Navien NPE-240A2 - temperature fluctuations

GinoDivx

I just had Navien installed (NPE-240A2). My issue is that shower in main bathroom seems to have colder water than when I had regular water heater. But more importantly, when someone turns on a faucet or another shower nearby, the water becomes even colder. Not totally cold, still warm, but not hot. I have a separate return line, seems to be connected properly, the line is hot, and hot water is available almost immediately everywhere. I called Navien, and they suggested to flush the heater (which was just installed last week), with contractor present, and call them, to possibly diagnose check valve. GPM was ~4.2GPM when I checked. Can check valve or something else be a problem with brand new heater? Thanks!

Jamie Hall

4.2 gpm? What's the incoming water temperature -- any idea? And what do you have it set for for output temperature? That unit should be capable of a 90 F temperature boost at that flow rate, but that's all it can do.

Larry Weingarten

Hi, I would check to see if you're getting back flow through the check valve on the recirculating system. Also are there any mixing or tempering valves installed? Sometimes they can leak cold water into the hot side. And, your shower may have a built in limit that needs to be adjusted to get hotter water. Finally, you might do a crossover test to make sure cold isn't leaking into the hot side from someplace. To do this, shut off water to your new heater and open a hot tap. Water should stop flowing in a second or two.
Once you know it is not the plumbing causing the problem, it's easier to focus on the heater itself, if needed.

Yours, Larry

ps. Do you have multiple showerheads? Maximum hot flow should be about 70% of 2.5 gpm or 1-3/4 gpm for your shower... not 4.2.

GinoDivx

@Jamie Hall - Incoming is prob outside temp, so maybe 40-50? Output is 120F.
@Larry Weingarten - I will try. But here is the thing - I lived in the house for 15 years when we built it, and I had 50 Gallon high efficiency tank before, no such issues. Recirculating was don via always on pump for the first few years, then I turned it off. Never had similar issues...

Jamie Hall

If you are really flowing 4.2 gpm, you are pushing what that unit can do in terms of temperature rise. Check that the installer made sure that it is really producing the maximum power it can, and that there is no "ghost" flow to something else.

pete_martini

I had a similar issue.
Two things to check,
One is the cartridge in the main bathroom. Over time sometimes the balancing spool in the valve can stick and not regulate hot water delivery.
Second is the temperature limit stop on the valve. If your tank heater was set at max 150F and your new tankless is set at 120F that 30F delta can be your cooler temp at the shower.

David Penz

I think Pete_Martini is on the right track. The single-handle shower faucet mixes hot and cold, the maximum temperature limited by a cam inside the faucet. With lower setpoint temperature (120F compared to, say, 130F or 140F), you will need to change the cam setting in all your single-handle shower/tub faucets. Alternately, you could adjust the tankless setpoint up, but efficiency will be reduced.

I wish you well with your new tankless heater. It may not be as reliable as your tank. Also, whereas continuous pumped circulation is OK with a tank, it is not usually OK with tankless. Read your instruction manual and your warranty carefully. The pump may need to be controlled by the heater itself, or from a short period repeat cycle timer.