Navien NPE 240 A2 Flame Loss

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KevinL

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Hi All,

I have a Navien NPE 240 A2 that was installed 3 months ago. I've noticed that in the mornings/first time I call for hot water the tankless will go through 4 short cycles before stabilizing and delivering hot water. The odd thing is the flow says 4.4-4.8 gpm which is inaccurate as I'm only opening a sink or shower at roughly 1-1.5 gpm.

Here is the events that happen when I call for hot water
- Start up
- Flow rate says 4.4-4.8 gpm for a second (sounds like a jet engine and the window flashes a bright blue flame)
- Post Purge
- Repeat

This must happen 4 times before hot water is delivered to the fixtures. If I stop it short (maybe 2 or 3 cycles) before the 4 cycles completes then the next time I call for hot water it must cycle through 4 times before hot water is delivered. The odd thing is throughout the day when I call for hot water after it's completed this 4 start up cycle it works flawlessly. I open a sink or shower and starts up and delivers hot water very quickly.

The advanced menu flame loss counter consistently increases (now in the 650 range after 3 months). 2nd, 3rd, 4th, etc ignition counts are 0 or minimal. I get ZERO error codes though and the hot water heater works fine after the 4 cycles. I'm more so worried about excess wear and tear and obviously the long delay the first time I call for hot water during the day.

Here are the things I've done to troubleshoot
- Cleaned air intake filter
- Switched electrical outlets
- Left the front cover off overnight and during start up to promote airflow
- Closed hot water outlet from the tankless and opened hot water taps to check for cross plumbing
- Close hot water outlet and attached a hose to hot water service valve to check for water pressure irregularities
- Factory reset
- Recirc is off (used internal recirc for a few days wondering if that may help, it did not)


Any advice, comments or suggestions are greatly appreciated. Thanks again!
 

Bannerman

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From your description, to me suggests insufficient flow to maintain constant WH operation.
The Navien specifications on page 26 indicate the minimum flow rate requirement is 0.5 GPM through the WH, not the flow rate at the faucet.

While you said your sink or shower operates at 1-1.5 GPM (seems low for a shower), depending on the water temperature from the WH, there maybe insufficient water continuing to flow through the WH once the temperature has risen to the WH set temperature. What is the hot water temperature setting?

When you first turn on the shower, it is likely almost all initial water flow will be flowing through the WH. Once the hot water arrives at the shower control, a pressure balancing thermostatic shower control will reduce the hot water flow rate to mix in additional cold water to acheive the desired temperature at the shower head.

As it seems your home is not equipped with a recirculation return line, recommend operating the unit with the optional ComfortFlow internal circulation mode enabled.

The NPE240-A2 manual states on page 27:
The recirculation feature of the “A2“ models has three performance advantages: ● Elimination of any minimum flow rate requirement. ● Elimination of any hot/cold/hot stacking—the “cold water sandwich“ effect. ● Quicker hot water delivery to fixtures, which results in less water wasted.

To enable the internal circulation feature requires not only setting the front panel control to Internal circulation, but also setting the internal 2-way valve to the 'Internal' position.
 

breplum

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Manometer is needed to confirm you have spec'd gas supply pressure. NG 3.5" -10.5" WC
Navien tech support number but you'll need a good plumber.
Do use internal recirc.
Years back, I had a few brand new units where ignitors were problematic and the free replacements solved the problem.
I would have thought whatever that glitch was would have been ironed out. Being mostly retired, I haven't seen an A2 model and don't have a troubleshooting manual. But "A" models would have to have a flame failure event over 20 times before an Error was set.
 

KevinL

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Thanks for the suggestions.

Bannerman - Hot temperature setting is 115 F. I am turning on the hot water only side of a two handle faucet (~1 gpm) in the morning to test.

Breplum - will double check the gas pressure.

Forgot to mention, during the short cycling I do smell a faint amount of natural gas, it quickly goes away once the unit stabilizes. Would it likely be because the natural gas is not burning completely due to the short cycling?
 

Plumber69

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Manometer is needed to confirm you have spec'd gas supply pressure. NG 3.5" -10.5" WC
Navien tech support number but you'll need a good plumber.
Do use internal recirc.
Years back, I had a few brand new units where ignitors were problematic and the free replacements solved the problem.
I would have thought whatever that glitch was would have been ironed out. Being mostly retired, I haven't seen an A2 model and don't have a troubleshooting manual. But "A" models would have to have a flame failure event over 20 times before an Error was set.
I had a new navien that was running at 4.2wc and had a simular issue. Bumped it down to 3.5 and it has been good ever since
 

KevinL

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plumber69 - that's weird. 4.2 is not anywhere near the upper limit for gas supply pressure on the Navien. Putting it at the minimum of 3.5 solved the issue for you?

Just to add I didn't use hot water all day until about 5 pm in the afternoon yesterday. Unit started up without the short cycling. Tested again this morning and it went through the short cycle again (4 times).
 

Plumber69

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plumber69 - that's weird. 4.2 is not anywhere near the upper limit for gas supply pressure on the Navien. Putting it at the minimum of 3.5 solved the issue for you?

Just to add I didn't use hot water all day until about 5 pm in the afternoon yesterday. Unit started up without the short cycling. Tested again this morning and it went through the short cycle again (4 times).
I mean I set manifold pressure at 3.5 at full born. Not incoming
 

John Gayewski

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I think I would get a combustion analyzer if I were you. Then when you get done with it I'll but it from you, because I've been meaning to buy one too. Preferably one that had been gently used at a used price. Lol
 

Fitter30

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What is the exact code being generated?

Screenshot_2021-10-17-12-46-53.png

Screenshot_2021-10-17-12-46-53.png
 

KevinL

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As a follow up to this post it seems that the 4 flame loss cycle on start up is happening more frequently as the weather turns colder. Any time the unit is idle for more than about2-3 hours now. After going through the 4 flame loss cycle (start up, burn, post purge, repeat 4 times) it starts up and works flawlessly. I've tested turning on hot water half an hour, 1 hour, 1.5 hrs, etc later after the 4 flame loss cycle and it works as expected. I'm wondering if the 4 flame loss cycle is related to a "cold start" for the unit? No error code is being generated, it is just taking longer for hot water to deliver as it must go through this flame loss cycle.

I will turn on internal recirc to see if it helps.
 
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