Navien NCB-240E Combi-boiler ignite issue

[gt5oh]

I have a Navien NCB 240E combi-boiler set up for hydro space heating and domestic hot water (installed 2019) I am having an ongoing issue and can't figure it out. My domestic hot water side is set to around 125 F. When I turn on a faucet to call for hot water, the flow rate is 0.6 GPM. The boiler will heat up to 125-130 F temp and hold for a few minutes. Then the temp starts dropping, and I hear the boiler trying to re-ignite as if it's trying to heat up again but it goes into a cycle and is unable to heat. Eventually the temp drops because the unit cannot fire up again and the water starts cooling and then its very cold water at the faucet. The boiler will continue this cycling when calling for hot water and eventually after a few minutes sometimes it will work and start to heat and sometimes it will stay in this loop. The machine shows no error codes.

Video of the issue, listen to the audio - Navien NCB 240E Ignite Issue

I reached out to Navien and they said to contact a local plumber who is an authorized tech, which I have done, just waiting on them to firm up an appointment. Wondering if anyone else has encountered this.

 

[gt5oh]

Plumbers seem to think its a flow issue. Faucet is hitting 0.6 GPM. Navien unit minimum flow is between 0.5-0.6 GPM. If the flow is too low the boiler won't kick on to heat.

 

[Tim Whistler]

Are they able to increase flow at all? I had an issue starting up a new Navien Combi boiler about 2 years ago where it would not fire and luckily a good friend of mine with a little more experience told me that with the Naviens I needed to set the pressure up over 15 psi on the boiler feed and that works just fine.

 

[RS]

Plumbers seem to think its a flow issue. Faucet is hitting 0.6 GPM. Navien unit minimum flow is between 0.5-0.6 GPM. If the flow is too low the boiler won't kick on to heat.

That would be easy to troubleshoot, just turn on 2 or more faucets! Could be something as simple as a clogged aerator!

 

[Twowaxhack]

Seems to me if the unit is trying to fire then there is enough flow. It won’t try to fire unless there’s minimum flow.
Maybe it’s borderline and it bounces between not enough flow snd just enough.

I had a defective Navien that wouldn’t fire reliably. Ended up being a design flaw defect.

I hate Navien as a company

 

[gt5oh]

Plumber said that the faucet fixtures are calling for flow at 0.5 GPM to 0.6 GPM and the minimum flow requirement on the Navien is 0.6 GPM for it to kick on. I checked the aerators and the internal plumbing is all new pex so I doubt lines are clogged.

Why would Navien make the minimum flow 0.6 GPM. The plumber advised I would probably need a fixture with a high flow aerator or remove the aerators. So basically I have to use more water than I need in order for my boiler to produce hot water...seems counter productive and not that efficient.

I removed the aerator from one of the faucets which brought the flow up to 1.0 GPM, the water splashes everywhere but it seems to remain hot with the higher flow. The fixtures are only 2 years old so I would hate to have to go and replace them all. Can I buy third party high flow aerators instead?

 

[Twowaxhack]

Sure, you can buy aerators that deliver different flow rates.

 

[breplum]

The min. flow on your unit is .5 GPM ( see Ncb E Brochures Ncb E Quickfacts En | Downloads | Navien)
You certainly can buy aerators in any flow rate you desire. It can be tricky to get the threads right. For that, a good plumbing supply house or hardware store usually has a thread match plate to correlate. You can also often disassemble some aerators and drill out the restrictions just a tiny bit for desired effect.
I know many plumbers who drill out the flow restrictor internals from shower heads, kitchen faucet check valves and check valve flapper of recirculating hot water systems ad nauseum.

 

[gt5oh]

Thank you, what would be the benefit of increasing PSI pressure on the Navien boiler?

What should be the optimal operating pressure?

 

[Tim Whistler]

In my case the Combi would not fire after we installed it at the standard 12psi boiler pressure. When we cranked it up to 15-16 psi it was fine.
Doesn't sound like that's the problem with yours from further threads.
I have to say tho- .5psi is a trickle, basically what I shave with in the morning, and my Navien NPE 240 water heater only is fine.
Are all your aerators REALLY less than .5psi? That's barely anything! It sounds to me like there is more going on with the unit..

 

[Twowaxhack]

In my case the Combi would not fire after we installed it at the standard 12psi boiler pressure. When we cranked it up to 15-16 psi it was fine.
Doesn't sound like that's the problem with yours from further threads.
I have to say tho- .5psi is a trickle, basically what I shave with in the morning, and my Navien NPE 240 water heater only is fine.
Are all your aerators REALLY less than .5psi? That's barely anything! It sounds to me like there is more going on with the unit..

.5 gpm not psi

 

[gt5oh]

In my case the Combi would not fire after we installed it at the standard 12psi boiler pressure. When we cranked it up to 15-16 psi it was fine.
Doesn't sound like that's the problem with yours from further threads.
I have to say tho- .5psi is a trickle, basically what I shave with in the morning, and my Navien NPE 240 water heater only is fine.
Are all your aerators REALLY less than .5psi? That's barely anything! It sounds to me like there is more going on with the unit..

I believe your NPE has a lower minimum flow rate which means it heats water even if the flow is low. My NCB 240E must have .5 GPM in order for it to kick on. I wish I knew this before I bought it otherwise I would have found another system with a lower minimum, especially now when all fixtures are trying to conserve water. Many faucets come with regulators and low flow aerators to conserve water. I've had issues with a waterfall style faucet that was only getting .5 GPM and would not even trigger my boiler, therefore no hot water. I had to open it up and put a small hole through the internal regulator to bring it up to .8 - .9 GPM in order for my boiler to even heat the water. Its ridiculous that Navien even has a .5 GPM requirement for their expensive machinery to work properly.