Very low hot water pressure solved

krsmes · July 2023

After getting my T@B400 back from nuCamp with a replaced ALDE boiler (separate story https://tab-rv.vanillacommunity.com/discussion/17138/alde-unit-seeping-all-its-antifreeze-onto-the-floor) I was testing everything out and had practically no hot water pressure. I’ve taken care of every other (beside ALDE corrosion) repair myself so set out to figure this one out.

Turns out the thermostatic mixing valve intake screen was clogged.

It is in the blue circle above. Disconnected and took it out, cleaned it out as best I could (and ordered a new one $130) and put it back together — full hot water pressure. Almost as good as the cold water pressure which hasn’t been true for the past over a year.

So then the question is “why was it clogged?” The water is all through a filter, the pump has a filter on it, etc. And what I cleaned out of it was little black pieces of plastic or rubber. Working backwards through the system the next piece (yellow circle) is the one way valve. I unscrewed it and took it out and the insides of it fell out (should not be possible with disassembling the mechanism) and the black plastic connector itself was flaking apart inside.

My only guess is that it cannot handle the heat. Seems unlikely to me but not sure why it would be flaking off plastic like that after 2.5 years. This small section of pipe between the ALDE and the mixing valve (green outline in the picture above) has super heated water in it (145-165 degrees Fahrenheit, check your service menu on the ALDE panel with it set to hot water boost). This was confirmed with a temperature check on that red pipe.

The mixing valve brings in cold water to bring the temperature down to <120 degrees (depending on what it is set to) before going through the rest of the trailers pipes.

I found a nice brass replacement on Amazon for <$8 (Valterra P23415LF 1/2" Lead-Free Check Valve https://a.co/d/6Z2PDv7) that is a perfect drop in replacement fit. It has a similar looking internal white plastic mechanism but I don’t think that is what failed — the black plastic housing pipe of the old valve itself was disintegrating. I may consider replacing the two plastic ½” threaded pex adapters on either side with brass ones as well— the one on the ALDE side of the connector is discolored (powdery white).

Waiting to see if this might also fix my strange intermittent water pump turning on for 1 second randomly— possibly related to the failed one-way valve.

krsmes · July 2023

Waiting to see if this might also fix my strange intermittent water pump turning on for 1 second randomly

It did not

Basil48192 · July 2023

Thank you for this! I'm always looking for preventative maintenance issues to avoid a breakdown!

vhollow · July 2023

I too thank you. I haven’t had the low hot water pressure yet on my 2018 400, but your posting will be so helpful if I do. Yours is the type of posting that for me makes browsing the forum worthwhile.

dsfdogs · July 2023

@krsmes thank you for posting this as I too have low hot water pressure. Plus on my recent trip, twice the water pump turned on for a second, waking me up.

You replaced the thermostatic mixing valve? Do you think that was necessary once you cleaned the screen? And from whom did you purchase it?

Thank you,

krsmes · July 2023

@dsfdogs I bought the replacement from Truma directly but only to have on hand for my long (4-6 month) winter trips to the middle of nowhere in the southwest. Cleaning and blowing it out with air did the job for now

krsmes · July 2023

Just had my first shower while out on a test run weekend (dry camping)… I’ve never had this high of hot water pressure (or this hot) in the 2.5 yrs of owning this trailer. I wonder how long I had check valve disintegration and thermostatic mixing valve clogging issues.

ChrisFix · July 2023

krsmes said:

Waiting to see if this might also fix my strange intermittent water pump turning on for 1 second randomly— possibly related to the failed one-way valve.

My water pump has started to have intermittent 1 second bursts as well...Just started on our last trip in June. I'd love to hear if the replacement check valve fixes that for you. It's a reasonable diagnosis...I've not been able to find any external leaks that would explain the water pump cycling.

krsmes · July 2023

@ChrisFix no, not completely. I should have been more scientific about measuring the problem before but it seems to be much less frequent now.

Sounds like a similar problem, no leaks anywhere. Wondering if the pump itself is slowly falling and letting the some water go backwards back into the tank.

ChrisFix · July 2023

@krsmes
Oh well...it was a good thought! I guess we'll both see where this leads over time...
Funny thing...My mixing valve stopped working as well on that same trip the pump starting the random 1 second cycling. I took the valve apart and wiped off some minor corrision, and it has worked fine since.
The pump turns on/off via a pressure switch - perhaps that is the culprit.

Edit:
Found this article with this tidbit:
https://www.thervgeeks.com/rv-water-pump-pulsing/#:~:text=Your RV's water pump uses,of water pumps are adjustable.
"Also, as the pump ages, sometimes the tension of the spring changes, and a small adjustment can make the difference between a pulsing or non-pulsing water pump."

krsmes · July 2023

That is helpful info. I was already considering an accumulator tank add on for longer pump life (we dry camping a lot), but will try the adjustment in the meantime.

The nautilus diagrams https://tab-rv.vanillacommunity.com/discussion/comment/103939/ show another check valve between the pump output and the nautilus, I’ll have to look for it next time I have it apart. Don’t see it in the pic above. Might be built in to the back of the nautilus.

Denny16 · July 2023

Nice find. We have a Jan 2018 built TaB400, taken lots of hot showers, never had the chad, valve fail, or reduced hot water flow. My guess is the check valv failed, or was not the correct part for hot water use.
cheers

pthomas745 · July 2023

There was a report on this a couple of years ago. @krsmes was this the filter you found inside your valve?

https://tab-rv.vanillacommunity.com/discussion/13243/low-hot-water-pressure-with-new-speedfit-thermostatic-mixing-valve/p1?new=1

manyman297 · July 2023

@pthomas745 I too experienced low pressure but realized it was do to my pressure regulator...BUT I did clean out the mixing valve and it helped. It's a really quick and easy thing to do and probably something that should be done annually. But it also sounds like @krsmes had pieces of plastic from the fitting further upstream in her filter which I imagine would completely suffocate the flow.

krsmes · July 2023

@pthomas745 yes that was it but black flakes instead of whatever that white stuff was.

krsmes · July 2023

ChrisFix said:

@krsmes
Oh well...it was a good thought! I guess we'll both see where this leads over time...

Out on a week long trip now and the intermittent pump issue appears to be gone.

dsfdogs · January 2024

@krsmes, how did you remove the three connections (hot/cold/output) to the thermostatic mixing valve? I read they are speedfit connections, so do you press the white "ring" towards the mixing valve while also pulling out the black plastic elbow/connection?

Thank you,

krsmes · February 2024

dsfdogs said: do you press the white "ring" towards the mixing valve while also pulling out the black plastic elbow/connection?

Yes, exactly this.

AndreO · February 2024

Great info, very insightful problem solving! I'll be adding this to my list of preventative maintenance. Thanks.

sjensen98104 · April 6

Big thanks for posting this. Upon de-winterizing this Spring, my hot water was down to a trickle. After finding your post, I removed mixing valve, and looked at the valve's input screens. The hot water screen was packed with black plastic flakes. Never would have figured this out on my own. Have replacement brass check valve ($11) on the way. Ready for the season.

Very low hot water pressure solved

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