Robertshaw SP 735 A ignition control

[Anthony Diodati]

Hi, l wonder if I could run this by you. We have a furnace made by Armstrong ,its an ultra II ,EG6E-and EG7E ,it is about 10 0r 11 years old. Last winter the furnace went out, and when the T/Stat was turned up, the blower would kick on, but the burner would not come on. I found the combustion blower to be real hot to the touch. Also I could see it was not running. If I supplied a vacuum to the pressure switch, the ignition control would become energized, and would light the pilot, the burner would fire. It was fine all last winter and all this winter, till today, I was roasting, so I set the T/Stat down to about 65 degrees. I came home and noticed it was getting cold , recalling I had lowered the T stat, turned it up to about 70 degrees. Having had only a few hour's sleep the night before, I laid down for a nap about 7:00 PM. About 2 hours later The wife awakened me, stating the house was cold, and the furnace was not kicking on. She had removed the cover and said the burner was not firing. I shut the T/S down to it's lowest temp, and went to the basement, removed the cover, and had her kick up the t stat. The was running just fine, and tested the pressure switch(SWITCH SIDE) with an ohm meter, and it was closed. The pilot was not lighting at this point, so I took a Light stick and taped the ignition control lightly and the "electric spark" (?)started ticking, and the pilot lit and soon the burner fired. We kept the t/Stat up to 80 degrees for a while, but the thermometer(sp) was only reading about 68 degrees. Well I had to tap on the ignition control a few more times tonight,but I am roasting again, so it seems to be working"for Now" I just lowered the T/stat to 68 degrees about 15 minutes ago, and just now set it up to 71 0r 72 degrees, and went down, and the "burner is burning". So, If I start having problems again, Replace the Robertshaw SP 735 A ignition control ?? About how costly is this Item. Thank You, Tony D.

[Anthony Diodati]

I found the combustion blower to be real hot to the touch. Also I

*** I replaced The combustion blower *******

thermometer(sp)

[CBhvac]

Gonna tell you a couple of things... First, twisting that thermostat isnt doing anything.....nothing. It is an ON, OFF switch and cranking it to one extreme to another is nothing but a time waster for you..but if it makes you feel good..whatever. Most people pick a temp and leave it....otherwise, its also a waste. Tapping on the ignition control...wow. Let me ask you something....what if you have a bad Klixon, or a bad ground? You can go replacing parts all you want, but unless you know what to look for, and where...well..nothing I tell you is going to work....Particularly on that Armstrong.

If you want to go throwing parts at it, since its almost doubtful the control module is bad...and while replacing it just might sure enough cure it, since in the process you fix the original problem, the replacement runs in my area about $145 for the part...not installed. If you can get the correct replacement for less...good... If not..sorry.

I get called out on these calls all the time, and the customer is surprised when the fix is about 5 minutes of work and under $100....and no...I doubt seriously its in the board...it might be, and if it is, I am sure you will be more than happy to tell me all about it...but I would be looking elsewhere FIRST....since homeowners dont get to return parts to supply houses without a restocking fee thats high enough to make you wonder...

As a rule, those boards dont fail that often....those Armstrong units are bad about water in the vac lines however...they are also real touchy about the draft proving switch that if you didnt use an EXTREMELY small vac on the switch, you toasted it since it isnt designed to survive being sucked on....that might be part of the problem...particularly if that unit has the black plastic one(s) on it....and they are realy bad about loosing ground to the module.... Best advice....get someone out that can troubleshoot it correctly...and knows that knocking on parts in a unit is not the right way to fix them.

[Anthony Diodati]

********I take it you are a HVAC man, so NO, i would not try to tell you "See, I was right, I'm a cable installer, and I know more than you,"********** **********because I see what your saying, Maybe I but a new board, and fix the ground at the same time.*********

As a rule, those boards dont fail that often....those Armstrong units are

that if you didnt use an EXTREMELY small vac on the

**********Actually I let the combustion fan draft, I believe it is the right term, supply the vacuum***************** ********Do you mean a plastic vacuum diaphram? This one is metal, ************* ....and they are realy bad about loosing ground to

***********Is one of the 2 wires on the switch a ground, or is it grounded to the metal of the furnace? I did see a ground wire on the ignition control, and had thought about checking that.******* what if

valve,IOW a bad "whatever"?

I understand what you are saying but please understand it was 9:00-9:30 at night and I was just trying to get heat, I did not beat the shit out of the board, but rather tap'd it lightly. Thank You, Tony D.

[Anthony Diodati]

CBHVAC, I have no doubt that you are a competent repairman.

Hovever I remember last winter when I asked about the last problem in this group, with the inductor fan,(Title, Ultra II 97 furnace won't light, )

After I told you we were stuck in a blizzard,and snowed in, and all the detail I had given about how I reached my conclusion that the fan was bad, and was there somthing else I should be checking, You gave me some Smart Ass Crap about "Yea The Yellow Pages for a service company to check it, and fix it." Two other posters told me to replace the inductor fan without all that "yellow pages, and throwing parts at it business. You did go on to say you agreed with "heatman" about the inductor fan, but I

*COULD* have other problems and if the inductor fan was indeed bad, (BTY witch it was, I later confirmed voltage to it, and also supplied voltage to it(off the Unit)"bench test"so to speak") That it may have taken out the board. Weather or not it did, or possibbly took a toll on it at this time I don't know. It very well could have just a bad ground. That "throwing parts at it" seems to be your catch phrase. Like I said, I needed heat for me and my wife last year in the snow storm, and needed heat tonight, so I did what I had to do. I'll also tell you that I worked as an auto mechanic for many years, and often times taping on a compantant would get the car to start,in the case on an ingition module, or for the engine to falter, in the case of a bad mass Air Flow sensor on a GM car. That is Why I did it. That and the fact that I needed heat in the middle of winter. Thank You for your time.