Lochinvar Goes Through Two Ignitions

OaklandNS

I have a Lochinvar Knight wall-mounted boiler (WHB-55). I've noticed when it gets a call for heat from a cold start, it will go through two ignition cycles back to back (Pre-Purge, Ignition for short time, Post-Purge, Pre-purge, ignition, runs just fine until heat call is over). The ignition counter registers both cycles. I suspect this isn't normal and was wondering if anyone on the forum could confirm and/or offer a suggestion as to what might be the issue.

I did do a combustion analysis per the manufacturer's instructions using a digital combustion analyzer and all is running within the manufacturer's guidelines.

Alan (California Radiant) Forbes

Check your incoming gas pressure with a manometer and record the pressure drop when it tries to ignite. It should not be more than 1-1½ inches wc.
If that's OK, check the condition of the ignitor. They do a lot of work and often, the electrodes get out of whack and they are too far apart for proper sparking.

OaklandNS

Gas pressure sounds like the culprit. There is some mild foghorning/rattling when it starts up from time to time. The gas line is 1/2" galvanized (short run from a 1.25" galvanized supply) connected with a piece of 1/2" CSST going to the boiler. I read elsewhere that increasing the CSST to 3/4" I.D. can help with this sort of thing. Sounds like it's worth trying. I'll have to borrow a manometer from PGE to test the WC drop.

Thanks!

DZoro

Agree with the gas pressure. Gas piping sounds questionable. Fog horning watch your analyzer and flame signal. Keeping both CO low, and flame signal strong 9+ you can then tune out the fog horn at the % fire that is causing the issue.
None of this can be done until your gas is spot on.
Is this a new or old install?
D

OaklandNS

It's a new install. The plumber put in a 1.25" steel supply line that runs about 60 feet from the meter to within about 10 feet of an on demand water heater (199K btus) and the boiler (55K btus). The boiler is fed off the 1/2" steel line that switches to an appliance hose right below the boiler.

DZoro

Nat or LP?

OaklandNS

natural gas

DZoro

Your gas piping is really close to being short. Close enough that you will need exact measurements of 1 1/4, and any other sizes and lengths of each.

OaklandNS

Hmmm, based on what the plumber and I talked about it seemed like 1.25" was sufficient. According to the utility/California code chart it can carry 528,000 btus with .5" WC drop which is about double both appliances' inputs. I'm not expert and did rely on him for this ... but it made sense to me at the time.

JUGHNE

The 60' factors into the equation, it is a major issue.
Pipe is reduced 10' before WH?
Need to check pressure when the WH first fires.

OaklandNS

Sorry, the table says a 60' run of 1.25" pipe can carry 528,000 btus with a .5" WC drop, so I was considering the 60' run. I'm not sure how close the 1.25" gets to the water heater because I didn't measure it, but it's less than 10'. I think that the 1/2' to the boiler feeds directly off the 1.25" before the reduction for the water heater.

OaklandNS

I measured everything more exactly and calculated pressure drop based on the ICC fuel gas tables A.3.4 and A.2.2 (https://codes.iccsafe.org/content/NYFGC2015UP/appendix-a-ifgs-sizing-and-capacities-of-gas-piping). The first calculation is very conservative and shows .7" WC drop to the boiler using BTU values higher than actually served by the branch (199K water heater and 55k boiler). The second uses the values that are quite close to my loads, but slightly lower and shows .49" W.C. drop. I haven't gotten a manometer yet but it seems to me like the piping ought to be sufficient--did I do this more or less correctly? I am attaching a pic of my calculation.

Alan (California Radiant) Forbes

Want me to come over and check your pressure?

OaklandNS

Wouldn't hurt. I'm a little worried it will be too low .... I'll give you a call.

delta T

How old is the meter/regulator setup from your utility? I just ran into one doing the same thing, piping was fine, but monometer showed a slow creep when static up to about 15" then drop to 6.5 when at high fire. Seems like it should still work fine, but foghorned like crazy. Utility changed the (65 year old) meter and reg and now 7" static, 6.5" when at high fire, and everything works fine now.

OaklandNS

Meter is a brand new (installed in December as part of this renovation separating the property into two units) monster rated for 475,000 btus. Alan is coming by today to test the pressure, so we'll see what happens! (he thinks it's probably the corrugated tubing).

Le John

@OaklandNS did you ever resolve the multiple ignition issue?

OaklandNS

I did not solve the multiple ignition issue. Here's what happened.

Alan F. came by and we observed that the gas pressure would start at about 11" static and drop to 6.9" on high fire. It was too much. So i called the utility and they came by, tested the pressure, didn't pay attention, didn't listen to a word I said and told me everything was fine. Since we were at the end of the heating system and I was busy, I didn't mess with it again over the summer.

More recently, I had the utility come back and was very insistent that my boiler was not designed to work with a 4" drop and that it must be an issue with the utility's regulator. Lots of back and forth, lots of 'you don't know what you're talking about,' and then the tech says,

Tech: "There's 10" static and 7" under load, that's correct for this type of slam-shut regulator." [which is true, that is the manufacturer spec for a slam-shut regulator]

Me: "Well, what does the other type of regulator do?"

Tech: "7.5 inches static and 7.0" under load."

Me: "I want that one."

Tech: "No way my supervisor will approve it, your regulator works fine."

*Calls supervisor*

Tech: "We'll switch out the regulator tonight. The supervisor knew exactly what you were talking about."

Anyway, the gas pressure is now very good. It is measuring 7.8" at the valve and drops about 1/2" when it fires up under "service" conditions (modulates rapidly to 100%). But it STILL misfires when a normal call for heat comes. So more troubleshooting for me!

Alan (California Radiant) Forbes

Have you checked the igniter?

OaklandNS

Checked the igniter and flame sensor, and both look OK to me.
I cleaned them a bit (and the gasket broke in the process). I've replaced the gasket.

I am thinking it's a low-fire combustion issue. Here's a video I made of what's going on in the heat exchanger when it trips up and cycles. You can see it ignites at medium-fire, and then as it ramps down it goes out at the very low-end. I picked up a combustion analyzer today from a lending library and I will try to dial in the low-fire settings.

https://photos.app.goo.gl/M6JbovhWitf2xdnP8

OaklandNS

I believe this is fixed, and it was an issue with low-fire combustion.

When I did the original combustion analysis last year, I used the service manual that came with my unit and it provided no provision for adjusting low-fire combustion. It appears that the service manual has since been updated on Lochinvar's website to recommend adjusting the offset on the gas valve by very minor amounts to dial in low-fire combustion, and this worked well for me. Once I got both high and low-fire CO2 and O2 levels right at the recommended targets, I was able to run the boiler through ignition and modulation to low-fire without the "groaning" and cycling I had been experiencing. The instructions in the updated service manual were clear and easy to follow.

Thanks to Boon who responded to my DM asking about a similar experience he had with his Lochinvar and thanks again to Alan F. for coming by with his manometer.

DZoro

Good to hear! Also good to hear they did a upgrade with the O/M. I know they want us to be extremely careful with the low fire adjustments and can only do them after high fire has been properly adjusted along with the gas pressure. Have worked with the Lochinvar techs, over the last few years, and they were willing to share the proper techniques to adjusting to proper levels. They also say that the CSST has nothing to do with the noise, and can tune the boiler from that happening. I know others will disagree but personally have tuned out any of those noises. Lochinvar is a class A company to work with.
Nothing can be properly done without a analyzer and gas pressure meter. These are too complex of machines, and too expensive not to be properly set up on day one.
Installing a new one tomorrow, cant wait to check out the new manual!

D

OaklandNS

Good point on gas pressure. For anyone who doesn't want to read the whole thread, I made sure my gas pressure was within the recommended ranges, including pressure drop on ignition, before I adjusted the combustion settings. That order of operations is also in the manuals.

Le John

Thanks for the info @OaklandNS. I noticed that Lochinvar has also updated the manual for the Noble Combi boiler.

SweatHog

@OaklandNS. So just to confirm: This fix required the gas company to install a new pressure regulator as well as you adjusting the offset on the Lochinvar gas valve? I have the same issue, I believe, although it mostly happens with DHW calls.

OaklandNS

@SweatHog. That's more or less right. The first thing we did was measure the pressure at the boiler's gas valve following the manual instructions to measure pressure drop during the initial firing. The regulator installed by the gas company (this was a new install with a new model called a slam-shut) wasn't within Lochinvar's specs because it is designed to drop from a static 10" WC to 7" of WC under flow. Once the regulator was replaced with the more commonly used Honeywell model, the pressure at the boiler's valve was within spec. Then I adjusted the combustion settings and everything seems to be working.

That said, you may not have a problem with your gas line pressure, and if you do it could also be the pipe sizing and is not necessarily going to be a regulator issue. I think the process is to get the gas pressure dialed in by addressing whatever the issue may be and then to dial in the combustion settings.

SweatHog

@OaklandNS. OK. Thanks very much for clearing that up for me.

Alan (California Radiant) Forbes

@OaklandNS. Good job on your sleuthing skills and tenacity!