Lochinvar Noble Combi LP Venturi

kbaillargeon

Combination boiler installed in January 2018. Boiler activated around October 2018 after new propane tanks installed. Yes boiler was converted from NG to LP and complete combustion analysis was performed. Ran from October 2018 to around March 2019 before boiler intermittently would start locking out on "flame fail ignition". After about a week of intermittently locking out and unable to exactly pinpoint issue I finally disassembled boiler removing blower assembly, top heat exchanger plate and burner. Cleaned heat exchanger & burner. While boiler was disassembled I decided to remove ventuti from blower assembly. This is when I noticed venturi was stuck and occassionally sticking. I reassembled boiler and boiler components. Eventually boiler locked out the next day. I disconnected rubber furnco from venturi to find venturi was stuck. I stuck a popsicle stick inside venturi and freed it up. Reset boiler and it ran fine until 2 days later. I decided then to replace venturi completely. It then ran fine from April 2019 to November of 2019 where problem started up again. Same symptoms. I ordered a new venturi, reached out to local manufacturers rep and proceeded to disassemble boiler again. Cleaned heat exchanger, cleaned burner, reinstalled blower assembly and installed new venturi. Completed combustion analysis and submitted to manufacturers rep. All good and no clear explanation to why this is occurring. Come March 2020 same problem again. I'll note that heat exchanger and burner were not dirty or anything unusual. In addition the exhaust goes out the back of the house and fresh air intake is piped to the front of the house. Please advise on any thoughts.

DZoro

What is your gas pressure, static, 100%, and low fire?
What size and type of gas pipe?
How far to the regulator?

kbaillargeon

Gas pressure- 13.5” w.c. static, hi fire & low fire.
Material- Schedule 40 metallic pipe. Approximately 30 feet of 1” from propane tanks to tee & 5 feet from 3/4” tee to boiler. The propane regulator is located at the tanks. The result of the “flame fail ignition” failures are all related to the stuck venturi. I’ve never had an issue with an ignition failure related to gas pressure or gas regulator.

DZoro

Just checking the gas. I have not seen a issue with the venturi sticking either lp or nat. I have had a issue when the lp venturi was not seated and sealed to the blower frame tho. Ask me how I know this . When not fully seated small amount of extra air comes in and messes up the ignition. Maybe double check the static plate gaskets (2) and the venturi gasket and screws.
That back screw on the ventor is a bear, and certainly can cause some issues.
One other note, the only boiler that really caused some issues for me was one that was plumbed outside similar to yours. I know the factory says it's good to do that, but....
Just maybe different wind currents are playing with air pressures inside the boiler
D

kbaillargeon

Originally I was using room combustion air from an unfinished basement where boiler is installed. The manufacturers rep was adamant about piping fresh air intake to the outside because they suspected contaminated combustion air from basement may be the cause. As you can see that didn’t fix it. My suspicion is something within the propane, that’s almost deteriorating the plastic of the venturi. As I previously said when the unit runs, it works great, no ignition failures until the venturi starts sticking. There have been some windy days and nights here in New England and I’ve never had an ignition failure because of wind currents.

DZoro

You're actually having deterioration with the ventruri, then yes it's taking in something besides good air. Look around you for any detergents, pool chemicals, other exhausts. There's a product in that area that it doesn't like.
D

kbaillargeon

The boiler ran 6 months with fresh air intake piped to the outside. There’s no dryer exhaust or exhaust terminated in the front of the house where intake is piped to.

hot_rod

Is this the manual Venturi damper you are talking about? What is causing it to stick? Crud in the flapper or is the composite distorting causing it to bind?

kbaillargeon

It's the venturi thats mounts to the blower assembly. Not exactly sure what is causing venturi to stick. I suspect it's related to propane. There's isn't debris or composite causing it not to open. What happens is the plastic flap sticks to the bottom of the venturi. Once freed up, the flap moves freely for some time before sticking consistently and eventually needs to be replaced.

DZoro

Propane or its gasses should never come in contact with the flapper. Is it in a dusty location, ex dirt roads, driveway...
D

kcopp

I had that happen 1 time on a Greenstar Combi. The boiler was vented through the roof. Both intake and exhaust.
They (Bosch Tech) recommended powdering the flapper so it wouldn't stick. I think its just a bad material design material that gets gummed up.

ryoung02

I have been having the same issue for a couple years. I used a powder lubricant for a while but the problem still returned after a while. Contemplating the use of a Teflon coating to prevent the sticking. Are there any LP gas filtering or drying treatments that might help?

GGross

ryoung02 said:

I have been having the same issue for a couple years. I used a powder lubricant for a while but the problem still returned after a while. Contemplating the use of a Teflon coating to prevent the sticking. Are there any LP gas filtering or drying treatments that might help?

Your venturi flapper should never be coming into contact with any form of LP gas. More than likely your problem, as well as OPs has to do with flue gas recirculation. Your flue exhaust pipe is probably near your intake and the intake is probably sucking those fumes back in. The sticking is a symptom of a problem, but not the cause itself, you can hide it but it will just cause larger issues down the line. For additional assistance I recommend making a new thread to keep these separate