't matter if one like Atwood is used or an 'Industrial' type used...scale/calcium/crud will clog them up requiring removal/cleaning ---soaking in vinegar etc or replacement

Suburban uses a 130*F T-stat.
End user controls/adjusts temp at faucet


BOB
WHY the addition of a mixing valve?

[BobJones]

@jacwjames - thank you very much for that link. That saved me a lot of research. I have no problem dumping the sediment from time to time.

@DutchmenSpor - you can adjust them. At least, 'normal' ones can be adjusted. If it came with your RV they might have tried to make it tamper-proof. They do adjust the temperature, they have to, because otherwise how would it reach your desired temperature?

@Old-Biscuit - what I've been wanting to do is run the tank at a higher temperature to increase the amount of hot water available.

As it stands right now, I've got it hot enough to scald your hands when filling the sink etc. I'd like to address that. I really would like to be able to dial in the temperature and then just put the hot on and not worry about it. Whether in the shower or the sink. But ultimately, I would prefer to run the tank at a hotter temperature for more volume.

[Old-Biscuit]

Bob
How did you crank up the temp hot enough to scald??

DYI....the Atwood Mixing Valve IS adjustable. Preset for 130*F Out and sealed at factory. Goo can be removed to allow access to allen set screw so one could engage the gears and change out temp setting
Atwood Mixing Valve has a 'screen' and screws directly into nipple on WH Tank

The XT Models also use a 160*F T-stat.....same button snap disc as standard 140*F T-stat except it uses a PIN post on one of the terminals vs a spade connector


Your 2000 vintage WH uses 2 separate sets of T-stats
One 12VDC set in outside compartment for the propane
One 120VAC set on the backside with the electric element

No higher temp setting for the 120VAC normal temp t-stat
140*F is standard

[super_rep]

Originally Posted by jacwjames

Bob,
When we built a new house I tried to make it as energy efficient as possible so one thing I did was install at tankless hot water heater. After a short while my started to complain about lack of flow out of the faucets.

https://www.freshwatersystems.com/pr...13250741927979

You should look into installing a water softener. They are especially recommended if you have the tankless type water heaters. The coils go in these heaters in hard water and tend to easily scale up. If you don't like soft water, just install it on the inlet to the water heater and not the whole system.

[BobJones]

Originally Posted by Old-Biscuit

Bob
How did you crank up the temp hot enough to scald??

I replace all 4 of the sensors and then direct wired the power feed so that it's not going through the switch on the side.

To be clear though, it's typically scalding when I'm running both gas and electric.

@jacwjames - I think that sediment filter is a good idea regardless. It would save me from opening the aerators on the taps and cleaning out al the chunks