Wednesday, December 7, 2022


RV Doctor: Why is there no pressure in RV fresh water plumbing system?


Dear Gary,
The water pressure in our motorhome is getting lower and lower in the bathroom, plus it makes a whistling sound when the hot water is running. The sound seems to be coming from or near the water heater.

I have replaced the connector and pressure valve where you hook it to city water. It still has low pressure in the bathroom; especially the hot water has very low pressure. Any help would be appreciated! —Billy

Dear Billy,
Here are a couple of things to check. Remove the faucet strainer at the outlet of that bathroom faucet set. It simply unscrews from the outlet. There may also be a flow restrictor component inside, depending on the brand of faucet used in your motorhome. A flow diverter may also be present — usually a white plastic piece with holes in it. It basically directs the output flow to a certain pattern.

Be sure all the components in the tap outlet are clean and free from all obstructions. It’s common for mineral deposits to accumulate in this strainer assembly. It’s possible that significant flow restriction at the faucet would cause back pressure at the water heater. As an annual procedure, it’s also a good measure to perform this simple maintenance task at every faucet in the RV.

Additionally, some faucet assemblies have removable stems for both the hot and cold faucet valves. In some cases, these can be removed for cleaning. Again, it depends on which brand the manufacturer originally installed.

Your situation could also be caused by an issue originating at the rear of the water heater. Gain access to the rear of the heater from inside the RV. You’ll probably see a set of bypass valves used for winterizing. First check the valves themselves. You will either have a one-, two- or three-valve setup that allows you to bypass the water heater for winterizing purposes. Be sure the bypass valves are in the correct position and that the appropriate valves are either fully opened or fully closed.

There should also be a check valve at the cold water inlet to the water heater. The cold inlet is the bottom-most fitting. The check valve is a one-way backflow preventer that allows cold water in and prevents the heated water from migrating out of the water heater back into the cold piping system. It’s possible the check valve is partially open; again, mineral deposits can prevent the spring inside from closing off the valve completely. This is probably the source of the whistling noise you hear.

You can obtain a new check valve at your local RV accessory store or on It will attach with common pipe threads. Be sure to obtain the correct size. You will have to drain the water heater in order to remove the cold water line plumbed to that check valve fitting. Flush out the water heater as you drain it. There are aftermarket hose attachments available to aid in this process. This will help eliminate those pesky mineral deposits that can migrate to the faucets.

When installing the new check valve, apply a pipe thread sealant approved for fresh water systems to the male threads and carefully thread the new valve into the heater, taking care not to cross-thread it! Then simply re-attach the cold water inlet tubing to the new valve, apply water pressure to refill the heater and check for leaks. You’ll know the water heater is filled when you have free flowing water from each hot faucet in the motorhome. It may take a minute or so of running to rid the system of air, but this should eliminate any blockages and that whistling noise.

gary-736Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.



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Awana Black
2 years ago

Thank you so much!!!!! Just the fix…the check valve.

3 years ago

You could also choose to simply take the core out of the check valve in question. That would eliminate the need to address the problem again in the future. I’ve done this and I’ve never had a problem of this sort again.

Tim Bear
3 years ago

Wow! Poor Barbie! Even she got a lemon RV. Too bad Mattel doesn’t make a Chuck Woodbury doll to go with Ken & his friends.

Joe Bulger
3 years ago

My bathroom sink had a very low flow, when I took it apart I found at least 5 screams in it. I reassembled it with 1 and all is fine.

LTC (ret) Skip Trafford
5 years ago

Dear Gary
There is a mischievous ghost living within my Southwinds fresh water pumping system! From time to time, my pump seems to die and will not turn on at all. However, when I open the rear compartment and access the outdoor sink and pump valves and “fiddle” with the shower hose head and/or the hot and cold faucet handles, the pump suddenly starts pumping. This exercise sometimes takes a full day of “fiddling” before the water pressure/pump starts working again. Any idea what the problem is? Is this common? Should I purchase a new faucet and shower hose/head system to exorcise the poltergeist?
Thank you

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