I Think I Need a New Gas Valve

troodon

Hi,

We have a cabin with an older Williams gravity floor furnace. We bought the cabin this year. The furnace hasn't been used in 20 years, maybe more. The specs are:

Model number: 45FF-H
Serial number: 2541
Equipped for: LP gas
Input: 45,000 BTU HR
Manifold pressure: 10 0 IWC
Min. Gas Supply pressure: 11 IWC
Design complies with ANS1Z21.48 floor furnace: B1988
Date code: 37.90

I can get the pilot to light, and stay lit. It's a millivolt system, so the thermopile is generating enough current to keep the pilot valve open, at least. However, the main gas valve will not turn on. I've tested continuity in the thermostat circuit, and it's good. The thermostat is a 750mv type.

The gas valve, which I photographed in the crawlspace, has a model number VS821A1277. It came up as a Honeywell model when I googled it. Some of the electrical connections look pretty corroded, but there is continuity between them.

I'm not sure if the thermopile is generating enough current to open the gas valve, or if the gas valve even works anymore.

I called Williams to get info about replacing the valve, and a man there said it could be an older "IT" valve, which can't be replaced because the connections are different. I'm not sure what an IT valve is. I also called Robertshaw, and a man there looked up and found the Honeywell model, and said a 710-502 valve with a L.P. conversion would work. I haven't heard back from Honeywell yet, so all I have is a bit of conflicting information between the two people I spoke with.

Here are some photos:







Any suggestions on how I can proceed? Everything I've learned about floor furnaces has been in the last 2 weeks.

EDIT: I do have a great friend there who has experience doing this kind of work, and he'll help out. So I'm not alone in this, but it's up to me to research the answers and get the supplies.

HVACNUT

How is the thermopile generating enough current if the pilot doesn't stay lit? Are you able to measure millivolts and gas pressure?
Aside from that, a 30 year old floor furnace that hasn't been used in 20 years will need a major inspection. Rotted heat exchanger, rusted clogged burner tubes, plugged orifices, etc.
Not trying to scare you but get low level CO  detectors if you don't already have. 

EdTheHeaterMan

I would start with a small jumper wire between TH and TH/PP on the gas valve. (FREE) If that lights the main burner, then there is added resistance in the wiring thru all the limit control(s), thermostat and all the other corroded connections. Remove clean and retighten all the wiring connections.

If that jumper between Th and TH/PP does not open the valve, then I would purchase both the valve and the 750 MV pilot generator. Replace the pilot generator first. (That costs less). If that is not the problem then replace the gas valve.


Make sure the gas valve box is sealed at the supply store. This way if you don't need it, and you don't break the seal on the box, you can return it.

BUT MORE IMPORTANT IS WHAT @HVACNUT SAID!
Get the heat exchanger and vent pipe inspected!

Jamie Hall

@EdTheHeaterMan got ahead of me there -- first thing to do (besides making sure the furnace isn't rusted out -- a good possibility) is to disconnect, clean, and reconnect all the connections that you can. Millivolt systems don't have a lot of electrical oomph, and even one crusty connection can do them in.

unclejohn

And do get that CO detector

troodon

Thank you.

HVACNut: the pilot light does stay lit, provided I hold the key chuck down for 30 seconds or so after lighting it. It then stays lit when the key is in either the "pilot" or "on" positions. I can measure millivolts, but not gas pressure. I measured about 300mv or so, the number jumping around a bit. Here are pictures of the furnace. I can only get these low-res pictures off my wife's iphone, but here they are:






UncleJohn: I do have a normal CO detector, placed in the house in the area above the register. Is that sufficient, or do you mean some special kind that would be placed somewhere else? Sorry for any dumb questions, but like I said it's all new to me.

EdTheHeaterMan: I did try a jumper wire between TH and TH/PP, at the direction of my friend, and it didn't do anything. I like the idea of buying both devices, and trying the thermopile replacement first. I wish I had taken pictures of the venting underneath the house, but it looks pretty good. Shiny galvanized steel, I think. I can take a closer look next time at the connections.

JamieHall: I did that with the connections on the TH/PP screw (loosened them, cleaned them), but I couldn't get enough purchase on either the TH or PP screws to loosen them. There's only 2 inches or so of clearance from the screws to the furnace above it, so I need some special ratchet screw or something. My little stubby screwdriver was no help.

All this would be moot if what the Williams guy said was true -- that this might be an "IT" valve that cannot be replaced. Does anyone know anything about that, or how I might determine whether it's he or the Robertshaw guy who is in the right?

mattmia2

you need a right angle screwdriver or to put an insert bit in a 1/4" socket on a ratchet.

thermopiles wear out over time and gradually produce less current, you probably just need a new thermopile.

It is possible that the valve is stuck though and if that is the case it needs replacement. I think they mean ITT, a company that made a lot of those millivolt valves.

If you replace the valve you will need a tech with combustion analysis equipment to adjust the new valve.

ratio

Is there a limit missing on the HX (the white rectangle in the picture looking down into the unit from above)? Is that a big hole into it with screw holes to either side?

JUGHNE

Your propane gas regulators could be that old and if so, it is time for new ones.

HVACNUT

@troodon, please have a pro recommissision the furnace. @ratio might have saved your life. 

troodon

Ratio: I'm not sure what you mean by a limit missing on the heat exchanger, but yes the white rectangle has two wingnut screws and a window. You can take that off and lower a match into the unit with a long metal rod (also visible in that picture), or use the piezo sparker.

Jughne: You mean the regulator in the main propane line, or one specific to the heater (or maybe even inside the heater)? Apologies for the newb questions... If you mean the main regulator, it's been inspected and the whole line leak-tested by the propane supply company. They tested everything from the tank up to the heater. The heater's the only thing running off the propane tank.

HVACNut: It's not really a typical situation. Very few service people go into this area, even though it's only an hour from the nearest town. It's VERY hard to get anyone (plumber, electrician, whoever...) who's willing to make the drive. I've tried. They have enough more than enough business without going that distance. People up there generally work on their own stuff, and help each other out, and that's my situation. Like I said, I have a good friend who's worked on these heaters before and understands them well, but he's got a full plate. He'll help me with the work, but the research is up to me.

mattmia2: Thanks for the screwdriver suggestion. Yes I think it is ITT. He said it was a company whose valves were found faulty and outlawed. His point was that it probably was that kind of valve, and if so, then all the connections were of a different type and therefore the valve couldn't be replaced, and an entirely new furnace was the only route. But my research shows it's a Honeywell valve. Honeywell got back to me this morning and told me that particular product history is handled by their partner Residio, and that I should contact them.

troodon

Ratio: It occurred to me before that the device in the second picture (the pictures from above), just to the left of the "Williams Furnace Company" label, seemed to be a kind of secondary thermostat. Maybe that is a limit switch?

In the first picture of the gas valve, the two cloth-insulated wires coming down from the unit on the left side of the picture are the same wires that go into and out of that device (limit switch or whatever it is). Those wires come down and one is connected to the TH/PP common, and the other is wire-capped to one of the two main thermostat wires, and returns to the main thermostat.

EdTheHeaterMan

ratio said:

Is there a limit missing on the HX (the white rectangle in the picture looking down into the unit from above)? Is that a big hole into it with screw holes to either side?

That is actually an inspection door with a sight glass opening. You can see if the pilot is lit from that opening. There are wing nuts on either side of the sight glass to remove the cover. With a long metal rod that holds a kitchen match, you can light the pilot from that opening without the need to get into the crawlspace. The cover looks like it is in place and the wing nuts are visible if you enlarge the photo. Can't actually tell if the hole is covered with eisenglass or real glass from that picture.

Still think you should get a professional to check it out before recommissioning. The Gas valve IS a Honeywell and a replacement is still available https://www.supplyhouse.com/Resideo-VS820A1088-Standard-PowerPile-Millivolt-Combination-Gas-Valve-3-4-NPT-x-3-4-NPT. But get a pro to install it. Maybe your propane company has a guy.

ratio

@EdTheHeaterMan, ok, an inspection window makes sense. Since you told me what it is I can see it clearly now.

@troodon, a 'limit switch' is the technical name for a little heat-operated switch that can be used as a high limit to kill the power to the gas valve when something gets too hot, & the inspection window in your picture looks an awful lot like the spot where one should go.

JUGHNE

That location would have put the limit into the flue gases.

There might be a limit stuck to the side of the heat exchanger....maybe.

I think they relied upon the wall T-stat or when you burned your bare feet on the grill.

mattmia2

I think that capillary tube connected to the bellows at the left is the limit.

troodon

Thanks EdTheHeaterMan. I noticed the valve you linked to has a capacity of 335,000 BTU, and my furnace is rated for 45,000. So is it the reducer bushings that would bring the valve's capacity down to fit my furnace's capacity?

Sorry for all the questions, but I really am interested in understanding this stuff. What are the reasons that a Robertshaw 710-502 would not work?

mattmia2

The manifold pressure and the size of the orifices in the manifold set the firing rate. The 335,000 btu is the max amount of flow that can pass through the valve at some sort of standardized condition. This is why it is important to have someone that understands combustion and has the right test equipment set up a new valve.

A particular valve not working has more to do with it physically fitting and lining up with the plumbing. Most millivolt valves would work if you do enough reworking.

Jersey2

If it hasn't been used in 20 years, better make sure the chimney is clear and there's no animal nests inside.

EdTheHeaterMan

45,000 is well within the maximum limit of that gas valve. I see no problem with using it or the Robertshaw valve, as long as the installer is an experienced qualified technician that understands combustion theory and safe practices when it coms to making a fire inside your living room.

If you want to be a DIY when it comes to heating equipment, you can just put some logs on the metal grate that sits on that floor furnace. Add a little lighter fluid and a match. That will get you all the heat you will ever need. After that the house may not be there so you won't need heat anymore.

Do not do this. it is Sarcasm.

Some of your questions leave me to believe that you should get a professional technician to get the furnace in operating condition.

Just Say'in.

Mr. Ed

troodon

Jeez Louise. Forget I asked.

HVACNUT

troodon said:

Jeez Louise. Forget I asked.

You take offense when people are concerned for your safety? That's peculiar. 
This isn't DIY like patching a leaky roof, or clearing the sink trap, or replacing the belt on the washing machine. This is fire. You need a manometer to make sure the manifold pressure is 10" wc. Assuming you'll be converting the valve from natural to LP, you won't know where to set the regulator without it.
Even if all that goes swimmingly, she fires up and you're all toasty and snug. How do you know there's proper combustion and it won't soot up in a week, or a month,  or a year? And a gas appliance can put out deadly CO levels waaay before it starts to soot. 
Nobody here would be cruel enough to tell you it's ok to jump into shark infested waters. With laser beams on their freaking heads. 

EdTheHeaterMan

I had no idea the @troodon was a religious person. Praying to Jeez Louise? Is that the virgin mother of Jeezeus Cripes? Son of Gosh? of the church of Holy Moly?

Let us all pray for his safe return from the supply house. And that he has a long an happy CO free life and is delivered from the fires of Heck after his DIY project.