Lochinvar Knight XL - KNB600

JStar

Two identical boilers in the mechanical room. Both are for heat. Only one does the DHW. Ongoing issues with the DHW boiler. I'll call this the bad unit. I get there today to find an ignition lock-out. Goes through pre-purge. Switches make. Igniter is sparking. Good ground. 24 volts to gas valve, hear the valve click. 2 seconds later, it drops out. No flame at all. Manometer on outlet of valve never moves from zero after the gas valve opens. Heat exchanger is clean. Intake/exhaust are clean and free of blockage (the previous month had us cleaning rocks and a McDonald's bag out of the exhaust). I even completely disconnected the intake/exhaust from the boiler. You can smell gas when the blower starts, but no flame. I switch the gas valve, and the control board from the working boiler. Same problem. And the good boiler still works. Then I switch the igniter and flame sensor between boilers. Start the bad unit up, and it fires without a hiccup. Unit cycles. DHW is back on for now until we can troubleshoot the bad parts some more. I go to the previously working boiler with the now "bad parts" expecting to see an ignition lock-out due to all of the faulty parts I just swapped into it. Jump it out to call for heat. Fires up. Cycles. Forehead smacked. Questions unanswered. Confusion setting in.



What am I missing?

Charlie from wmass

bad wire connection

or the flame sensor was not grounding well. Get a spare flame sensor and have it on hand, then it will run fine.

JStar

Maybe.

I have my reserve about the flame sensor only because I never actually got a flame on start-up.



I went back the next day to the other boiler room with three boilers. Same exact problem. Switched the igniter and sensor. Now only the one boiler works. I think I've narrowed it down to a spark gap issue. The igniter that is currently working has a slightly larger gap than the bad one. The ignition lock-out time is 0.8 seconds. Maybe the smaller spark just wasn't able to light the fuel mix. We have a Lochinvar rep. going there with new igniters soon. I'll find out then. Although, I had a Lochinvar service rep. with me the first day, and he didn't have an answer either.

Tim McElwain

Typical gap

should be about 1/8". This is a commercial version of the Knight and has some extra controls, which are typically a low and high pressure gas pressure switch. I would monitor the inlet and outlet gas pressure when attempting to fire. In going through the Sequence of Operation (Pages 11 and 12) of the service manual. The units 501 model and up will lockout if the second attempt fails. Does it try to do a second attempt? The flame on these units must be detected within 1 second after the sparking ends, next question does the sparking end or does it keep sparking - no flame and then lockout? 



I would also check to make sure all the parameters are set correctly according to the manual.

JStar

Operation.

The gap looked to be about 1/8" just by eye. It does lock out after two tries. The sight glass into the heat chamber is so small that I couldn't see when or if the igniter was ever sparking inside. Can you meter the ground leg on the igniter to know when it's sparking without actually seeing it? I could barely hear it over the blower noise. I checked outlet gas pressure. It starts in a negative when the blower comes on, then goes to 0 when the valve opens. When I hooked up to the inlet side, I was reading 7", but as soon as the boiler started up, I got a pressure switch fault, so I couldn't read the inlet pressure while the boiler was running. I probably have a tiny leak in my manometer hose causing the pressure switch to trip.



As for the parameters...do you think the blower is running as the wrong speed? What range should I be looking for? And why do all of the other boilers work? They are all piped and vented as close to identical as possible.

Tim McElwain

Yes it is possible

that the blower is not getting up to speed or it is set incorrectly. I am not sure if the blower speed can be changed on these units. Some systems do allow you to change blower speed.



Are you getting any kind of fault code when this happens? Also check the troubleshooting in the service manual on Lochinvars site pages 33 to 45. One thing also to check is there a "Ramp Delay" set up on this unit. I would also check to see if this is set to a Building Management System which could be set incorrectly.



As for the gas pressure issue I would recheck that as the pressure switch could be faulty or you may have a drop in gas pressure when this unit fires. Is this unit at the end of the gas line, if so it could be dropping below the settings for the pressure switch. 

Charlie from wmass

I have had animals from bugs to small

mammals and birds in blowers. also had cracked or bent blowers interferring with blowers reaching speed. All fun things to trouble shoot. did you check the intake pipe for debris?

JStar

...

Intake and exhaust are free and clear. I even had them disconnected from the boiler for a few tries.



As far as I know, all 5 boilers on site are set-up (parameters, fan speeds, etc) exactly the same way, and 3 of them have never had a problem.



I'm getting an Ignition Failure lock-out fault code. I believe it is expressed as "No Flame Ign". I have 7" W.C. on my gas inlet. It's the first boiler on the gas line in the mechanical room. Gas pipe size is correct. Other than the times when I had my manometer on the inlet side, I've never gotten any other fault codes during ignition trial.



A few guys have gone there before me. All they did was clean the flame sensor and walk away. They said it was running when they left, but who knows...

Charlie from wmass

Flame sensor then

you can clean some many times and others only once before replacing. There seems to be no rhyme or reason to which ones last and which do not. also I was told nothing harsher than a dollar bill to clean them with. If that does not clean them they need replaced.

JStar

Can"t be flame sensor.

Never got a flame.

ACME

Sr BoilerTech/ Co founder

Check your combustion readings. You may have to adjust fuel/air mix for proper light-off.

Most of these boilers like 8.9% CO2 at high fire. This unit lights of at 37% fire rate.

You will have to try turning fuel/air adjustment screw clockwise first. This process can take awhile as you will need to make small 1/8 turns on the allen hex tool.

This procedure can be done by an experienced installer or service tech versed in these types of boiler units. RC

Burnertech

a few things to check

Make sure the cap on the igniter is correct 1/8" should do. If you are sparking and not igniting you may want to access the board and remove the ignition wire from the transformer and attempt to the fire the unit. If you do not see a spark jump to the grounding post, you have a failing ignition transformer. They are integrated into the board, so you will need to replace the board.

Lochinvar_owner

I have had the same issue as JStar mentioned above. Over the years I have up kept the maintenance and yet my boiler goes out when it's -30 Celsius outside.

It's been explained to me that a small amount of condensation builds on the exhaust when it's so cold outside and flame will not ignite even though there is a spark. (I have taken everything apart and reset the lockout several times within an hour with no luck)

What I have found to be 100% successful is using a hair dryer on the exhaust to pull more air out of the exhaust. I go outside and put the intake end of the hair dryer up against the exhaust from the boiler and with the boiler cycling through it's four ignition attempts the boiler will ignite.

Seems finicky and comical for the elaborate set up I have, so my question is does anyone have a suggestion for a long term solution?

Do I need to alter the exhaust outside of the home? Currently it vents out the side, rises about two feet and then has a 90 degree elbow. When its cold outside I have a large icicle that builds up from the ground which is caused from the condensation.

Or do I need to increase the speed of the fan on the unit - not sure if that is even possible.

Zman

Has anyone done a combustion analysis? The higher air density cold air could be causing the boiler to run leaner.

Lochinvar_owner

I have not had this done since it was installed 8 years ago. The installer has said it's just a minor issue to deal with when it gets that cold and the air is more dense, however I sure don't want to leave the home knowing it will not ignite without some assistance.

Reading up on the combustion analysis some state it should be done annually under a heavy load and, others say when a component of the boiler has been changed. Any input would be appreciated.

Zman

My guess is that a combustion analysis has never been done. Can your installer provide the test results.

emfriction

I would like to note that I have worked for a large condensing boiler company in the past and the only problem I have with lochinvar that I do not with any other company is they will not give you their required pressure drop limitations for the vent and intake in inches of water column so you can prove an issue out. rather they say you can and can't do certain things within installing the intake and exhaust.

JohnNY

I don't see how a combustion analysis will help when the unit is locking out on ignition. The fan speed is settable on a Knight XL but not on ignition. It rises to, I believe, full speed and then comes down to your setting once ignition is proven.
I had a problem like this with another condensing boiler manufacturer and they advised me there could be a factory issue with the spacing of the heat exchanger coils which disallowed adequate flow through to the exhaust and made the mix in the chamber to rich for combustion.
This unit also worked well when I pulled the flue piping off of it.