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Old 03-06-2011, 09:16 PM   #1
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Converting Robertshaw Gas Valve 7100 DER-S7C


Hello,
The following took several days and much more time than I wanted for the 45min actual conversion. I hope this will help others:

Furnace = Lennox Whisper Heat = G20 Series Q3-4E-100-1 (100,000 BTU)

Ignition Control = Robertshaw SP735L / (Lennox 18G9101 obsolete) = now Robertshaw/Honeywell SP735L

Gas Valve = Robertshaw (7100 DER-S7C 1/2in - 1/2out obsolete) = now Robershaw 720 Series = 7200 IPER-S7C 1/2in - 3/4out. FYI: If Robertshaw 720-070 UNI Kit is ordered it INCLUDES a 3/4 to 1/2 bushing + LP conversion kit + new pilot tube connection on valve side.

Notes: This valve looks nothing like the 7100. Which is good. From what I've read and observed the 7100 is junk! The primary started sticking and got to a point where the main was stuck open. So every primary ignition (when the primary decided to open) included the main burners before I caught up with the problem.

The 7200 with the bushing installed is still about 1" shorter than the old valve. You will have to have a new pipe threaded or go flex to make up for the difference. My union was installed high enough for me to still use the old pipe although I'm sure it was at the end of the tolerance that would make most techs comfortable. I shot it with suds and all was good.

The 7100 has a double male single female - piggy back on P (Orange). On the new 7200 the terminals are all recessed. So you will have to obtain a double male single female (DMSFN-250-100.) Dig in your electrical drawer. These buggers are 10$ ea before shipping.

The 7200 comes with the regulator factory adjusted for natural gas. Don't play with it. If you do the LP conversion the regulator should be adjusted for 11" W.C. A manometer or pressure gauge set was out of my budget (free.) Google water manometer and this can be set up for less that 10$ I personally wouldn't make another. I could barely tell the difference by looking at the flame unless I was at either end of the spectrum on the adjustment screw. I'd put it in the middle and call it good so long as my flame was blue with very little yellow. But that's me. Pro's feel free to chime in on the ramifications of this setting not being exactly 11" W.C.

It all sounds scary to the average DIYer. But I had the whole thing done in about 45min. I had to cycle the valve about 5 times to get the pilot to light. It hasn't had a problem since. Keep in mind the S7C means slow opener. It takes a few seconds for the pilot to ignite. Obviously it was lighting in milliseconds with the main stuck open. Not KOOL.

I can't stress testing with some dish soap suds enough. Make double sure your not getting any bubbles on the input side before you fire the new valve. And on the output side and pilot connections afterward. Especially if your going to reuse your pilot tube. The new valve includes the valve connection for the pilot tube. But I didn't have new compression fitting to support the rest.

Good luck. Hope this helps, Mike
New 7200 on left - old 7100 on right
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Old 03-06-2011, 10:48 PM   #2
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Converting Robertshaw Gas Valve 7100 DER-S7C


Me I tend to only install honeywell gas valves, they have a nice conversion chart to tell you if your coming from Robertshaw or anything else.

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Old 03-06-2011, 11:20 PM   #3
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Converting Robertshaw Gas Valve 7100 DER-S7C


Forgot to mention. Any references to the ign. Controller all lead back to the same part wether it be Robertshaw or Honeywell. Most say Robertshaw/Honeywell in the reference. Made me think they were the same. Per my other thread on the 7200 - I had enough run around and just called Robershaw directly. Sales had me at wits end. Looking back now I would have checked with HW first. Hard enough to keep up on the electrical side. HVAC = I'm lost on who owns who. But I will say in the hrs of reading that I did that Honeywell was the best talked about by all the mods as well as the subs. I just wanted a darn valve....

Last edited by mikefrommi; 03-06-2011 at 11:36 PM.
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Old 03-07-2011, 05:36 AM   #4
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Converting Robertshaw Gas Valve 7100 DER-S7C


Get that furnace looked at by a PRO to ensure the Heat exchanger is not cracked!
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Old 03-07-2011, 07:41 AM   #5
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Converting Robertshaw Gas Valve 7100 DER-S7C


Good idea. We have a 5' lighted video scope at work. I'll bring it home and run it up inside to check. I did brush and vacuum it all out - as well as the burners when I did the valve. I didn't see anything from the front. The scope can feed right up inside. Is there a place where the cracking usually occurs? I'd assume above the flame of each burner where the heat is at it's highest.... Thanks for your input.
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Old 03-07-2011, 12:19 PM   #6
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Converting Robertshaw Gas Valve 7100 DER-S7C


Typical crack location on that furnace is on the back where it first narrows. It will look like a 1-2" rust line next to the seam.
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Old 03-07-2011, 05:50 PM   #7
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Converting Robertshaw Gas Valve 7100 DER-S7C


again, have a PRO check it even if you don't see it, because you are not attuned to know exactly what you are looking for.
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Old 03-07-2011, 06:06 PM   #8
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Converting Robertshaw Gas Valve 7100 DER-S7C


Quote:
Originally Posted by mikefrommi View Post
Hello,
The following took several days and much more time than I wanted for the 45min actual conversion. I hope this will help others:

Furnace = Lennox Whisper Heat = G20 Series Q3-4E-100-1 (100,000 BTU)

Ignition Control = Robertshaw SP735L / (Lennox 18G9101 obsolete) = now Robertshaw/Honeywell SP735L

Gas Valve = Robertshaw (7100 DER-S7C 1/2in - 1/2out obsolete) = now Robershaw 720 Series = 7200 IPER-S7C 1/2in - 3/4out. FYI: If Robertshaw 720-070 UNI Kit is ordered it INCLUDES a 3/4 to 1/2 bushing + LP conversion kit + new pilot tube connection on valve side.

Notes: This valve looks nothing like the 7100. Which is good. From what I've read and observed the 7100 is junk! The primary started sticking and got to a point where the main was stuck open. So every primary ignition (when the primary decided to open) included the main burners before I caught up with the problem.

The 7200 with the bushing installed is still about 1" shorter than the old valve. You will have to have a new pipe threaded or go flex to make up for the difference. My union was installed high enough for me to still use the old pipe although I'm sure it was at the end of the tolerance that would make most techs comfortable. I shot it with suds and all was good.

The 7100 has a double male single female - piggy back on P (Orange). On the new 7200 the terminals are all recessed. So you will have to obtain a double male single female (DMSFN-250-100.) Dig in your electrical drawer. These buggers are 10$ ea before shipping.

The 7200 comes with the regulator factory adjusted for natural gas. Don't play with it. If you do the LP conversion the regulator should be adjusted for 11" W.C. A manometer or pressure gauge set was out of my budget (free.) Google water manometer and this can be set up for less that 10$ I personally wouldn't make another. I could barely tell the difference by looking at the flame unless I was at either end of the spectrum on the adjustment screw. I'd put it in the middle and call it good so long as my flame was blue with very little yellow. But that's me. Pro's feel free to chime in on the ramifications of this setting not being exactly 11" W.C.

It all sounds scary to the average DIYer. But I had the whole thing done in about 45min. I had to cycle the valve about 5 times to get the pilot to light. It hasn't had a problem since. Keep in mind the S7C means slow opener. It takes a few seconds for the pilot to ignite. Obviously it was lighting in milliseconds with the main stuck open. Not KOOL.

I can't stress testing with some dish soap suds enough. Make double sure your not getting any bubbles on the input side before you fire the new valve. And on the output side and pilot connections afterward. Especially if your going to reuse your pilot tube. The new valve includes the valve connection for the pilot tube. But I didn't have new compression fitting to support the rest.

Good luck. Hope this helps, Mike
New 7200 on left - old 7100 on right
Congratulations.
You are the only living human to take a simple gas valve and make it sound as complicated as the science that went into the
Manhattan project
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Old 03-08-2011, 12:40 PM   #9
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Converting Robertshaw Gas Valve 7100 DER-S7C


Quote:
Originally Posted by hvaclover View Post
Congratulations.
You are the only living human to take a simple gas valve and make it sound as complicated as the science that went into the
Manhattan project
Complicated???? Maybe to you To a DIYer - It's everything they need to know to do the job and not make additional purchases. Nothing more - nothing less! Let's not misinterpret informational and complicated. If I had posted this in the Pro forum - I could see where your coming from. But over here you sound like a Pro who's getting money taken out of their pocket. And I noticed you also didn't answer my reply as to where the cracks show up. I do these post on the electrical side all the time and get praise from the mods. Then again, usually when a person has as many posts as you....well we all know what that means! Or you'd be a MOD. Thanks for your "help"

Thanks Marty!

Last edited by mikefrommi; 03-08-2011 at 12:48 PM.
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Old 03-08-2011, 12:46 PM   #10
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Converting Robertshaw Gas Valve 7100 DER-S7C


Quote:
Originally Posted by hvactech126 View Post
again, have a PRO check it even if you don't see it, because you are not attuned to know exactly what you are looking for.
Hey, I stopped by a local shop and the fella was nice enough to bring me in back and show me what to look for. In return I'm going to record when I go through mine with the scope and put it on a DVD for him to use as an aid for his techs.

I'll admit I took this fairly lightly until he showed me a bad unit. Thanks for your input. I wouldn't have stopped if you hadn't posted this.

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