Furnace gas valve

BFL13 wrote:
Here are three photos of what goes in an 8531-II or III. It appears the gas valve is part of this assembly. 25M16V Type 701 is marked on it as shown.

Yeah…that’s exactly what mine looks like. I’m actually rebuilding my camper from scratch so I have some freedom to adjust my gas line however I need it. I just need a valve that will bolt up to my furnace and allow it to run.

By the way, I’ve heard the actual burners are obsolete as well. I see you’ve gone through a couple. Where do you get replacements? I don’t need one now, but I might buy a couple to have on hand just in case.

I think that 31150 would work. Just screw in your own inlet and outlet parts to the "back" and "front" holes (where those red things are?)


The burners are on Amazon. They now have a metal cover over the orifice then the screen starts. Works the same.

The sparker set they sell now has bent probes instead of straight like OEM. I was able to get separation above the screen by using washers as shims to tilt it up a bit. Hard to explain. I have a photo of that somewhere: OEM straight set seen there too. The straight ones were too far above the new burner screen and the new bent set was touching the screen, but is ok shimmed up as seen there.

Bob E. wrote:

For the 31150, the gas outlet is in the wrong place. In your 2nd photo, the gas outlet is on the far side. On the 31155, the gas outlet would be to the right where your finger tips are, which is how mine is. Once mine is mounted in the furnace, the solenoids sit upright and the gas flows straight through from back to front. I suppose I might be able to rotate a 31150 and mount it sideways and use some fittings to get the gas line to the inlet port, which would face down, which is how it looks like yours is mounted. But I don’t have that L-shaped tube between the valve and the burner that is shown in your last photo.

Do you know if those caps with the allen head screws are removable? If so, could I swap the outlet from the side to the front?

Hi Bob,

It seems there are different versions with the -II rev. I'll add some more pics of the 31150 so you can see if you can make it work. I looked in the 2003, 2007 and 2015 service manual and the -II rev 8500 series furnace called out a different valve part number in each manual. It seems they kept changing suppliers or valves etc along the way. I know the coils are slightly different on the wire connections on the new 31150 verses they old valve (2003 vintage) I replaced, but that did not stop the new valve from working.

The 31150 is made as a 90 degree valve. There is a pipe plug on the non outlet side opposite the actual outlet port, smaller NPT size but there is one. The 31150 had no outlet straight through from the inlet port like is seems you need.

I will have 2 of the 31150's arriving this week. I can take more pics or measure if that helps any.

See here for some more pics I have from earlier this year.

The inlet is on the right in this pic. See the molded in flow arrow.


The opposite side plugged outlet, smaller NPT port


There is no port on opposite end of the inlet port on the 31150


Here is the gas valve installed on the bench in 2010 in these 2 pics. These pics are of a 2003 vintage gas valve as that was when the camper was made the pics came from




Also to note, this pic is from 2010 as the date says and that valve is from a 8530-IV from 2003 which "looks" like it might have had a plugged discharge port straight out opposite the inlet. That feature went away with the current day 31150.


And this pic is of a 8520-IV and the valve is from 2003 installed. It too has what might be a port straight out, but again, That feature went away with the current day 31150.



Hope this helps

John

Thanks guys! These photos and information have been very helpful. I ordered the newer gas valve (#31098) because it looks like it has the gas inlet and outlet ports in the correct place (or at least close to it). Supposed to be delivered Thursday. I'll let you know if it works when I get a chance to mess with it...hopefully this weekend. If not, I may have to go with the 31150 and try to find that L-shaped tube on the outlet side. Otherwise, I don't think I will have enough room at the bottom of the valve to connect the gas line on the inlet side.

Bob E. wrote:
Thanks guys! These photos and information have been very helpful. I ordered the newer gas valve (#31098) because it looks like it has the gas inlet and outlet ports in the correct place (or at least close to it). Supposed to be delivered Thursday. I'll let you know if it works when I get a chance to mess with it...hopefully this weekend. If not, I may have to go with the 31150 and try to find that L-shaped tube on the outlet side. Otherwise, I don't think I will have enough room at the bottom of the valve to connect the gas line on the inlet side.

Hey guys just wanted to drop in here and thank everyone for this thread. I have the hydroflame 8531-iii and encountered the exact same problem of not being able to find the Atwood 31155 gas valve because, well, they just don't make them anymore.

So, even though I didn't know the results for Bob, I took the plunge and ordered the Dometic 31908 from Amazon as suggested, and it worked!

BUT... it's never that easy, right? It took several hours of trying different things and head scratching, but eventually I got it to work by installing it sideways with the input port pointing UP (solenoids on the left, touching the fan housing), and drilling a hole in the top sheet metal to bring in the gas line from above. Additionally, I had to move not just the orifice over from the old valve, but the orifice AND the carrier "tube". Mercifully, the threaded outlet port on the 31908 is 3/8" npt thread, just the same as the 31155, so no adapter required. I had to do this to provide enough clearance to plug the ignitor wire in.

Now, if drilling a new hole is absolutely out of the question for you, I think it WOULD be possible to very creatively use brass elbows and pipe nipples to get the input where you can use the existing side entrance setup. My GUESS is you'd probably want a 3/8" female flare to 1/4" female npt elbow, a couple of 1/4" street elbows, a 2" nipple (or maybe 1.5"?), and finally a female 1/4" npt to 3/8" male flare elbow. Alternatively, you might also be able to use a 3/8" flare street (swivel) elbow and a short piece of rubber/flexible propane hose - although with the exhaust pipe running through the same space I wouldn't take that kind of risk. Note that the inlet in this configuration is maybe an inch from the top sheet metal, so if you put an elbow on it will be touching the "ceiling" - not much room!

For me, just cutting the hole in the ceiling made the most sense. It was the least expensive option and I just sort of stuffed some fiberglass insulation around the copper line once the flare nut was poked through. The furnace is very old and I just need it to work. The RV is also old and doesn't move (much), so I'm not worried about rubbing. You might decide to install some sort of grommet if you're going to be moving.

Finally I might also note that there is a stamped bracket on the original valve that helps attach it to the fan housing, giving the whole works a little more rigidity. My furnace no longer has that feature due to the completely different valve and configuration.

Anyway, thanks again, especially to BFL13 who made the suggestion. I have heat now, which is what matters!

EDIT: Here's what it looks like installed...

Just WOW, what a pain! Hope mine holds up before having to do all that.