Hello,
I have a 20 yr old furnace Ducane model # CMPE075U3 . It has been fairly reliable with a couple of glitches such as Exhaust gas blower motor needing replacement, Ignitor replacement 7 yrs ago and a capacitor for the blower. Other than that has been chuggin' along (knock on wood).

Couple of nights ago it seemed to have shutdown ; I woke up in the morning to see the thermostat actual temp at 57 deg. F ; overnight setting was left at 64 deg. F.

Went down in the basement to hear the exhaust gas fan running ; and the the ignitor was on (orange flame) but didn't trigger the pilot nor the burners (thus the blower was not activated).

I turned the power off to the furnace (i.e flicked the power off to the furnace) ; left it alone for a min ; hit power back on and then it all fired up normal ; we got the first floor back to thermostat temp (64 deg. F). Upon reaching set temp ; it shut off the furnace as it should, BUT, never ignited the burners upon falling temp. Once again turning off the power to the furnace for a min ; she lights up, blower works well, we get heat.

I noticed the ignitor / flame sensor (Honeywell part # Q3400A1008 ) didn't seem to pass gas through it's pilot section unless I go through the process of turning the furnace OFF completely (i.e the flick of the switch as I mentioned above). I am "assuming" due to 7 yrs of use in the New England winters that perhaps the ignitor needs replacement, maybe the flame sensor is not getting hot enough??...still can't put a finger on why shutting off for a min then turning on the furnace makes everything come back to normal.

Thank you in advance for your response.

 

I didn't see any replies ; so looked into it some more. The ignitor seems to be fine ; reads 6.1 Ohms ; I have another new ignitor - not being used reads 4.2 Ohms. Not sure if the small difference in resistance would cause intermittent starts.
Also, the manual startups as I do per my above posts are going up which leads me to believe that it could be the Smart valve; I have an old furnace and the valve hasn't been replaced Honeywell part # SV9500H2609 which is long obsolete.
Can someone please let me know if I get an equivalent SV9501 or SV9502 etc would be okay?? I checked online and they look similar with the same connections. What should I watch out for.
Thanks in advance for your response.

 

Welcome to the forums.

My information shows that furnace has a fault LED on the control board in the blower section. Usually that means there is a sight glass in the blower door where you can look in to see the light.

 

Hello, PJ Max:
Thank you for your reply. I could not find any lights in the lower most compartment where the blower is located. See below all pictures including the board.

I suspect it's the smartvalve as it works when I wiggle the wires on both the ignitor and main. It used to start by just flicking the main switch on and off ; and now I have to sort of wiggle the wires

 

Hello,
From the troubles I have experienced with my furnace, it looks to be the smartvalve. Please help me out determine the fitting on the outlet side going to the burners

See pictures of inlet & outlet ports on the Honeywell smart valve SV9500 H2609.

The inlet port is 1/2" NPT connected to a pipe nipple - no problem

The outlet port has a small locknut type fitting going to the burners. I haven't seen this before and was wondering how you deal with it (unscrew and re-screw back into the new equivalent smart valve or what ??).

 

Interesting. I've never seen an electrical fitting locknut on a gas line before. Usually you need to pull the burner out to be able to unscrew the valve off of it. Typically with pipe fittings...... since they are tapered..... they never become tight in the position you want them in. I'm guessing that's the reason for the locknut. Be sure to use joint compound on the fittings.

 

PJMax....thanks for your response.
This is the way it was built from the factory...i.e new Ducane unit installed 20 yrs ago in a new home installation.
I'm wondering if it will be easy to take off??...it does have pipe dope on it and if I damage the conduit style fitting, would I be able to replace it??

Here's what I'm thinking:
> After shutting the main gas valve off, I'll undo the union, then hold the existing Honeywell valve on the back end via a pipe wrench, and use another pipe wrench to undo the 1/2" nipple (& back pipes) ; the Honeywell valve will then just be connected to the outlet port.
> I'll switch the pipe wrench to the burner pipe keeping it still and rotate the Honeywell valve via CCW I believe to remove the Honeywell valve - you think that'll separate it from the conduit & pipe port of the Honeywell valve on the outlet side ??

Thanks in advance for your response.

 

My furnace finally stopped working. The smart valve gets 26.9VAC at the connector but only puts out 0.5VAC at the ignitor port and so won't light the ignitor, and the valve no longer clicks - I cannot get it to work intermittently as before.
I got a new Honeywell smart valve and was all excited to install it in and ran into a few glitches. PLEASE HELP me get the OLD smart valve out. Here is my dilemna:

I can get the union disconnected (& I have), and can remove the inlet 1/2" nipple to the smart valve. However to remove the outlet side connected to the burner, I have got to either remove the burner OR remove the back panel on the back side of the smart valve, because if I only turned the smart valve CCW holding on to the burner tube via a pipe wrench (..after having removed the inlet 1/2" pipe nipple of course), there isn't enough clearance for the smart valve to turn all the way over (...i.e the center line distance of inlet/outlet pipe(s) from the back side of the smart valve to the back panel is 2.5" and from the front side of the to the back panel off the same center line is 3.5"...thus have to make up 1"). I think removing the back panel (which is probably where the heat exchanger is) appears to be like 5/8" should allow it to turn depending on what's behind the panel.

Removing the burner isn't as easy as some others, which are held by a C bracket and 2 screws....I'm not so lucky with my furnace. It seems like I have to remove (2) 5/16" screws that hold the burner bracket to the back side panel of the furnace. Note the burner tube is welded on to a bracket that mounts all the way to the back side panel. It appears that there are 2 dowel pins on the back panel the brackets hangs on to and bolted down via a small mounting plate on to the back panel. Has anyone seen such an arrangement??

WHAT should I do, remove the back plate or remove the holding screws for the burner & not knowing what the dowel pins are attached to??

THANKS IN ADVANCE FOR YOUR RESPONSE.

 

I don't see/work on many of these furnaces. I couldn't find any type of helpful manual either. The burner should be removable solely from the front.

 

PJmax....thanks for your response.

I want to remove just the smart valve...it doesn't matter if I can go about another way. What do you think if I remove the back panel as shown in picture 1.

Also, I can't figure out the removal of the burner from from the front as you say....the mounting screws on the back will potentially remove the mounting plate and looks to have 2 dowel pins...I don't mind going this route but am unsure which is why I posted the message with pictures.

Thanks in advance for your response.

 

You mean remove the panel so that you can spin the valve off ?
That should be ok.

 

Pjmax...thanks for your response....so I'll remove the back panel as called out below in the picture below and hope to spin off the smart valve.
I believe I'll need a new gasket so should I use Permatex (make your own gasket ?) or something else ??
Thanks in advance for your response.

 

The gas train will have to be disassembled to the valve. Then the burner manifold taken out with the valve still attached. Then the valve can be removed.
The heat exchanger panel shouldn’t be removed.

 

Roughneck, thanks for your response....if you scroll below, you'll see my dilemna in removing the burner. This is not a simple case where the burner is held by 2 screws and a C clamp bracket in the front that comes off in a flash. Please see below and I'll gladly remove the burner ; it is not easy as it would seem in the Ducane furnace that I have.
Thanks in advance for your help.

 

I believe the plate comes off in that model. You’ll need magnetized bits for this.

 

roughneck...thanks again, but with your one line response, I'm not clear...
Magnetic bits are EASY...which plate are you talking about??

(A) Are you talking about the back two screws that I remove to get the small mounting plate ?? what about the dowel pins I mentioned??

OR

(B) Are you indicating taking off the back plate near the smart valve so that I get more room to spin the smart valve without removing the burner??

 

The plate holding in the manifold.

 

Hello, All:

I was able to get the Honeywell valve changed via a gas plumber to part # SV9500H2609 to a new valve # SV9502H2522....I am now getting voltage of 26.9V where the blue wires connect to the ignitor ; however the ignitor # Q3400A1008 is not igniting. I had another ignitor put in (I had a newer one also part # Q3400A1008 ) and the ignitor is still not coming on. The old valve # SV9500H2609 only had 0.48V coming out of the ignitor contacts (at the valve where the blue wires go)...so we made progress with new valve which puts out a solid 26.9VAC....but it's still not working.

I looked at the brochure on the new Honeywell valve part # SV9502H2522 where it says to use a Q3450 or Q3480 ignitor. Should I get a new ignitor ?? Q3450 or Q3480 ??

Any thoughts??..please let me know ; my wife is all B.S as I spent $ 500 + and it's still not working.

Thanks in advance for your response.

 

Here's the latest...

As indicated in my last post, the ignitor contacts on the new Honeywell valve SV9502H2522 are 24VAC...I noticed the following on the main 4 pin connector leading into the Honeywell valve.

Out of the 4 ports on bottom left is common bottom right is +24 hot ; I am getting a solid 26.8VAC so that's all good....however between the common and top left is getting on 1.8VAC...should be 24VAC or higher I believe....that's what the manual says.

I went back to the incoming wire on to the first pressure switch - the one that has tube from the exhaust gas fan (the other switches are all in series as you know)...I read the same 1.8VAC. I checked the ohms on all pressure switches they were next to 0.0001 or something ; I touched the pressure switch leads to one of it's terminal and ground chassis and they all read around 1.8VAC.

Do you think I have a bad board??...why isn't the ignitor firing when it has a solid 26.8VAC ?? ; is the Honeywell valve not putting out current ??

PLEASE HELP !! I'm sure there are experts here, but so far I'm batting solo.

Thanks in advance for your response.

 

You checked and found 24vAC on the two igniter wires when the igniter should have been glowing.
Was the igniter plugged in ? It needs to be connected when checking the voltage.

 

Hi, PJMax:
Thanks for your response.
Upon plugging the ignitor into the smart valve, I did not get the ignitor to glow, which is why I took off the connector and checked the voltage on the new Honeywell smart valve, it was 26.8VAC where the two blue wires go, and upon plugging the ignitor connector back on, it wasn't glowing.
The board is providing 1.8VAC to the first pressure switch...please read my previous post..maybe the ignitor relay is not firing??...as indicated in my previous post the common & pressure switches/thermostat connector should be getting 24VAC ; it is only getting 1.8VAC.

 

The picture shows the wiring.
The bottom two terminals are always live 24vAC.
EFT runs the fan timer.
24vAC on the t'stat/pressure switch terminal starts the burner.

It appears you don't have that last 24v. I don't have any schematic or wiring diagram for your furnace but you need to follow the circuit back to where the 24v originates. If the 24v originates on the control board then it could be a control board or connector issue.

 

I have success but not out of the woods yet. See attached picture, the burners are lit.

I went across each switch and was surprised to see 27V on the flame rollout switch on one side of the voltmeter prong (touching the other to the frame) ; the opposite side of the rollout switch was reading 1.8V ; I did a continuity check and it read zero ohms...darn...and then I remembered that the flame rollout switch had a small reset button on the bottom ; I pushed it and in a few seconds the gas came out ; the ignitor lit and the flame came on, burners lit ; the blower started etc...BUT, I had to shut the furnace...

The pilot flame is too strong; I tried adjusting by taking the small screw off and went clockwise on the adjustment screw until I had it all the way bottomed out and didn't make any difference. Is there an orifice that's missing from the smart valve's pilot tubing side??

 

In the picture we are looking at three gas burner tubes. The left one looks very bright. Are you telling me that's from the pilot light ??!!?!? That looks more like a problem with the burner orifice.

The pilot light assembly would have an orifice directly below the pilot flame, igniter and flame sense rod.

 

The picture on the left yes....but it's not very clear ; but it is the pilot flame that is strong causing it to look like that....the pilot flame even when it first glows is hitting all the way to the end...how do I slow it down ??

The picture on the left should look like the other two burners on the middle & right, but they are not because of the pilot flame...I'm thinking there needs to be an orifice that goes on the pilot line tube that the installer failed to put in. I did find such an orifice in the old valve.

 

I've only seen orifices installed at the flame area.

 

Pjmax...please try to understand....the pilot flame when it comes on is too strong..i.e even before the burners light...the pilot flame is like 3" long where as it should be 3/4" long if you know what I mean...the burners fire fine but the pilot flame is too long. The pilot adjustment didn't do anything so I'm thinking the orifice got left off.

 

I do understand what you are saying but the pilot orifice is usually right below the flame where the gas and air mix.

 

I'm all set with my furnace (keepin' fingers crossed) ; I had the heat guy come back again as he had changed the smartvalve but failed to install the orifice ; upon installing the orifice the flame is right and the furnace is back up.

3 to 4 weeks of dancin' around for nothing...hopefully my post helps others. While I appreciate people that answered my post,...in my humble opinion, being an engineer, I was able to diagnose it all, practically myself with little help from others. There are many wrench turners around, but not people who understand technical aspect of things.

I'll try and help anyone that I can with their troubles.