From the Girard owners manual:
E6: Over Temperature.
Outlet Water Temperature has exceeded 140°F (60°C) for 3 sec.
We had this problem once with our Girard Gen 3 unit when we were in Florida.
EDIT: It may be a bad chip that controls the upper temp shutoff. Below is what caused our issues with an E6 and maybe something in this will help troubleshoot. It also may be a bad cooling fan. Have you verified whether it is running once the unit shuts off? It should continue to run for a period of time to cool things down internally. End of edit.
Discussed it with Girard Support and they surmised that it was due to the incoming water temperature being too warm to begin with and we weren't able to create enough flow thru the unit to keep it from overheating.
One of the Girard's tankless water heater's downfalls is it's single stage burner. It's either on full blast or it's not. And depending on the flow rate thru the water heater and if the source water is too warm to begin with, the water passing thru the unit may stay longer than desired and end up being heated over the 140 degree upper limit. When that occurs, the unit will shut down.
The solution is not always easy depending on your situation. You need to try and increase the flow rate thru the unit if possible and can sometimes be done by trying one or a combination of these suggestions.
1. Making sure your not mixing in cold with the warm to allow as much flow thru the water heater as possible.
2. Removing any flow restrictors that may be installed in your fixtures.
3. Turn on the hot water in more than one location to maximize flow thru the unit. Example is turning on the bathroom hot water in the sink when showering.
4. If your in a low pressure situation, try filling your fresh water tank and use your water pump instead of simply relying on the pressure alone at the campsite.
In our instance, none of that worked and after discussing it with Girard, they determined that a chip in our unit needed a higher rated one. They set the limit at 140 more to prevent accidental scalding than that the unit can't handle higher temperatures so their solution was to have a higher limit chip installed in our unit.
First, they sent me a replacement chip to try and replace it myself in our unit and although an easy task technically (screwdriver), due to it's location in the back right corner of the unit, you would have to almost disassemble the unit to get to it and it wasn't something I wanted to try while 1500 miles from home.
So believe it or not, they actually shipped me a replacement unit to our park with the higher temp chip already installed in it, paid to have a mobile installer swap out the units and then paid for me to ship the old one back to them. THAT resolved our issues. I can't praise them enough for their support and efforts to make things right.
Sadly though, a month or so later, the cooling fan in ours failed and the replacement for that one did so a few months after that for another completely separate issue.
So we just gave up and replaced it altogether with a Truma AquaGo Comfort model and although pricey, it just works. Multi stage burner, can heat water at a trickle or full blast, mix cold in as much as we want, no more setting temps, can turn the hot on/off/on/off/on and due to the mixing tank, no cold water sandwich, etc. We use our hot water just like we do at home.
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