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We purchased a house with an existing tankless heater (installed in 2009). It would occasionally fail with error code 11 (no ignition). Over the past 2 months it has been failing more often and now fails every day.

The odd part is that it never fails first thing in the morning (6:00am) and almost always fails in the later afternoon/evening. We've tested this theory continuously over the past few weeks.

I've taken two videos: One in the morning where it works: https://youtu.be/l0XuhanKNCw

And one in the evening when it does not: https://youtu.be/drKBS0QDyhk

The unit was originally installed with a 1/2" gas line. I've recently had it replaced with a 3/4" line, as per the installation instructions, to see if that made a difference (it did not). It's unlikely it's a venting or air intake issue.

Why would time of day have any impact on the the unit working? Does anything seem off here?

Thanks

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    The only thing I can think of would be with cooler temps in the am there may be more draft providing a better chance of ignition. Is there a fan on the exhaust? I could not if there was water running or a fan. Checking the air vents to the burner to make sure spiders or dust is not preventing a proper air gas mixture may help it start better. – Ed Beal Sep 24 '16 at 15:12
  • Can you post make and model. – spicetraders Sep 24 '16 at 15:44
  • There is a blower motor inside the unit that brings in air from the front of the unit (uses inside air) and exhausts through the top of the unit. The intake filter is clean, however I have noticed that the blower motor doesn't sound great sometimes on startup. I guess I can try forcing some air through the intake (hair dryer or fan) when it's failing to see if the extra air flow helps? – Richard O Sep 24 '16 at 15:51
  • Rheem Model PTG2-42PVN – Richard O Sep 24 '16 at 15:52
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    This may be the case of cold solder joints on the controller mainboard. In the past I fixed appliances by re-soldering all joints on the mainboard with good quality lead based solder. – ajeh Aug 10 '17 at 14:43
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Shot in the dark here, but is it possible it only works when you don't have other gas appliances running (furnace, dryer, stove etc.)? Some of the tankless units draw massive BTU's (199,000+) and you might not have enough of a supply to your house to run the tankless and another gas appliance. I wanted to recently upgrade to a tankless but didn't because it would have required replacing my gas meter and about 50ft of blackpipe just to get enough gas capacity for everything running at once.

Also, your intake should really be using outside air. Is the unit installed in a confined space? Or is the space it's installed very tightly insulated/sealed from outside air penetration?

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