The case of the intermittent flame failures, this Fridays video

RayWohlfarth

There is not a case to solve this week. rather, I wanted to share the common or weird things I have found in the field that caused intermittent flame failures. If you have been doing boiler service, you have come across this jobs and they can be frustrating. I will be interested to see your comments and other things you found in the field.

Mustangman

Hey guys. I run the HVAC department of a medium sized Plumbing and heating company. I typically don't get called out unless the guys are struggling. Seems like there has been a run on flame failures. We had one a few weeks ago that I fixed purely by accident. The call was occasional flame failure. This was a 80+ draft induced gas furnace. I was getting really odd voltages. Where I should have 120V I was getting 75 volts AC. My secondary on the transformer was well under 24V. My first thought was my Fieldpiece meter was acting up. All the sudden, the furnace came on and ran flawlessly for 1/2 hour. Thermostat was satisfied. We gave it some time and bumped up the stat. Inducer motor came on, no flame and the worst part, no error code. As I was scratching my head and fending off questions from my tec, I noticed that this basement had a serious moisture problem. Anything steel was rusting. In the corner was a dehumidfier not operating. It hit me what if this is not a furnace issue but a power issue. I stumbled across the basement, climbing over the homeowners property and finally made it to the panel box. I opened the panel box door and at the same time, the furnace comes on.. and lights. I went back and checked the areas I had low voltage and I had normal readings. So at this point, I knew the issue was not furnace. I took off the panel cover and you could see the high moisture was effecting inside the box too. Breaker 14 was my problem child. First, the connection screw was far from tight and the wire was dull and a bit corroded. I pulled the breaker and you could see the 2 buss bars showed signs of corrosion too. Not having a 20A Eaton we cleaned it and it took off and ran flawlessly. I had my guy change the breaker. I have not heard from the customer since. Good luck
Steve Noviello.

EBEBRATT-Ed

I could post hundreds of stories and they are all true. I will just post 3 of them.

Prior to 1980s the older primary controls (and I am talking commercial burners here) if a low water cutoff or some other control short cycled the burner really quick the older mechanical primaries would just shut the burner down and recycle it. When the new solid-state primaries came out a short cycle ended up as a Flame Failure sometimes.

On one job with a gas oil burner, we had lockouts at least once a day. My best tech and myself worked on this several times. The maintenance man reported it locked out usually in the morning.

I went there and sat in a chair early in the morning and the burner started coming out of night setback. It ran sever cycles shutting down on steam pressure and restarted normally. Finally, the thermostat reached set point and I waited. By this time the employees were in the office building upstairs. After a while the burner started and ran a little the thermostat relay on the wall chattered and the burner locked out. The thermostat that ran the relay was mounted on the all next to the men's room. The mens room door had a defective closer and was a heavy door. It was a mercury stat. If the building was near set point the slamming door would rattle the mercury and short cycle the burner locking it out.

Another one that happened several time was with commercial burners using a lead sulfide flame detector. We would have random lock outs. If the combustion chamber was hot and the burner started the compressed air going through the nozzle on pre purge would set up a false flame condition because the detector was looking a glowing hot refractory through the air mist.

The third was caused but a somewhat lower than normal voltage. We had burners that ran fine for extended periods of time and then get very random lockouts. In some cases the problem was low voltage. While voltage is supposed to be within 10% of the equipment name plate (high or low) and all devices now are rated for 120 v this means you need 108-132v

But many don't realize that if your say 8% low that means your flame signal will be 8% low and your ignition transformer will be 8% low on it's output voltage. This can be enough to cause problems. In my experience anything below 110 is suspect if your having problems

a typical 120-6000 volt ignition transformer will only output5520 if you feed it with 108 volts

RayWohlfarth

Thanks @Mustangman and @EBEBRATT-Ed I think every tech has their favorite "Intermittent Flame Failure Horror" stories They made us better technicians. Here is the link to this weeks video https://youtube.com/watch?v=KBW0cpa8OBw