Lochinvar Knight Boiler Flame Fail Ignition Errors - ready to pull my hair out

Teemok

You are seeing a near 1" pressure drop at full fire but………you are running lean. That high fire pressure drop reading isn't valid because and until you are burning in spec. at high fire. The difference between high and low fire might be a bias adjustment issue. Has the bias screw been messed with? A slight turn either way results in big changes. I wouldn't mess with bias until I was sure the gas volume for high fire is available. High fire o2/co2 is set first. Then low fire is dialed in via bias if necessary. Then re-test high fire, adjust and return low to check low fire. Use very small bias adjustments 1/8-1/16 of a turn. Back and forth high fire to low. (high fire = throttle adjustment) (low fire = tiny bias adjustment) until they are very close, low fire being 0.5% co2 lower/leaner. When the bias is way out of adjustment Lochinvar tech support will often just insist you get a new gas valve and start fresh. The valves can be damaged. I have brought them back into tune but it requires good logic and lots of re-testing. I've also wasted time on broken valves.

Ajmal

thanks for the feedback - I’m regards to the pressure drop, I’m going to have someone come and replace the flex pipe with 10 ft of steel pipe this week (per the manuals recommendation).

I did adjust the bias bc someone here had mentioned to adjust low fire first and then high fire - so I adjusted the bias to get the low fire in spec but when I tried to adjust the high fire after, it won’t go up any more.

So what’s the right thing to do here, of course have the flex line replaced first, and then is there a way to get the combustion back in tune? I thought the high fire wasn’t effected by the bias adjustment? Do I need to adjust the bias while on high fire to get it closer to spec?

Lastly, it does turn on, fire and work like it should now, should I not use it - I mean is it dangerous with the combustion specs as is?

Teemok

Lochinvar service manual:

Teemok

I recommend recording every adjustment. If you know how much and which way you turned the bias, I would turn it back if it was the factory setting before you adjusted it. Then dial in high fire with the trottle. Of course, this is after the gas volume changes are done. After high fire is set then tune low with bias. If the bias is way out, the boiler might lose flame when you modulate it down to low fire. You know the bias is right when low fire co2 is 0.5% leaner/lower than high fire. Think about the bias adjustment as moving along a bell curve. Turn one way and you move left on the bell and the the other way moves to the right. There is a correct side of the peak of the bell curve you want to be on. That is the side that makes low fire leaner than high fire. Exact peak of the bell curve makes high and low fire close to the same.

The manual: https://www.lochinvar.com/lit/898871100305187_2000558071_Rev%20B_WHB%20Service%20Manual%20(34309).pdf

Teemok

Notice the CO (carbon monoxide) peak on the excess fuel side. You don't want high CO.

Teemok

Notice you can get an at spec CO2 reading on either side of stoichiometric but when it's on the rich side the CO is elevated. When the CO2 reading is on the correct side (lean or extra air) the CO is very low.

Ajmal

thank you for all that information - that was really helpful in understanding what is happening. I think the bias was adjust by 2 techs previous to me working on it so i don't know what they did exactly to get it back to factory spec.

The CO levels are low on my readings so I believe I'm on the right side of the curve. The question though, now, is how do I get back to where I was. Adjusting the throttle adjustment does nothing for the high fire - do I need to put the unit in high fire and adjust the bias to get the levels back to normal?

Teemok

Is the heat exchanger clean and clear? A clogged HX can't be tuned. Gas supply volume is the first thing to address. If the boiler can't get the gas it needs for high fire, there's no gas valve adjustment that will compensate for or correct that condition. A skilled boiler tech on site looks at all the factors involved to make sense of what they are seeing, hearing and measuring. Supply regulators close to the appliance can cause problems. Restrictive gas piping, excess equivalent flue length, heat exchanger condition, etc. The bias adjustment effects both high and low fire. It is very difficult to correctly advise you as to what you must do to bring it back into tune. I have no idea how far it is from stock now or if the gas valve has be broken from being adjusted way out of range. This work requires knowledge of the product, correct use of tools and a good understanding of procedure. It's hard enough in person. It should not be done remotely.