Flame Sensor Hack?

[toyrist]

Hello DIY,

Gas unit: 1988 Janitrol Goodman GUI 125-4 rev s   input 125,000

I had an issue with my gas heat unit not turning on. I proceeded to clean the flame sensor, and the unit responded somewhat but it was still having problems detecting the flame from the pilot. The flame from the pilot has always turned on and that does not seem to be the problem. I initially thought that the flame sensor was dirty so I cleaned it, nothing. Thought it was defective so I bought a new one, nothing. The new one did not worked as expected either. I started investigating more and inspecting the unit and realized that if I moved the flame sensor closer to the pilot flame (actually getting it off the intended place and manually putting it close to the flame), the unit would go thru the motions normally (turn on main gas, etc). It seems that the flame from the flame sensor is not "spreading" enough to activate the flame sensor at the distance it was designed for. Now this unit is old (30 years) and rusty. It worked for two winters without a glitch since I moved to this old house. This is the third year and it is when it is giving me trouble.

So what I did was to bend the flame sensor with pliers to have it closer to the flame (see pictures). I bent the old sensor and voila! the heater unit is now sensing the pilot flame and turning on the main gas immediately after. blower turns on, etc.

Pictures:
the one one the right is the stock photo of my pilot and flame sensor (circle red notice the gap between sensor and flame).
the one on the left is my system before I bent the sensor (was working for 2 years, stopped working this year)
the one on the bottom is bent flame sensor (working now)


http://imageshack.com/a/img921/6711/O0ggcf.png



Questions:

(1) is the flame sensor capable of withstanding being closer to the pilot flame, heatwise or otherwise? I would suppose so since the flame sensor is next to the main flames once the unit goes on. it does get hot in there.

(2) is the flame sensor too close to the flame that it can "overheat" the electronics on the other side of the flame sensor? It is literally touching the pilot flame once the thermostat turn it on.

(3) i thought flame sensors were delicate. I bent and mistreated the old one and is working. I had also cleaned it with a fine wire cloth (didn't work) and to an extreme scrapped it with a blade a lot beforehand trying to clean it (back when I thought the sensor was dirty). The old sensor is really beat up. How come is still working?

(4) how come the flame heat from the pilot is not "reaching" the flame sensor any more to turn on main gas? Is the pilot system somehow "plugged"? It definitely worked without a hitch for the last two years. How come it got "plugged" this year?

(5) any other comments?

Thank you guys,

TL;DR: bent my flame sensor so it is able to detect pilot flame. is my unit going to blow up? Look at picture

[sirdoug007]

This is a very bad idea.

The flame detector is a critical component to positively identifying a flame and stopping gas flow if there is not a flame.

By modifying the flame detector you are at risk of the main not lighting and putting lots of unlit gas into your house which could cause a massive explosion.

Please get a professional to inspect your furnace!


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[BudgetSlasher]

That is not a setup I would do.

It looks like it is a flame rod (do you know if that is correct), which as I understand it works by passing electricity (not heat from the flame) across the flame itself. So the rod would have to be in contact with the flame. Seeing as how the system works when you move the rod closer that would seem to indicate that the rest of the system, electrical and computers, is working fine; that leads me to believe that, contrary to what you say, the pilot light is the problem. Perhaps the flame is not as large or clean burning as it used to be.

So, by moving the sensor you are allowing the system to potentially operate with a smaller pilot light . . . which if ignition fails or is delayed might not be pretty.

As to your questions.

1) If it is a flame rod, it is supposed to be in contact with the flame and can take the heat.

2) See above.

3) If it is a flame rod style sensor then it is literally just a piece of metal that conducts electricity.

4) You are asking why a 30 year old system that looks well worn and rusted chose this year to fail? If I had to guess it is well worn and rusted, it might have sat all summer and condensation formed more rust, something bumped into it and knocked some rust loose and obstructed the gas flow, and to top off it sounds like it probably hasn't seen any kind of preventative maintenance or servicing in a few years.

5) Your "hack" is nothing more than bypassing a safety feature, period, full stop. You need to get to the root of why the pilot light is not reaching the flame sensor. Judging from the shape of the pilot light it looks like the whole assembly is probably due to be replaced. It sounds like now would be a good time to have a professional come out and perform a service/tuneup to fix this issue and determine if there are any other issues that need to be addressed in the near term.

[TomTX]

Time for a professional overhaul or replacement.

[BudgetSlasher]

A little off topic.

With any combustion device, you should have a CO (carbon monoxide detector), but with a 30 year old unit you definitely need them. For your own safety, if you don't already have them, please install some near the furnace and near bedrooms.

Given your "hack" may I suggest a combination CO and explosive gas detector?

[fwttg]

I'm no gas fitter so this is in no way professional advice, just passing on my experience.

The other posters may be correct with their concerns. You will have to decide.

In my situation I suspected and replaced the flame sensor without success.

The problem turned out to be some junk obstructing the orifice of the pilot light supply. Not sure if it was scaling or debris delivered with the gas.

Disassembling the line and and fittings and tapping, shaking, blowing, etc. dislodged a bunch of junk. The pilot light was much stronger after reassembling. It has been working fine since.

Obviously (I hope), turn off the gas before proceeding if you decide to attempt this.  Allow time for gas to dissipate before testing.