Hot water problems - Thermostatic Mixing Valve - 2021 Tab 400

RockyRichard

When our 2024 TAB 400 came out of hibernation this spring, the hot water would get warm, but not hot. The water pressure in both City Water and Dry Camp modes is not noticeably different than it always has been. The glycol and water temperatures shown on the Setting Menu-Service are Normal: 147F Glycol, 144F Water; and Extra Hot: 163F Glycol, 151F Water; the Alde is doing a stellar job of heating everything to proper temperatures. The Glycol reservoir is full (at Max when cold) and the bleeders that are convienient to access have no appreciable air in them.

So I turned to the mixing valve adjustment. It hadn't been touched since we were delivered the trailer in December 2023. It was already set to the maximum (i.e., it wouldn't budge counterclockwise). But, it turned smoothly, but tightly, clockwise. So I measured water temps. Whether under Normal or Extra Hot settings, with the hex head screw fully counterclockwise, it is putting out 98F water out of the kitchen faucet. After reading numerous labyrinthine comments on the mixing valve, I elected to disassemble the valve to check for clogged filter screens, etc. An annotated photo of the disassembled valve is attached. Disassembly was relatively easy. I found some detritus on the screens but not enough to create a significant flow problem. So, I finally ceded DIY fix and bought a new valve from Airstream of Colorado, owned by Windish RV, our TAB dealer in Denver (Windish RV didn't have any in stock). $210 out the door. I installed the new valve, set at maximum (full counterclockwise), and was getting 130F water—scalding hot. 1 1/4 turns clockwise brought it down to 118-120. My assessment is that the thermostatic control assembly (see photo) failed; everything else on the valve seemed perfectly normal.

2024 TAB400 BC 2024 Subaru Ascent Premium Denver

pthomas745

These "thermostatic" valves that Alde provides are failing at prodigious rates. Thank you for the breakdown photo. And, 210 bucks for a mixing valve…is…robbery.

Rodent77

My problem is when just using hot water in Dry Camp mode, the pressure is fine when you turn it on and then when the pump kicks in the hot water drops to a very low flow. Cold is fine. I cleaned our the mixing valve and the problem still persists. Wonder if the valve is still shot or I have a different problem.. I will have to try this with water connected to trailer.

MuttonChops

@RockyRichard ; Welcome to the TAB Family.
Excellent first post, we've been waiting for someone to document the Adle Brand TMV.
Your picture is very logical and helpful.

= =

Did you consider:

1. Testing the Thermostatic Element and Piston Movement with a cold water to hot water test.
2. Lubricating the o-rings and spring with Plumbers Grease, older TMV spring is known to jam in cold position.

Those maintenance steps might have saved you $210 . . . maintenance is needed very few years.

MuttonChops

@Rodent77 said:

. . . using hot water in Dry Camp mode, the pressure is fine when you turn it on and then when the pump kicks in the hot water drops to a very low flow. Cold is fine.
. . . will have to try this with water connected to trailer.

Knowing how the Hot Pressure compares to Cold Pressure when on city-water will be a very helpful data point.

Until then, consider:

1. Double check winter by-pass valve is fully in the summer position.
2. Reset the Alde Tank 'air cushion' by dumping tank water via the Yellow Relief Valve. Adle manual recommends resetting the air cushion every ten days of continuous use and having 'tank' empty when trailer is between trips.

pthomas745

@MuttonChops Remember this mixing valve from a few weeks/months ago? It seems to be a very basic device…..and at only 35 dollars at Amazon, owners could save lots of time and hassle by simply tossing the "Alde approved" mixing valve. There is a failure of hot water per day over on the FB Nucamp pages due to faulty mixing valves. The Alde device is simply a failure waiting to happen.

There is a post here in the Forums where a 400 member replaced the "old" LK550 with this valve. I am basically plumbing illiterate, but it seems to me that: removing the "John Guest" push fittings, and crimping one of these 90 degree elbows (after we get the pex sizes straight) to the existing hoses/pex would allow a routine replacement from a big box store instead of the "searching for a dealer who can order parts". Am I on the right track here? How hard would this be to do as far as crimp tools, etc? (I've read over the pex crimp tool threads the last day or so). I believe the red pex hot water line coming from the Alde hot water tank is 12MM, or close to 1/2 inch. Not sure on the cold water pex lines, and some of them are even simple crimped hoses in some trailers.

Again, I have no idea if that elbow is the appropriate fitting.

I know the mixing valve works..but what should owners do to "plumb" it in the right way?