Just plane weird.

[Eagle & Bear]

I have renovated every system in our 29' 1976 Airstream and used the trailer extensively over the past 15 years. There were things that needed work right away and I got to other components when I had time.

The freshwater system was in need of replacement. There were striations with copper oxide showing along the original copper waterline mounted below and inside the rear storage space hatch. I replaced all of the copper with Upanor PEX and installed a new pump 4 years ago. Everything functioned as it should...up until this past week.

As retirees do, we have been staying in the desert during the winter and using the pump to move water. Last week I went to take a shower. Since we had no shore hookups, I used the pump. When I started the shower, the warm water came through for a few seconds and then it turned really cold (I do not like taking a shower with cold water).

Wife was not using the sink. The water became warm and then cold again. Interestingly the warm water was on for 5 seconds and the cold water flowed out of the shower head for another 5 seconds. The pump switches on and off normally but the water pressure and temperature did not fluctuate when the pump cycled.

Using the pump, I can take a shower in warm water for 5 seconds and then I have to point the shower spray down until the water becomes warm again. Today we pulled into a place where we have shore water, sewage and electricity. After getting settled in, wife got into the shower. When she got out of the shower, she said that there was no incursion of cold water coming through the shower head. The water was warm the whole time she was using the shower.

Now that we are getting water from a central source, the water pressure does not fluctuate and stays warm throughout a shower. Good news but why does the shower water change from warm to cold and back to warm again in 5 second intervals.

[RFP]

It's the mixing valve on the back of the water heater. When they "stick" they produce exactly what you are describing. Sometimes just the jarring of driving down the road will un-stick the thing, sometimes a good whack with a hammer will do the trick. Disassembly and cleaning in vinegar or CLR may be needed, or even replacement. Try the hammer first.

[CBWELL]

If you replaced the original water heater with a modern one with the mixing valve, that could be your problem. If not, I would look at the shower valve itself. If it is the original Moen, then the cartridge possibly needs replacement The new shower valves are designed so that you will not get a shot of very hot water that could scald you. The pump itself could be the culprit as well, not providing as steady flow. When on city water if everything works fine, switch back to pump and see what happens. Let us know what the end result is!

[Fungus]

Water heater make and model?

[Wazbro]

Check your winterizing valves also, if you have a 3 valve bypass system you may have a valve in the wrong position.

[CBWELL]

Thinking about the problem again, and looking at all the variables, I believe the problem is the pump! Why? Well, from what I read, you were boondocking and everything worked fine... until it started to cycle hot/cold/hot/cold. Hooked to city water and everything good. What changed? Valves didn't move by themselves on the water heater. Valve in shower didn't change. Only two things changed! Water supply, and with city water, pressure remains almost constant unless major draw such as a major fire and the FD using tremendous amount of water. Pumping from water tank, you are using a different system to supply pressure. I don't believe that your trailer has a pressure tank. The supply to the two different systems, hot side and cold side, do not come off a common manifold. Water will go the path of least resistance. The only variable in this problem is the supply of pressure. City water pressure, or pump pressure! Shut off the city water and try the pump from tank. If problem occurs, the culprit is the pump.

[Eagle & Bear]

Thank you all for your responses. The water heater (HWH) is a 10 gallon Atwood. It has a production date of 1/2014. I installed it about 6 years ago but never knew that they have some kind of mixing valve.

It has been a year since I've drained the HWH so that has to be done. When this HWH dies I plan on installing a propane demand HWH. We have been using what appears to be the original Delta shower faucet but recently purchased a "balance valve" that I will be installing in the next month or so.

The Delta "balance valve" is not what I expected. It looks like they use nothing more than a small orifice on both the cold and hot water inlets to restrict the flow so that someone in the shower does not feel the immediate shock of cold water when someone turns on the sink faucet.

[ROBERT CROSS]

Originally Posted by Eagle & Bear

Thank you all for your responses. The water heater (HWH) is a 10 gallon Atwood. It has a production date of 1/2014. I installed it about 6 years ago but never knew that they have some kind of mixing valve.

It has been a year since I've drained the HWH so that has to be done. When this HWH dies I plan on installing a propane demand HWH. We have been using what appears to be the original Delta shower faucet but recently purchased a "balance valve" that I will be installing in the next month or so.

The Delta "balance valve" is not what I expected. It looks like they use nothing more than a small orifice on both the cold and hot water inlets to restrict the flow so that someone in the shower does not feel the immediate shock of cold water when someone turns on the sink faucet.

Your year doesn't have a 'mixing' valve.
From my experience...as noted above, make sure the winterization valves are set properly, then get a new high flow water pump.

Bob
🇺🇸

[Steamguy]

Originally Posted by Eagle & Bear

... The water heater (HWH) is a 10 gallon Atwood....

I can solve your mystery!

I recognize the model, I had one. Typically those water heaters come from the factory with a check valve on the output, which has a spring in it. When flow drops below a certain rate, the spring forces the check valve closed.

When you're operating off the water pump, the flow rate will slow to the point that the check valve closes, cutting off the hot supply - and bam, cold water in the shower.

How I know for sure:
We had a great old SOB before the Airstream, and this was the case when you used the 'button' on the showerhead to cut the water. Except it didn't cut the water flow all the way off. The check valve in the water heater closes, so no hot water moves at all. The shower nozzle hose fills with cold water only, you use the 'button' to turn the water back on, and SURPRISE!!

How I fixed it:
I never winterized by using the pink stuff and bypassing the water heater (which is what the check valve and bypass valve are for), so I took the pipe off the check valve fitting, and drove a screwdriver into the fitting, punching the little spring-loaded ball through into the water heater's tank. Presto, no more shots of cold water when showering.

I always drained the system at the low-point drains (easily accessible from inside - hear THAT, Airstream??) and drained the water heater from the outside.

Hope that helps.

[Eagle & Bear]

Emptied the HWH. Not much debris. Spent a week boondocking. Water temp in the shower never fluctuated. Maybe it was the rocky dirt track that knocked something loose. Looking forward to installing the balance faucet and a demand HWH.

[Boxite]

Originally Posted by Eagle & Bear

Emptied the HWH. Not much debris. Spent a week boondocking. Water temp in the shower never fluctuated. Maybe it was the rocky dirt track that knocked something loose. Looking forward to installing the balance faucet and a demand HWH.

A demand water-heater is not all roses either. The one I installed (admittedly not in an AS) wastes plenty of water before the cold water is sufficiently-heated…then when the flow is stopped….and subsequently restarted…a blast os SCALDing water is first-delievered. (the water flow stopped turns the heater off…but the plumbing inside the heater, still being hot, over-heats the now static water…and now is waiting for you to ask for more water so it Scalds first….then delivers sub-desired cooler water…then begins to bring the heat-again…. just as you stop the flow again… an endlessly disappointing result. This cycle doesn’t occur when not boondocking and if hooked up to city water because water-thrift isn’t so necessary to cause that cycle.)