Navien combi will not heat house above 68, ran constantly from November to April

hudsoncorp

Navien combi NCB 210, Serial # 7965201408041060, Engraved plate inside unit: 56321Built 2014Serial #
15055201407252067
Would not heat the house above 68 degrees all last winter, 62 in cold snaps
Contractor has walked away
Cold weather coming, need to know what's wrong & get it replaced with a cast iron boiler
Point Pleasant NJ
Exit 98 off Garden State Parkway

Paul48

You don't need to replace that boiler. You need a good contractor to tear all that near-boiler piping out and re-do it. Form what I can make out.......They got the "pumping away" part right, but have the supply and return pumping away.

hudsoncorp

Thanks for the comments!
1940's, 1400 sq ft., brick, well insulated crawl, some insulation in attic
How do I reach Snowmelt?

njtommy

Wow. That's a rough looking install

hudsoncorp

Contractor claims it is state of the art!

njtommy

Well the Combi is, but I'm sure it's installed wrong and pipeing/ zoneing is wrong.
I have a Navien NCB boiler in my own house.

hudsoncorp

What do you see that is wrong? System is one continuous zone. Suggestions?

njtommy

I'm assuming baseboard?
How many floors?

Harvey Ramer

Condensate neutralizer is not doing a lot of good in a vertical position. Needs to be horizontal with inlet bottom and outlet top. Or vertical with a trap on the outlet to force the neutralizer to stay mostly full.

What kind of emitters do you have? Those Navien combis only produce nameplate BTUS on a low temp emitter system. They are limited to about 5 gpm through the boiler.

hudsoncorp

1 floor, old cast iron covered with steel baseboards, some Slantfin sections added

hudsoncorp

Harry: How to find out what emitters they used?

Paul48

Take some pictures a little farther back, so they include more, if you can. The air scoop is useless as it is piped. There are piping restrictions that are clearly addressed in the instructions, for it. What is the pipe coming out of the supply side, above the closely spaced tees?

njtommy

do you know what the supply water temp is?

hudsoncorp

Probably the water filter--blue pex--originally they had it filtering the baseboard water! Now bypassed.

hudsoncorp

Tommy: Yes-single story home

Paul48

No....the black pipe that comes out of the navien, then tees off.

Harvey Ramer

Get yourself some strap on thermometers or a laser thermometer gun. Turn you thermostat up as high as it will go. Let the boiler run for 20-30 minutes. Then measure the boiler supply and return on the boiler loop. Also measure the supply and return on the system piping.

Report back.

hudsoncorp

Paul: If you're talking about the black pipe almost dead center, tees off to the left to a ball valve, it's the gas line

njtommy

. Min firing rate on that boiler is 18,000 btus I'm thinking it's short cycling like crazy, but that's me assuming

Also boiler will tell you on the display screen the supply water temp.

hudsoncorp

Harvey: I'll try to get temps tomorrow

Paul48

No.....Behind the ball valve for the gas. The pipe tees to the left and goes up.

Rich_49

Hudson ,

Contact me ! I'll be in Point Wednesday and would like to take a closer look .

hudsoncorp

Additional photos just taken

hudsoncorp

Paul: Low water cut off to top left of unit

Harvey Ramer

You may be on to something there, Paul. I'm wondering if that might be the system return. You can't really see any pipe continuing on the right of those closely spaced tees.

Paul48

Wow........Let Rich straighten that mess out. You won't regret it. If your installer had opened the I&O manual, he would have known that there is a low water cut-off inside the boiler.

hudsoncorp

Thank you all for your comments! I will check again later for any updates.

Harvey Ramer

Hatterasguy said:

The problem with the system is the fact that it is most likely overpumped and the DT is smaller than 20. This results in the boiler modulating itself down.

A proper DT circulator will fix your issue.

Care to elaborate Hat? I fail to see the system react as you described.

Ironman

Hatterasguy said:

Harvey Ramer said:

Hatterasguy said:

The problem with the system is the fact that it is most likely overpumped and the DT is smaller than 20. This results in the boiler modulating itself down.

A proper DT circulator will fix your issue.

Care to elaborate Hat? I fail to see the system react as you described.

Sure.

If that big B&G results in a system DT of 10, the Navien will immediately modulate downward to compensate. Remember, it has a constant flow rate of 5 gpm on the onboard pump, so, with a DT of 10, it only needs to put out 25K to meet the specified SWT. But, 25K won't heat the house.

Slow the pump down, get a DT of 20, and the output of the Navien doubles to 50K.

The dangers of being overpumped on a mod-con...........rearing its ugly head again.

Most of them won't put out anywhere near their specifications without a huge system DT (which may not be obtainable).

We had a similar discussion on the Viessmann last winter with a fellow who was cold all the time. It had to have a system DT of 35 if you wanted its full output. He didn't have it.

This NCB-210 offers a DOE of 95K. But, the only way you ever get it is with a DT of 38. Good luck with that.

That sounds plausible at first, but if the boiler doubled its firing rate because you widened the delta T, then wouldn't the the delta T be the same as before and the boiler would then reduce its firing rate again?

Paul48

Been down this road before........Widening the DT with the pump, leaves more btus at the boiler. And now the buffer tank guys usually chime in. It's deja vu all over again!

Harvey Ramer

Mr. Hudson,
Did you take the temp measurements?

hudsoncorp

Harvey: Rich & John were here today but, I do not recall what the temps were. I think it had a delta of 20.

Paul48

Well...........What was the verdict? I think I speak for everyone, when I say I'm dying to know.

Harvey Ramer

Yeah, fill us in.

njtommy

Pretty much Paul.

hudsoncorp

I too am waiting for their conclusions. Given the existing conditions, a mod con should never have been considered. High temp water & cast iron boiler appears to be the answer. Now I have to get it replaced or a refund of $10,200.00. I expect Rich or John will post when they are ready.
Thanks to all!

4Johnpipe

Rich will fill you guys in more on this. Several obvious issues... System is a mono-flow with globe style "T's". Major air issue as the scoop cannot remove in current position and lacking a good manual purge set up. Had sporadic temps and the boiler return was reading higher than supply. Did read 20* DT at start up. Not happy with a single size secondary loop seems to be sending too much return back to boiler. Hydrolic separator would have been preferred or at least up-size the secondary loop. With a max temp of 194 and the existing construction would have recommended low temp baseboard. I would guess the original boiler was set to 210* or so...

hot_rod

I would certainly upgrade to a higher efficiency air purger. Even installed properly, those scoop type do not remove micro bubbles. A boiler like that and a mono-flo system really cry out for 90% plus air removal.

What model is that circ? It may not be oversized?

george_42

The only reason your present boiler is not heating your home is that it is not supplying the emitters with water at the required temp(usually about 180). Your old boiler was putting out those type of temps and your radiation was designed for those temps.You have to find a way to increase the supply temp or add more radiation.Most mod con boilers are designed to put out about 130 degree water and that will not do it.

HDE

Could it be a simple as the wrong reset curve selected or programmed? Or the high temperature operation capability was not activated with the correct venting used?

Rich_49

There are several reasons why this boiler is not heating this house . Not just one . This boiler is not utilizing outdoor reset so that is not an issue . Boiler was not connected to odr last winter either . This is a much more complex multitude of problems that touches every part of this system and most importantly whom the guys are proclaiming to know what they are doing that don't . These contractors were given a green light to do the Cadillac job yet did not perform their due dilligence to recommend and install the right combination of stuff .

I will post everything that is pertinent by this evening .