I have an Eccotemp L10 Tankless Water Heater. This unit was installed two years ago and it has been used since for all our hot water. It worked great for 6 months and then we had to replace the gas-water valve assembly. About 6 months later I had an issue with it periodically/randomly not igniting (no spark) and that I was able to fix by trimming the wire that leads to the flame sensor. Other than these two issues the unit has performed well until October of this year. Then an unusual issue occurred for which Eccotemp tech support has no answer.

In October, the water heater started having ignition failures on a periodic basic. When the water was turned on it would flare for a second and then go out. Sometimes it would not even flare up at all. This problem only occurred first thing in the morning and after 30-40 minutes the unit would work normally. Removal of the cover showed that the unit was getting sparks, just not igniting or sometimes igniting and not staying lit. I reset the gas-water valve assembly back to factory settings per tech support instructions, to no avail. We installed a new hose and regulator but after a couple of days the problem reoccurred. We then installed another new gas-water valve assembly, but after about 10 days the problem reoccurred.

Through careful observation we have determined that the failure to ignite (or stay lit) occurs when the ambient temperature gets below 55 degrees F. The water heater is mounted in an outdoor kitchen that is semi-enclosed so the temperature in most of the area rarely gets below 40, even when it's in the 20's outside. This happens even though this unit is made to be installed outdoors with strong admonitions to drain it during freezing temperatures. And I am also sure that there is no ice in the water flowing into the unit.

After experimenting with different water temperature and flow rate settings, we discovered that at 55 degrees or less, the water heater will ignite only if the heater's temperature setting is turned to its coolest level. Then the temperature can be turned up, with the water still running, and it will continue burning. If the room is really cold (40's to low 50's), the heater won't even light on the lowest setting. At that point, we light our tanktop propane heater and place it so that it is almost underneath the water heater, until the unit warms up and then the unit will operate again. Since this problem started, I've also noticed that when it's cold and the unit does light with the temperature set on medium or higher settings, there is somewhat of a "pop" sound when it first ignites, as if gas is accumulating before ignition occurs. We have had NO issues lighting a tank top heater or burners on our cook top that are in the same room. All of these appliances use 20lb propane tanks that we have filled at the same place. The water heater problem has occurred with multiple different tanks of the past two months.

Eccotemp tech support has no answers other than to send the unit to them. They say there are no issues with this heater that can be temperature related. However our experience with this water heater has shown the issue to be consistently related to the temperature. Looking back on the troubleshooting in October, we can see that the days where we had no problems were days that followed warmer fall nights.

I have since bought another L10 water heater but I would like to have this one repaired to keep as a spare. I also want to know what went wrong. I've considered sending it to Eccotemp for repair, but the manager of the tech department seemed to not have a clue what the problem could be which makes me leery of sending it to them since I will have to pay by the hour for them to troubleshoot the issue. I really don't think they'll even be able to replicate the problem if they have the unit in a shop that is warmer than 55 degrees.

Does anyone here have a suggestion as to what the problem could possibly be or what I could try to fix it?

Thank you.

Here is a link that might be useful: Eccotemp L10 Water Heater