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Ask Dave: Cold water runs in a trickle, but hot water runs fine. What gives?

Dear Dave,
Our cold RV water pressure at the kitchen sink is a trickle, both on city water and using our pump. The hot water pressure is fine. The shower and bathroom cold and hot water pressure are fine. What could be causing this problem? When we first purchased (new), the kitchen cold water pressure was tolerable but has steadily gotten worse over the years. Yes, we’ve cleaned out the faucet screen numerous times, which doesn’t account for the hot water flow being fine. —Chris, 2015 Nexus Viper 27

Dear Chris,
If the hot water flows out the faucet then it is not the screen as both hot and cold come to the faucet body and get mixed up through the head to the opening, as you suggested. There are not very many 2015 27-foot units coming up on the Google search to reference that type of floor plan and slides. But I did find a 27V, which should be close.

What I was looking for was where the kitchen sink was located and if it was in a slide room. I have found a few units that have gotten the plumbing pinched when they have faucets in a slide room. However, from what I can tell, yours is a fixed wall on the passenger side just back of the entrance door.

Check for RV water pressure obstructions

Since it is a low flow when connected to the city water pressure and the onboard pump, it has to be an obstruction in the cold water line somewhere between the faucet and the connection after the water pump. Your city water fill line bypasses the pump, but then the line coming from the pump connects to that line to supply water throughout the coach.

Typically these lines are ½-inch Cross-linked Polyethylene or PEX, which is a semi-rigid material but much more flexible than copper or the older PVC and CPVC used. The fittings can be either hard plastic that is crimped with a clamp ring or some type of compression fitting such as Flair-It™.

This is an illustration I have used several times showing the PEX and Flair-It used by Winnebago. Most manufacturers today are using a blue and red version of PEX to identify hot and cold. Here is an example of the colored PEX with clamp rings.

Check water lines if you're having trouble with RV water pressure
Check water lines if you’re having trouble with RV water pressure

You should be able to open the cabinet door under the sink and tell which type of plumbing you have. I would start by tracing the cold water line from the faucet down into the cabinet and following it as far as you can. Verify it is not bent or kinked along the way. It’s not unusual to load cabinets and storage compartments with your stuff and shove something against the line and have it pinch. You should be able to follow it down into the lower compartments all the way to the pump.

If the hose isn’t kinked…

If you can’t find a kinked hose, then there must be an obstruction in a line or fitting. I would connect an air hose from a compressor set at 30 psi to the city water connection like you would do if you were winterizing. This will allow you to test pressure in the lines without blowing water all over the place. Open the faucet long enough to get all the air out of the line. Find the cold water line that connects to the faucet and if it is a compression fitting you can disconnect it and then check the airflow there. If it is good, the obstruction is in the faucet body, maybe at the seats in the valve. If not, you will need to keep tracing back and disconnecting fittings until you find it.

However, if you have clamp-on fittings like the photo above, it’s not as easy. You can cut the clamp; however, you will need a clamp tool to reconnect with a new clamp. Use a heat gun on low to heat the pipe and fitting to pull the hose off. Once again, you will need to follow the pipe and look at every connection until you find it.


 You might also enjoy this from Dave 

What RV water pressure should I have at the campground?

Dear Dave,
When at a campground, what is the suggested psi setting for an adjustable water pressure regulator? —Tony, 2003 Holiday Rambler Vacationer

Read Dave’s answer.


Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here

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Fulltimer
2 months ago

If it’s a single lever faucet they have a diverter valve built in the faucet, that may be bad.

T G
2 months ago

Kinking PEX is pretty hard to do. It’s pretty stiff stuff. I suspect the problem is in the faucet. There should be a union type fitting where the PEX connects to the faucet. (A union type fitting is one you can rotate, to connect or disconnect, without rotating the piping).You can easily open these. Maybe pliers to get it started then by hand the rest of the way.

First, shut off the water, of course. Then disconnect the PEX at the faucet using the union type fittings. Then remove the faucet from the sink, take it to a work bench and dismantle the faucet looking for blockages. Reassemble everything in the reverse order. If you can’t get the faucet apart it might be time for a new one. Having the old one in hand will help you find one that matches the spacings.

Martysh
2 months ago
Reply to  T G

Maybe just switch the hot and cold lines at the faucet to see if the low flow moves to the hot side – That would eliminate the faucet as being the issue

Jim
2 months ago
Reply to  Martysh

This makes too much sense.

Snoopy
2 months ago

When we first got our Forest River 34QS I had a similar issue with low cold water pressure in the bathroom sink! I was amazed when I discovered a complete water manifold for every water usage in the motor home. You could adjust any faucet you wanted to. For some reason the bathroom cold water one was turned down a bit & all I had to do was open it to flow properly! That manifold is really cool if I was to winterize our motor home, but in So Cal it’s not so necessary!
Not sure if this will help Chris or not, but there may be a valve controlling those water lines!
Snoopy

J.R.
2 months ago

I have also seen a piece of stone (just a little bit bigger than a grain of sand) stuck at the cold tap itself, causing exactly the same issue.

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