Hot water out of all cold faucets 2015 Itasca Sunstar

[Cconk]

Scalding Hot water out of all cold water faucets! Installed new thermostat, circuit board & checked for open valves. Can’t fix 2015 Itasca Sunstar

 

[Morich]

This sounds like it may be a check valve that has failed but we will need to know which Sunstar to pull up the correct drawings to verify that idea?
The whole group of interactive parts drawings are here but it often takes a bit of getting used to them to get the quicker answer.

Parts Catalog

Welcome to the group and hope we can be some help.

 

[Morich]

Doing a random check of a number of this RV, it loos like several have the same basic setup at the tank. Maybe you can get the general idea to check for these parts? Your RV may not look exactly the same but look for check valves. These are often called one way valves as they allow flow in only one direction---when working right!

I did some markups of flow. The blue lets cold water in as faucets are opened. The red line and check there let water out. When all faucets are closed they should both go shut! I also marked the bypass route for when you are storing and add antifreeze!

But I think the problem is the lower check valve has stuck open! This being open and the water heater heating the water in the tank, lets hot water back out into the cold lines and it can then flow to the faucets!
The top one on the hot line is to help keep hot water in the tank, rather than creeping out into the lines and cooling while you are not actually using hot water. but it does open when the faucets are opened to let hot flow.

I suspect the lower is stuck open but do check the part number for your specific RV as I did not check verify that correct for your model!!

 

[jdkbrooks]

I don't understand how the cold water lines can have anything to do with the hot water lines even if somehow the hot water was being pushed back through the cold water inlet it still wouldn't come through the faucets I've had hot water come through the cold water side went my hose was laying out in the sun.
Following

 

[cdeldorado]

I posted this fix to my 2023 Winnie a few months ago. Perhaps this might explain it...

2023 Winnie Vista 29NPF galley faucet cold runs hot for first 15 seconds

With the water heater warmed up and turning on the galley faucet on just cold, it would always run scalding hot for the first 5 to 10 seconds. After staring at the plumbing feeding the hot water heater and the faucet, I surmised that what was happening was that when the cold water is turned on...

www.winnieowners.com

 

[Sojourn]

Scalding Hot water out of all cold water faucets! Installed new thermostat, circuit board & checked for open valves. Can’t fix 2015 Itasca Sunstar

We had a strange situation where a friend hooked up his water to the drain of a hot water heater that was on the side of a building! It looked like a faucet!