Tuesday, December 5, 2023


Potential problems with plastic bypass valves

RV Doctor

Dear Gary,
I own a 36-foot Holiday Rambler Ambassador. The day before we left on our last trip, the temperature here dipped to about 16 degrees so I kept the heater on in the coach and placed a small space heater in the bay where all the water lines are. The morning we left all was fine. I didn’t see any sign of freezing so away we went. We stopped about six hours into the trip when I noticed ice forming underneath the bay where the water lines are. (I have no way of heating down there while traveling.) Also we had no water pressure inside the coach.

When we stopped about three hours later the water pressure had returned and everything looked thawed. Upon our arrival at our destination, I did a more detailed inspection and found that the strainer basket part of the water pump had separated slightly from the water pump which caused a small leak. There was no damage to it so I simply reinstalled the part and there were no more leaks. The rest of the trip was uneventful.

When we returned I began to re-winterize the RV using a non-toxic RV antifreeze by disconnecting the supply line from the pump and using a tube in the bottle of antifreeze. I allow the pump to pull the antifreeze into the water lines of the coach, then I turn on each faucet until the pink stuff comes out. Before any of that, of course, the first thing I do is after draining the water from the system and water heater is put the water heater in the bypass mode.

After putting it in the bypass mode I noticed that the pump pulled all of the antifreeze out of the bottle before shutting off, so I checked to see if any of the faucets were in the open position – they were not. When I walked around to the other side of the coach I saw the antifreeze running out of the water heater (the drain plug was still out).

My question is, do these valves go bad? I disconnected the lines from the valve and using a flashlight looked into the valve as I would turn it from normal to bypass and it seemed to be working fine, but for some reason the antifreeze just kept going into the water heater. Can you tell me what may have happened? Did the freeze some how affect this? As far as I could tell we never had anything freezing inside the coach. Thanks for your help. —James

Dear James,
You certainly have the correct procedure down for traveling and winterizing during cold weather. I’m happy to hear you were able to enjoy your destination, at least, event-free.

As for the bypass system: Some plastic valves used in a few bypass kits can be prone to early demise due to the effects of cold and heat. I’ve not heard of any problems with brass valves in such applications, but the cheaper plastic ones worry me.

It’s plausible that the cold and heat extremes have damaged the seals inside the valves thereby rendering them inoperable. Warping or distorting of the plastic valve body may also contribute to a faulty valve. Perhaps even a bit of dirt or hard calcium particle migrated through the system into the valve and damaged the seal.

If your bypass valves are indeed made of plastic (I’m not sure which type Holiday Rambler uses), I would strongly suggest you replace them with brass valves. This should eliminate this from happening again.

Another possibility, though I doubt it happened, is that the valves were not fully closed during your re-winterization. You appear to be acutely aware of the process, so I would put my money on faulty valves.


Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.





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Steve (@guest_38766)
4 years ago

All of this brings up something I have wondered about. How do you travel, with a trailer/5th wheel in below freezing temps. My rig’s undercarriage is insulated, Arctic something or other package, but it is designed to have heater air flowing through to keep it warmed. I keep my fresh water to a minimum from home to destination. I put some RV anti-freeze in my gray/black water tanks, but what about the hot water, pump, and just water in the lines. I depart AZ for Colorado in November and return in in Mid-February.

Thanks, Steve

Ronnie Bolling (@guest_38635)
4 years ago

I’m just getting in to RVing so I’m no expert by far, but being a former automatic transmission rebuilder who is also an avid environmentalist, IMO the best way to winterize an RVs water system is to use an air compressor to blow out all the water; no toxic or semi-toxic chemicals are involved and this will 100% get rid of every drop of water if you follow the instructions with the kits that are designed to make it happen using low-pressure compressed air.

George (@guest_38648)
4 years ago
Reply to  Ronnie Bolling

I use compressed air to blow out the water lines but blowing it into the city water hookup does not evacuate water in your pump, strainer and connected lines. You need to pump RV antifreeze through the pump to protect it from freezing. And the last thing to do is add a cup of RV antifreeze to each of your P traps: sinks, showers and also the toilet. Don’t forget your outside shower if you have one.

Wolfe (@guest_38633)
4 years ago

Another possibility, affecting both plastic and brass valves, is the plastic *handle*… I’ve seen several valves where the valve seals are fine, but the handle can rotate without operating the actual valve. With the handle held on by a screw, it looks like it’s operating except the stem is not actually rotating. I’m assuming this happens when the valve is forced while partially frozen or maybe just stiff with calcium crud. Either way, you’ll generally have to replace the valve, but it’s another option for why it looks like it’s turning but water still passes.

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