# How to confirm 2nd stage burner working?



## yuri (Nov 29, 2008)

They should open that box and inspect the burners and clean the flame sensor and see if any debris/leaves/bugs got sucked into there. It is under negative pressure and I have seen none of them sealed with RTV silicone. The air temp may be the same on high fire as low fire as the fan will speed up when it goes to high fire. I would have the tech meter clock the furnace to make sure it goes to high fire and/or check it electrically. In the owners/installers manual there may be a meter clock chart which you can follow. Basically you look at the chart/find a 1 cu.ft dial on the gas meter and count the seconds for the dial to make one revolution and compare them to the chart to determine the firing rate. The firing rate is on the model # sticker.


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## beenthere (Oct 11, 2008)

They should open it and do as Yuri said.

You can look at your gas meter when you know its in low fire.
Then turn your stat up and waut for the blower to increase speed, then look for yourself if the gas meter has increased in speed.

Its possible that the gas valves regulator isn't letting as much gas through as it should.

So they should also check the manifold pressure of both stages of heat.


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## yuri (Nov 29, 2008)

Good points. Have them check the small 1/4' hoses from the gas valve to the burner box etc. Those hoses will regulate the gas valve pressure. Make sure they use a manometer to check both gas pressures low/high fire. Ask the company to send an experienced tech who has/knows how to use a manometer. Lots of newbies/hackers don't.


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## mirob (Dec 26, 2008)

Thank you yuri and beenthere for your replies. I appreciate it. I will do the gas meter thing first and if it increases gas usage I'll assume its working ok.

Thanks again!


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## key1cc (Nov 21, 2008)

yuri said:


> . I would have the tech meter clock the furnace to make sure it goes to high fire and/or check it electrically. In the owners/installers manual there may be a meter clock chart which you can follow. Basically you look at the chart/find a 1 cu.ft dial on the gas meter and count the seconds for the dial to make one revolution and compare them to the chart to determine the firing rate. The firing rate is on the model # sticker.


Good insight.
I think I'll check this also just for confirmation. One question. My instructions has a chart that provides gas flow in cubic feet per hour (CFH) which I can figure out by timing the revolutions on my gas meter.

However, I am supposed to multiply this CFH number by the "heating value" of the gas obtained from the utility company. Is that "heating value" the Therms? My PSE&G bill provides me Therms and CCF (whatever that is).

Thanks for your help.

Key1


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## yuri (Nov 29, 2008)

Here is the chart I use. The firing rate ie: 36 =36,000 BTU's/hr. THe gas htg value varies slighty but is not a major concern.


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## key1cc (Nov 21, 2008)

yuri said:


> Here is the chart I use. The firing rate ie: 36 =36,000 BTU's/hr. THe gas htg value varies slighty but is not a major concern.


Thanks, my data below is very similar but on a 2 cubic foot dial.

Key1


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## yuri (Nov 29, 2008)

It helps to use a stopwatch/repeat the process 3 X and average the results. Make sure the water heater or no other appliances are running at the same time.

Good Luck


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## key1cc (Nov 21, 2008)

yuri said:


> It helps to use a stopwatch/repeat the process 3 X and average the results. Make sure the water heater or no other appliances are running at the same time.
> 
> Good Luck


All done :thumbsup:

My gas meter had the 1/2 cubit foot dial so I divided my flow number by 4 as instructed. I measured 4 times. twice I got 29 seconds and twice I got 31 seconds. If I believe the 29 I get a value of 62 (which I presume implys 62,000 BTU.). If I believe the 31, I get a value of 58 which implys 58,000 BTU. Soooo my furnace in stage 1 is using somewhere between 58,000 and 62,000 BTU. I have a Trane XV95 2 stage unit rated at 100k btu input 2nd stage and 65k btu input in 1st stage.

looks like I'm low.....not sure what it means though.

Key1


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## yuri (Nov 29, 2008)

60,000 sounds about right for the 1st stage. If you have a true 2 stage tstat with a wire connected to a W2 on the tstat and the circuit board then it should shift into 2nd stage if you increase the temp by more than 1-2 degF. If using a single stage tstat then the board will have a timer of 7-15 minutes (I am not sure about Trane's timing) before it goes into 2nd stage. It should take awhile B4 it goes thru its timer and then you need to meter clock it again. Depends on how the installer setup the dip switches on the circuit board. Try it again after 10 mins of running on low fire. Some of our other guys may be more familiar with that unit and know the timing biz. I am mostly a Lennox/Carrier guy. That info may be in the installation manual.


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## beenthere (Oct 11, 2008)

Your 3000 to 7000 BTUs light in low fire.

Another thing your original installer didn't set up.


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## key1cc (Nov 21, 2008)

beenthere said:


> Your 3000 to 7000 BTUs light in low fire.
> 
> Another thing your original installer didn't set up.


 
I am not suprised.
...being that this is the DIY site.
How might one go about correcting this BTU deficet? 

Key1


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## integlikewhoa (Dec 31, 2007)

I also have an XV95 (smaller unit tho 52k,80k btu's). I'm not sure if yours is an upflow like mine also, but asuming yours is (I think downflow btu #'s are the same anyways) you should have part number TUH2C100A9V4VA

Look at page 6 of this trane manual for upflow and page 7 for down flow #'s
http://www.trane.com/webcache/un/furnaces%20(furn)/product/22-1814-02_01012008.pdf

The rated input is 65,000 btu but the actual is 61,750btu. This puts you right where you should be for your first stage. 

Same goes for the 2nd stage. Its rated for 100,000btu but actual is 95,000btu. 

The #3 next to the numbers says "Based on U.S. government standard tests."

Also altitude will play into this to some degree. So I think your fine on your findings for stage one. Now lest test stage 2. Crank that t-stat to 90 degrees inside and see what she can do.


Edit: I did check and the down flow BTU's are the same readings so either way 61,750btu acutal is the correct number for which ever model VX95 you have.


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## beenthere (Oct 11, 2008)

integlikewhoa said:


> Look at page 6 of this trane manual for upflow and page 7 for down flow #'s
> http://www.trane.com/webcache/un/furnaces%20(furn)/product/22-1814-02_01012008.pdf
> 
> The rated input is 65,000 btu but the actual is 61,750btu. This puts you right where you should be for your first stage.
> ...


What your calling actual, is the output.

But to get that output, you must have the higher input.

EG: Input of 65,000 BTUs times 95% efficiency = 61,750 BTUs output.


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## beenthere (Oct 11, 2008)

key1cc said:


> I am not suprised.
> ...being that this is the DIY site.
> How might one go about correcting this BTU deficet?
> 
> Key1


Need a manometer, to connect to the manifold side of the gas valve.

Once you have one and connect it(need 1/4"MIP to what ever size hose barb fitting). 
Run the furnace in low fire, and adjust the gas pressure to I believe its 1.6" for Trane in first stage(check installers manual).

Also, you need to pull off teh hose that runs from the gas valve to the burner box, and remove teh burner cover plate.

Be carefull not to damage plate seal.

Also, you must then check the gas pessure in high fire. And then recheck low fire. Adjustment of one does effect the other.


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## integlikewhoa (Dec 31, 2007)

beenthere said:


> What your calling actual, is the output.
> 
> But to get that output, you must have the higher input.
> 
> EG: Input of 65,000 BTUs times 95% efficiency = 61,750 BTUs output.


DUH :wallbash: 

Makes more sense now. Thanks for the clear up.


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## yuri (Nov 29, 2008)

Was reading the Lennox info and apparently you are supposed to multiply the reading by the htg value of the fuel to be more accurate. Around here it is supposed to be 1050-1100 / cu.ft so that would bump up our posters results. As a rule of thumb I usually use the chart X 1000 to get close enough. I also use a manometer to check the actual gas pressures. The gas valve will modulate slightly with the draft thru the heat exchanger/hose from the burner box does that job to compensate for the venting.


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## integlikewhoa (Dec 31, 2007)

It still sounds like hes going to be good for stage one of heating, but I'm waiting to see what he comes back with for stage 2. Should be easy enough to tell if it goes up quiet a bit.


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## key1cc (Nov 21, 2008)

I just switched her to 2nd stage and timed the meter. (again water heater, stove, and dryer all confirmed off). I repeated the measurement 4 times and twice I got 21 seconds and twice I got 19 seconds.

If 21 seconds is correct I'm low at 86000 BTU.

If 19 seconds is correct I'm right on at 95,000 BTU.

Tomorow in the day light I will recheck all using the 2 cubic foot dial instead of the 1/2 cubic foot dial....... since it moves at 1/4 the speed (much slower) it may result in a more exact measurment since 1 second makes a big difference.

Key1


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## key1cc (Nov 21, 2008)

yuri said:


> Was reading the Lennox info and apparently you are supposed to multiply the reading by the htg value of the fuel to be more accurate. Around here it is supposed to be 1050-1100 / cu.ft so that would bump up our posters results.


My Trane info states the same thing. How do you obtain the "heating value" for Princeton, NJ?

Key1


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## beenthere (Oct 11, 2008)

Call the gas company, and ask them the BTU content.


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## key1cc (Nov 21, 2008)

Well I decided to grab a flashlight and go out side and re-run the numbers using the 2 cubic foot dial for better accuracy. When I used the 0.5 cubic foot dial each measurement took 20-30 seconds so being 1 second off makes a big difference.
Using the 2 cubic foot dial each measurement took between 81 and 120 seconds so much more accurate.

Here are the results:

Stage 1, 120 seconds = 60,000 btu input
Stage 2, 81 seconds = 89,000 BTU input.

Looks like Beenthere is correct and I am short 5k BTU on stage 1 and 6k BTU on stage 2.

According to my PSE&G Bill I beleive my Heating value is 1012 so that only bumps me to 61,000 BTU and 90,000 BTU.

Key1


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## key1cc (Nov 21, 2008)

Is there a downside to being low on BTU's if my home is being sufficiently heated? I understand that it takes a given amount of BTU's to heat an area, whether it happens fast or slow.

Wouldn't this mean my furnace would just run a little longer to get the home to the set temperature? Ultimately resulting in the same BTU cost as if the furnace BTU's had been set higher?

Key1


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## yuri (Nov 29, 2008)

You are correct. Altitude and some other factors/venting/gas valve modulating will affect your readings. I would not worry about anything. It is worthwhile to get a tech to check the manifold pressures at some time.


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## beenthere (Oct 11, 2008)

It depends what your temp rise is.

If your temp rise is low. Then it could cause condensation in the primary heat exchanger. And the primary is not designed to have condensation happen in it.

2 stage units are a couple % less efficient in first stage to begin with.
So your just a bit less efficient yet with an under fired first stage.
So instead of being at 92 or 93%, you may be down to 89 or 90% in first stage.

Check your temp rise.
Then do the math.
(temp rise times 1.08) times CFM equals BTU output.
See what it says.


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## key1cc (Nov 21, 2008)

beenthere said:


> It depends what your temp rise is.
> 
> If your temp rise is low. Then it could cause condensation in the primary heat exchanger. And the primary is not designed to have condensation happen in it.
> 
> ...


Temp Rise = 48Fx1.08x1180CFM=61000BTU

Key1


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## key1cc (Nov 21, 2008)

beenthere said:


> .....So instead of being at 92 or 93%, you may be down to 89 or 90% in first stage.


Please clarify.:confused1:

I thought that my 95% AFUE furnace utilizes 95% of whatever amount of gas that goes through it. If 65000 BTU's went through it, would it not utilize 95% of the 65000 and have 61750 output??
However if 60,000 btu's went through it, the furnace would only utilize ~90% of the 60,000 (or 54000 BTUs) ??? Why would it not utilize 95% of the 60,000??

Key1


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## beenthere (Oct 11, 2008)

Less gas, means less radiant heat transfered to the heat exchanger.

Cooler heat exchanger means it puts off less radiant heat to the jacket/insulation foil face. So less BTU transfer.




PS: Don't check temp rise directly above the heat exchanger.
The thermal probe can pick up radiant heat, and give you a false higher temp reading.
Should be taken in the trunk line, out of sight of the heat exchanger.


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## key1cc (Nov 21, 2008)

beenthere said:


> PS: Don't check temp rise directly above the heat exchanger.
> The thermal probe can pick up radiant heat, and give you a false higher temp reading.
> Should be taken in the trunk line, out of sight of the heat exchanger.


I check temp rise in the plenum above the coil. Is that too close to the heat exchanager?

Key1


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## beenthere (Oct 11, 2008)

That should be ok.


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## key1cc (Nov 21, 2008)

beenthere said:


> It depends what your temp rise is.
> 
> If your temp rise is low. Then it could cause condensation in the primary heat exchanger. And the primary is not designed to have condensation happen in it.


My installation instructions state that my temp rise range is 35-65F.
So it looks like I am ok at 48F.

Key1


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## key1cc (Nov 21, 2008)

After rechecking......

my 48F Temp rise occurred with my humidifier bypass open. I believe it should be done with the bypass closed, correct? If that is the case, then the temp rise with the bypass closed if 45.3F

45.3x1.08x1180CFM= 57,730 BTU's output .....confirming what Beenthere indicated, that I am low on BTU's.

I will now look into what is required (special tools) to increase the gas pressure to bring the BTU's up to the stated value.

Key1


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## key1cc (Nov 21, 2008)

Well, I read the installation manual on checking/changing the gas manifold pressure. Considering I am accustomed to dealing with gas (installed gas fire place, gas ovens, gas dryers,etc) I am not to intimidated. 

It looks very straight forward. My current magnehelic guage only goes up to 1.0 W.C. so I need to wait until I get one that goes to at least 4 W.C. since my unit calls for a 1.7" W.C. Max. for 1st stage and 3.5" W.C. Max. for 2nd stage. Here are some pics below. You may notice the "hi" and "Lo" gold screws for seperate independent adjustment of 1st stage and 2nd stage in picture 1.

Key1


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## beenthere (Oct 11, 2008)

Yea, the humidifier bypass being open, give a false temp rise.


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## beenthere (Oct 11, 2008)

Although they are independant adjustments.
When you change one, it influences the other.

Don't forget to pull the hose off the gas valve, and remove teh burner box cover plate.


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## key1cc (Nov 21, 2008)

beenthere said:


> Although they are independant adjustments.
> When you change one, it influences the other.
> 
> Don't forget to pull the hose off the gas valve, and remove teh burner box cover plate.


Ok, thanks.

I have a real non-pro question for you.

Why can't I just adjust the screws ~ 1/2 turn at a time, then close the unit up, cut her on and recheck the temp rise and also re-time the gas meter to see the impact of the adjustment (since I don't have the pressure gauge yet)?

Key1


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## key1cc (Nov 21, 2008)

beenthere said:


> Don't forget to pull the hose off the gas valve, and remove teh burner box cover plate.


My installation instructions states that I should pull the hose at the "T" and then "T" in a manometer....but it also states I do not need to pull the burner box cover plate for this model unless I plan to adjust the flame sensor, hot surface igniter, or main burner orifices..

Key1


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## beenthere (Oct 11, 2008)

If you get a dual port manometer, you don't need to pull the cover, if you tee in.

Doing it by checking temp rise and reclocking the meter.

Assumes that the air flow is exactly XXXX CFM, and that the thermometer used is 100% accurate.

Reclocking the meter is good. But, you don't know the true BTU content of the gas.

If the CFM is slightly lower, and the thermometer reads high temps higher then they are, then the gas pressure would still be low.

The difference between 1325CFM and 1265CFM is roughly 2°F at 61,750BTUs output.

Even VS motor CFMs can be off compared to the factory chart/listing.


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## key1cc (Nov 21, 2008)

beenthere said:


> If you get a dual port manometer, you don't need to pull the cover, if you tee in.
> 
> Doing it by checking temp rise and reclocking the meter.
> 
> ...


Thanks,
Makes sense.
I'll order the manometer through the net.

Key


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## key1cc (Nov 21, 2008)

Also,
It is interesting that the pressure max is 1.7" for stage 1 regardless of the gas heat value. If I set it to 1.7" the final BTU's will still depend on the heat value of the gas.

Question: If the manifold pressure turns out to be low say around 1.4"....what is wrong with adjusting it to say 1.9 or 2.0 (instead of the stated max of 1.7) to get even more BTU's for more efficiency (in stage 1 only) as long as my temp-rise does not exceed the 65F max?

Is this something "Jim Davis" would promote?

Key1


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## beenthere (Oct 11, 2008)

I believe he would. But, he would be using an annalyzer to check other things also.

One of the problems is that next month. The BTU content could be higher then this month.
So you would have a much hotter heat exchanger. And may be above allowable temp rise.

Next, is that the inducer only moves so much air and gas through the cells in first stage. You would end up with poor combustion.
High CO, low CO2, and low O2. Giving you incomplete combustion.

Meaning, although you inreased BTU output. You had to increase BTU input to an amount that your only at maybe 87% to 88% efficient.

So your input may be 74,750, to get 65,000. (86.9% efficient)

Next. The top of the heat exchanger would begin to over heat. 
If it failed. Trane would be able to see the heat distortion. And could void warranty on it. 

Even if its within temp rise. The burner end of the cells, will get hotter then they should.

The manufacturers, know what a over heated HX looks like.

Keep in mind, that mod furnaces vary both the inducer speed and blower speed with the gas input, to avoid this problem.


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## yuri (Nov 29, 2008)

"Turning" those screws is a very precise process. May only need 1/16-1/8 of a turn to make a BIG difference. Has to be done with a manometer. After you turn the screw you need to put the cap back on and then check the reading, or put your thumb over the screw port. There is no packing around the screw and pressure may leak past it and affect the reading. Good thing you have some Pro's here to walk you thru it. Soon you will know more than some of the hackers out there. This is one of the 2 manometers I use. Has a great magnet on the back to hold it to the furnace housing. http://www.ueitest.com/product-em200.html
The other one is this one. More expensive but incredibly accurate and fits in small places.http://www.etool.ca/RENDER/1/11/3041/10955.html
Good Luck


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## key1cc (Nov 21, 2008)

yuri said:


> "Turning" those screws is a very precise process. May only need 1/16-1/8 of a turn to make a BIG difference. Has to be done with a manometer. After you turn the screw you need to put the cap back on and then check the reading, or put your thumb over the screw port. There is no packing around the screw and pressure may leak past it and affect the reading. Good thing you have some Pro's here to walk you thru it. Soon you will know more than some of the hackers out there. This is one of the 2 manometers I use. Has a great magnet on the back to hold it to the furnace housing. http://www.ueitest.com/product-em200.html
> The other one is this one. More expensive but incredibly accurate and fits in small places.http://www.etool.ca/RENDER/1/11/3041/10955.html
> Good Luck


Thanks for sharing. The 1st one is listed at $153 on amazon.com and the 2nd one list the price as ~$232. You are correct they are expensive for someone not currently in the trade. However, I look at it this way. I saved at least 3 thousand bucks by not purchasing the 10 year labor warranty from the hacks that installed my system. It's a long story that I shared on another site but basically, I had wiring issues, equipment oversized, static pressure issues, leaks, etc. My system already comes with a 10 year parts warranty. The installer wanted an additional $1000 bucks for a 10 year labor warranty and it would only remain valid if I paid them $200+ bucks every year to "maintainence" my system. That totals over $3000 bucks for the ten year period! Why would I pay these hacks that kind of loot, when they could not even get the initial install right, nor correct the problems? Thanks to sites like this and help from knowledgeble pro's like yourself and Beenthere (among others) I have learned quite a bit and already have a pretty good understanding of my system. A few hundred bucks for tools and spending time on the net for knowledge is a small price to pay from my vantage point.

Key1


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## key1cc (Nov 21, 2008)

beenthere said:


> I believe he would. But, he would be using an annalyzer to check other things also.
> 
> One of the problems is that next month. The BTU content could be higher then this month.......
> 
> .....Next, is that the inducer only moves so much air and gas through the cells in first stage. You would end up with poor combustion......


Gotcha. 

Thanks for the feedback.

Key1


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## hvaclover (Oct 2, 2008)

beenthere said:


> It depends what your temp rise is.
> 
> If your temp rise is low. Then it could cause condensation in the primary heat exchanger. And the primary is not designed to have condensation happen in it.
> 
> ...


Don't even go there Been! The pro forum is still arguing that point and I think the thread post count has exceeded *4789!

LOL!
*


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## beenthere (Oct 11, 2008)

LOL...

But it was a good thread. 

Did you check out the evacuation thread yet.


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## hvaclover (Oct 2, 2008)

beenthere said:


> LOL...
> 
> But it was a good thread.
> 
> Did you check out the evacuation thread yet.


No. What pro forum was it in?


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## beenthere (Oct 11, 2008)

Pro tech.


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## yuri (Nov 29, 2008)

A fella can never have too many tools! or toys. You may need it someday if you have a pressure switch problem or other issues. The Testo one is especially good for pressure switches.


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