Need help with an older Payne furnace

jeremys

Hi All,

I have an older gas furnace(house was built in '72, & from appearance alone, I'd be shocked if the furnace has been replaced.) It's a side draft, rooftop model. The name plate has been painted over with silver roof paint (thanks, previous owners) so all I can really see is the brand, Payne. It is a pilot lit model, with the thermocouple as part of the pilot assembly.

The problem it is having is that the burner will not reliably start. When I turn it on, it will go through the normal delay, then the blower comes on, burner never having started. while I was trying to trouble shoot the issue, trying to see voltages across different parts, the burner has cycled on briefly, for possibly 30 seconds max.

The primary suspect with these older models always seems to be the pilot/thermocouple assembly, but I replaced it last year, & I tested the leads for continuity with a hot bimetallic strip, & it's closing.

There are 3 parts in the burner area with wires to them: the pilot, the gas valve, & another, disc shaped part running off a tee in the pilot gas line that my internet searches have failed to identify. I bring this up because twice now, it was when I was either tapping on, or trying to measure voltage across this part that the gas came on to the burner.

Jamie Hall

That flying saucer gizmo off the T looks to me like a pressure regulating diaphragm. Which may be stuck.

Where to get one? @Tim McElwain might know if I'm right, and if so what the fix is.

Tim McElwain

That is a pressure switch which is usually set to the line gas pressure of the system. I doubt you would find one anywhere. Is this a natural gas or Propane systems? If it Nat Gas you could probably bypass that switch which is what would be done if someone had to retrofit this system and install a combination gas control. That however should be done by a professional. Look for a local Carrier dealer as Carrier is also associated with Payne equipment.

Jamie Hall

Thanks, Tim!

jeremys

Tim, would I be able to at least short those wires to confirm I've correctly identified the problem?

Edit: forgot to answer your question, it's Natgas.

Tim McElwain

Yes just make sure the pilot is lit.

jeremys

Roger that, I'll report back on the results.

jeremys

Well, I found the problem with the pressure diaphragm. One of the wires to it was terminated in a ring terminal(an old, thin, pure copper one.) when I started loosening the screw, the ring portion broke off the rest of the terminal almost immediately. Looking at the break, it's obvious that it was hanging on by a tiny sliver of copper, as the rest of the break is oxidized. between replacing that, & a spade terminal at the gas valve that had most of the wire strands broken off at the solder point, the furnace now starts up normally(burner starts before fan) & runs. Thanks for your help so far!

However, now that it has a chance to run, I'm seeing a new problem. After it has been running for ten minutes or so, the burner will cut out for about 5-7 seconds every minute or so.

Thoughts?

Tim McElwain

I would look to replace all the wiring and connections based on what you have already found. Use a multimeter to determine were the power stops (switches or wire connections). Check the secondary of the transformer to see if you have power when the unit stops running. If you do then the problem is in the low voltage wiring.

jeremys

Yea, I was kinda wondering in the back of my head if it might be another wire, especially as the unit shakes quite a bit in operation(I'm going to lug a vacuum up there tomorrow & hit the blower fan on that count.)

Since when it fails, it's properly shutting off gas flow, I'm guessing it's at least safe to run now, would you agree?

Tim McElwain

Yes as long as it comes on and shuts off safely without any delayed ignition or flames coming out the front of the unit.

jeremys

Nope, it's starting exactly like it should. I may leave it off when not home or awake, as the enclosure around the burner area is loose enough that high winds extinguish the pilot, & I didn't test it in a no pilot startup(another thing to try tomorrow.) But at least I made progress, & have a path forward, thanks to your help.

Jamie Hall

Good show. Thanks again, @Tim McElwain !