Replacing Mixing Valve in a 2018 Tab 320-CS

JP2558

Hot water performance been lacking, turn it on and it lasts about 30 seconds then goes lukewarm. Tested setting the adjustment to maximum hot and it's no better. All valves are properly set. Consensus is to replace the mixing valve. I ordered a new one from a dealer last October however I'm just getting to install it now. What the dealer sent is an Alde TMV with the red cap however it isn't an exact replacement for what is came with the Tab. See pictures. Can I use the TMV or do I need to source an exact replacement? And if I can use the TMV how would I go about disconnecting the existing hoses and connect them to the TMV? Anyone with any insight?

Thank you!

pthomas745

The bad news is: the LK550 mixing valve (the one with the Black Cap) hardly ever failed, so the info about replacing it is scarce.

Reading over the Facebook pages, the new Thermostatic valves are failing at a pretty constant rate.  And, it is hard to tell on your photo, but that valve doesn't look quite like the others we have in the trailers.....but it could just be the photo itself.

On the new valves, there are "push fittings" on each of the fittings that will just disconnect. Look over this thread.

https://tab-rv.vanillacommunity.com/discussion/13395/hot-water-problems-thermostatic-mixing-valve-2021-tab-400 

rfuss928

It's possible the problem is clogged inlet filter screens similar to the ALDE mixing valve issues.  I have no knowledge of LK550 or its internals but removal and inspection may reveal it can be cleaned and put back in service. 
I've serviced my ALDE tempering valve twice because of clogged screens.

This thread shows examples of the ALDE valve with clogged inlet screens.
https://tab-rv.vanillacommunity.com/discussion/comment/207752#Comment_207752

JP2558

Thanks for the input. The TMV package received has a label Alde Item No. 3102003 on it. But hopefully upon removal of the old one I can remove the screen and clean it. 

Bayliss

@JP2558, here's another discussion (short) to look at:

https://tab-rv.vanillacommunity.com/discussion/13243/low-hot-water-pressure-with-new-speedfit-thermostatic-mixing-valve#latest 

JP2558

@Bayliss - Thanks. I clean the water filter screen every year during winterization.

JP2558

So I uninstalled the LK550 and completely disassembled it and I did not find a screen anywhere within it. From looking at other threads it appears to not have one so I have all the parts soaking in a white vinegar bath. I guess we will see how it performs after the vinegar bath.

MuttonChops

JP2558 said:
. . . LK550 and completely disassembled
. . . did not find a screen anywhere within it.

I also took my LK550 apart yesterday, yes - - no screen.
nüCamp suggests the Coarse Temperature Adjustment Cap (my name) . . . the one under the +/- top black cap/cover . . . should be set to be level with the brass housing, as 'cap' has a limited depth of threads and backing it out more (to increase hot water) could cause the spring to pop the guts out.

On my unit I've adjusted it so much that half of the 'cap' threads were above the housing.  When I fully removed the 'cap' nothing happened.  It seems the lower plastic part, Cold Water Valve (my name) and the spring were jammed down in the add, add cold water position - - - or that's my guess.  It took some time to loosen and then remove the Cold Water Valve.

With it apart I've:
  A) tested the thermostatic actuator.  Measured piston position at room temperature and after placing that item in boiling water . . . . it works.
  B] tried to teach myself how the 550 mixer works and believe I've got the basic theory of operation.
  C) Have attempted to identify the correct part number O-Rings.  As they are not local HW store standards I'll skip replacing them for now.
  D) like many others I searched and searched for the LK 683 Repair Kit but couldn't find any.

Here's my Theory of Operation:


And a Parts List:


Reinstalling and testing mine without replacing anything will be done at a later date.

JP2558

@MuttonChops - Nice research and documentation! I'm going test mine later today and will post results.

JP2558

"When I fully removed the 'cap' nothing happened.  It seems the lower plastic part, Cold Water Valve (my name) and the spring were jammed down in the add, add cold water position - - - or that's my guess"

Same with mine.

But before I test I'm am also going to boil the thermostat actuator. Then I will  boil the spring and the naked valve itself. My reason is that upon reinstalling the spring and the plastic spring support, I found it to be difficult for the spring to easily move. I will clean the plastic with alcohol to see if it can move freely.

Update - it appears the thermostat actuator is working after boiling. And the spring is now moving as expected!  This is encouraging!

I also set the "Coarse Temperature Adjustment Cap (my name)" to be level with the brass housing. Question? What is the result recommended setting in relation to the hot/cold mix? Just wondering as it relates to how I reinstall the +/- knob for maximizing hot water additional adjustment.

JP2558

Got everything installed but I encountered a leak. At first it was gushing as soon as I turned the pump on. After sopping up the water, I showed my wife where it was leaking. See circled area in photo. After we pushed the water intake up into the mixing valve and jiggled everything, we retested and there was only a minor drip coming from where the water intake actually connects to the mixing valve (where I disconnected it).

Now I'm perplexed as to whether the plumbing will hold or will it resume gushing after a few miles on the road jostle it around for a bit.

So my new question is how would I remove and re-fit the circled area? I'm a true novice at plumbing, especially using all these plastic fittings.

MuttonChops

On Topic but not related to most recent comments/question.

Believe I have located the Thermostatic Element manufacturer (in China of course) I've sent their 'info' page a request for retail suppliers.

The Legom LG004X 'wax thermostatic Element'.

So we are getting nearer to creating a Repair Kit Parts List since no one can locate the LK 683 Repair Kit.  Of course the 'return spring' is a critical part and I've no idea at this time how to reverse engineer that.

While searching for the element came across several articles noting that these Thermostatic Mixing Valves require regular service/maintenance . . . . with Key Notes Being:

a]  Replace worn O-rings {leaks related} and
b]  Re-install with Plumbers Grease to aid the seals and up/down motion.

I suspect many folks are replacing the entire (pricey) Mixing Valve when a cleaning and service would resolve the common operation issues.  After all the valve is only being used a small percentage of its lifetime cycles in an RV - - but it does get a huge amount of vibration and dry (winter) wet (summer) cycles.

BridgerSunset

It may be helpful to look into John Guest Speedfit info on the John Guest website.  Parts & FAQ's & other info.     The fittings are fairly simplistic, but seem to be pretty forgiving after removing & reinserting a few times.

pthomas745

This link goes to a thread that has the same basic discussion of what this little "adapter" is and how it works. This basically "adapts" the two different pex sizes, the one from the mixing valve, and the pex lines in the trailer.  It may be you are missing a clip there where the two fittings connect.  There are a couple of these "push fittings" in the trailer.

https://tab-rv.vanillacommunity.com/discussion/17541/disconnecting-the-water-lines-from-my-alde

In that thread, there is another linked thread that goes to a conversation about these fittings and how they work.  The pertinent comments are toward the bottom of the thread.

This is the second thread>

https://tab-rv.vanillacommunity.com/discussion/12008/leaking-pipe-under-the-bed-any-ideas/p1

JP2558

@pthomas745 Thanks for the disconnecting the water lines link. That picture shows two red clips on the assembly, neither of which I have, for both cold and hot. From what I gather those should assist with the leak I experienced yesterday. However we've never had any leaks over the last six years so I'm perplexed by their necessity.

MuttonChops

@JP2558;
Success !    I've got Normal Hot Water Operation after Mixing Valve Maintenance.

Thanks for inspiring me to do something.

Fluids; water-plumbing,  oil-hydraulics, fuel-diesel/gas are my DIY demon

After re-assembling the LK550 Mixing Valve (with plumbers grease) my rig now has usable Hot Water again . . . . should have done this maintenance before a recent 5-weeks adventure.

For some time I've had the classic Mixing Valve Issue of a short burst of hot water then cold water.  As noted earlier (like yourself) I found the LK550 Mixing Valve Cold Water Valve jammed in the add as much cold water as possible position.; i.e. jammed in extreme down position.

After cleaning the internal parts on first re-assembly the Cold Water Valve was moving but had sidewall resistance.  Plumbers Grease was applied to the Cold Valve 'top section' that contacts the brass barrel.  Grease was also placed on both ends of the compression Spring.

With Grease the Cold Water Valve moves very smoothly.  [ to the finger tip the barrel feels smooth, a scope camera provides a rougher surface image.  I could not think of a way to clean/smooth the barrel . . so just used grease ]

When the Hot Water response starts to degrade (again) I'll just re-grease the parts.

Side Note:
     When Alde Service Panel stated water temperature at 124F  ( 25-minutes after cold start )
     I could fill sink 5/8 full before warm water was felt.  A huge improvement over the Blast of
    hot then cold operation.

     When Adle reports water temperature above 140F [5/31 edit] ( 40 minutes or so operation on full electric heating )
     I could fill the sink full and the water was still very warm if not hot.

That is wonderful. As my usage generally is washing dishes using a pot full of hot, and taking "sea showers"

{ x USCG Coastie after all ]

I'm Happy.

JP2558

@MuttonChops That's great to hear. Tomorrow I will be doing the same with regards to using the plumbers grease. Stay tuned!

pthomas745

@MuttonChops @JP2558 An owner on one of the FB pages has a new LK550 in hand, and it wondering about how it connects to the fitting there at the bracket,  Their photo is below:

The question was:   "But now that i removed the broken one im wondering if where i screw the black fitting it look like on the regulator side its supposed to have an O-ring can you confirm that please?"

And this: "its the black plastic fitting that they gave me under the bracket.. do i have to put teflon tape or dope before reinstalling or is there supposed to havesn o-ring or gasket between the fitting and the brass". 

Any ideas on how this should go back together?

MuttonChops

pthomas745 said:
. . .  An owner on one of the FB pages has a new LK550 in hand,

@pthomas745; from the one picture that appears to be an Alde Speedfit TMV; Case-Acme HG110-HX due to the HEX Shaped deposits on the top surface .  I for one have no knowledge/experience with that model.

Ask FB Post Person . . . what color was the plastic cap - - Red is HG110,  Black is LK550.

Then you can search for Speedfit, etc.

Jpvert

MuttonChops said:

pthomas745 said:
. . .  An owner on one of the FB pages has a new LK550 in hand,

@pthomas745; from the one picture that appears to be an Alde Speedfit TMV; Case-Acme HG110-HX due to the HEX Shaped deposits on the top surface .  I for one have no knowledge/experience with that model.

Ask FB Post Person . . . what color was the plastic cap - - Red is HG110,  Black is LK550.

Then you can search for Speedfit, etc.

Im the one who asked the question on FB. I have the LK550.

pthomas745

@MuttonChops this was the original photo he showed.  

MuttonChops

@Jpvert, @pthomas745

I've not worked on the cold connection so have no knowledge to share,  sorry.

Jpvert

MuttonChops said:

@Jpvert, @pthomas745

I've not worked on the cold connection so have no knowledge to share,  sorry.

Did they have gasket on the hot side connection? Im pretty sure all 3 connections are the same. If you have worked on it did you put something on the thread to be sure its not leaking?

MuttonChops

Jpvert said:
Did they have gasket on the hot side connection?

I do not know, maybe @JP2558 or Pex links @pthomas745 provided can answer.

JP2558

Quick update: We spent three days boondocking last week (yes under the heat dome Saturday and Sunday), and am glad to report that our hot water problem has been solved! Thanks to everyone who helped me resolve this issue by teaching me how to disassemble, test, and rebuild our original mixing valve. Plumbers grease is our new friend!