Replaced RV’s on-demand water heater; why no hot water in sink?

Dear Dave,
I just installed a brand-new Girard tankless water heater in my RV. The original Girard produced way too much hot water. The dealer said it could be a number of things, so I just put in a new heater. All is good except I can only get cold water in the bathroom sink. Shower and kitchen sink are fine, having both hot and cold water, but not the bathroom sink. It’s so frustrating. Any ideas? —Jeff, 2017 Jayco Greyhawk 31FS Class C motorhome

Dear Jeff,
The Girard (owned by Lippert) is a typical compartment-mounted water heater with a traditional cold in and hot out line.

This back photo shows the cold inlet at the bottom left with a min/max adjustment, and the hot outlet just above it. The inlet to the lower right is the LP line.

Possible causes

If you had hot water to all the faucets prior to installing the new system, you must have pinched a line or somehow removed a “T” or other connection. Since there is only one hot outlet coming off the back of this, the hot water is forced out of the system and goes through the PEX tubing to the faucets and shower head using “T” connections to tap into the main line and supply hot water.

Since the water heater is “downstream” of the fresh water tank and water pump, I doubt it has anything to do with being on city water or using the water pump. And when removing the old water heater you should have just removed the hot and cold water pipes at the connections and the LP line without doing anything to other water connections.

However, you most likely drained the water in the system and that would mean opening a low point drain valve. Check to make sure all the valves are closed, as this might be where the hot water to the bathroom is going. It does seem odd that the shower has hot and not the sink. However, as I’ve stated many times, I never say never when it comes to what RV manufacturers do.

How to test for location of issue

If all the drains are shut, then I would make sure the unit is not connected to pressurized city water and the water pump is off. Relieve the water pressure by opening one of the hot faucets that work. Then remove the hot water line to the faucet that is not getting hot water and insert it into a 5 gallon pail or small plastic bin if there is limited space. Turn on the water pump to see if anything comes out. If water comes out of the pipe, you have found the issue—it is in the faucet. If not, you will need to trace that water line back through each of the connections.

Before cutting the crimp rings at the connections, I would try using an air compressor set to 40 psi connected to the hot water line coming off the water heater. You will need an air blow gun like this one from Amazon.

Insert the tip into the water pipe and force air into the line and see if the disconnected hose has air flowing through it. If it does, it’s the faucet once again. If not, it is back to tracing the line all the way back to the water heater.

 You might also enjoy this from Dave 

Can I install a single on-demand water heater for RV’s kitchen and bathroom?

Dear Dave, 
I purchased this trailer in November 2021 from Lazydays outside of Memphis. It was known I was taking the trailer to my home in Maine. The trailer was parked all winter in Maine. In the spring I took it to my lot in Northern Maine. Well, all the water lines were damaged, and the water heater didn’t work. Lazydays apparently hadn’t winterized the trailer, and I never asked them if they did. My question is, can I install a single on-demand water heater that would take care of the kitchen and bathroom? Usually, it is just me at the trailer, so I don’t use a lot of hot water. Your sage advice will be appreciated. if my solution isn’t feasible, any advice? —Bill, 2018 38-ft. Keystone Cougar fifth wheel MKS37

Read Dave’s answer.

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

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