No gas to cook top

Hi enhas,

I'm sure I'm going to learn something from your post, but I'll offer what have come to learn on your topic.

Many/most stoves that are part of a low pressure (11" WC) LP gas "system", (system meaning there are other appliances running on the same gas line feeding the stove,) use a stove mounted gas regulator. The stove regulator takes the incoming 11" WC gas pressure and steps it down to 10" WC. This step down regulator helps the stove burn more even when other appliances on the same gas line operate.

For example, you are cooking at 10" WC pressure on a stove top burner. You have the burner control knob (an adjustable orifice) set to the heat you want to cook at. Then, the furnace or water heater starts up. That large LP draw makes the main tank regulator droop and then open up. A slight dip and then a spike in the LP pressure can occur when the other appliance starts and the main system pressure may go slightly down and up from 11" WC to 12" WC or slightly more, until the main tank regulator has time to adjust. And some RV main regulators will not hold a constant 11" WC, they may drift up and stay up. They should not go higher then 14" WC. With all this gas pressure moving around, your stove top burner stays "closer" to the same as the stove regulator when it works right as it is running at a slightly lower pressure to help with the dip, and it helps tune out the spikes. Thus you do not burn up your meal.

I tried to find some info on your Dometic D21 cook top. Here is the manual I found https://www.manualslib.com/manual/1794703/Dometic-D21.html?page=7#manual Page 7 shows and states you are hooking up to a stove regulator. Not an excess flow device.

Here is a D21 for sale, and scroll through the pics to see the Seven Universe R60 stove regulator. That same R60 regulator is also used as a replacement part in the older Atwood stoves https://reparadise.co/great-products-for-your-camper-rv-and-van-conversions/appliances/dometic-d21-cooktop/

I tried to download the install manual off the Dometic site, but I keep getting a 404 error, their link must be broke. https://www.dometic.com/en-us/outdoor/food-and-beverage/mobile-cooking/rv-and-boat-cooktops/dometic-drop-in-cooktop-138696


Unless Dometic changed something with the model you have, the D21 is shown to have a stove regulator to drop the 11"WC down to 10" WC.

Something is not adding up with this response from Dometic that they told you. This one, http://forums.trailerlife.com/index.cfm/fuseaction/thread/tid/30325772/gotomsg/30326155.cfm#30326155

They never defined what "high elevation" was. 10,000 ft is often referred to as high in many instances and the air is thin that high which might mess with the LP/air mixture, but you would think the LP gas would light, but the flame be all yellow.

Searching around the web, this Dometic issue shows up, not only on your model.

A few I found
https://www.rvforum.net/threads/operating-on-propane-at-high-elevation.87986/

This one had a poster state Dometic told them 4,500 ft was the limit, yet that does not show up in the install instructions.
https://www.forestriverforums.com/forums/f224/dometic-cooktop-won-t-operate-above-4500-a-218875.html

I am not sure what the real issue is, I have had issues with that same R60 Seven Universe regulator before not regulating down to 10" WC on the Atwood range tops. In my case, it would not regulate at all. It passed what ever tank pressure was coming down the line. After 6 new regulators and 4 very upsetting calls to Dometic, I gave up on them and their tank regulators. I am at 500 ft elevation.

This sort of points to the stove regulator not working right for a reason I would really like to learn why. Suburban uses a different brand stove regulator and that may be why others have their stoves work in the range your kids camper is at, but yours does not. The Seven Universe regulator may be the issue.

Hope this helps and please report back.

John

Finally was able to speak with a propane valve engineer. He surmises that what I havre taken for a regulator at the cook top is actually a flow shut off valve installed there for safety reasons. As he explains it, this is not mandatory but is sometimes used to shut off flow in the event of a line rupture. On the cook top at high elevation, when the stove valve is opened, the atmospheric pressure is not sufficient to push the ball/spring arrangement open against the flow supplied by the main tank regulator — which I believe is a constant at a given regulator setting. The flow control valve senses too much flow and closes, shutting off the gas entirely. He says that the flow valve is only there for safety reasons. Soooo, I am wondering if turning down the main regulator at the tank is a solution.

OK, reviewing some of my physics, I see the source of my error. Spring tension in a regulator is a constant function of the length of the spring. It is not assisted or detracted by atmospheric pressure. Thus, the pressure on the diaphragm of the regulator is a constant at a constant spring length.

You may be right about debris. We'll see. But here's where I get lost. The regulator is set by the spring pressure and the ambient atmospheric pressure. More pressure on the spring pushes down on the valve and opens it making for more gas flow output and more pressure. But when the spring is set in the first place it is done in conjunction with ambient atmospheric pressure on the diaphragm. At higher elevation, that atmospheric pressure is less and the valve moves a tad toward closed — like turning the spring screw a bit counter clockwise (which will also decrease output pressure). The regulator itself is not closed to the atmosphere, though the tank is. What am I missing? I do grasp that the oxygen changes and that influences the flame efficiency. Urged kids to tap the stove regulator. Don't know if they did. We will work on this in the week ahead, but it is difficult/impossible to diagnose an altitude issue at now a lower elevation!

Enahs,

Before you get too much farther, inspect the unit and locate the regulator part. Then, with the gas on and a burner on, give it just a light tap with just about anything that is not hard. A plastic screwdriver handle will suffice. The regulator may just be stuck closed. It happens more often to new than used.

Matt

A little clarification on pressure readings. When pressure is measured it is normally gauge pressure. That means that it is the difference between atmospheric and supplied pressure. The regulator supplies a set pressure above atmospheric pressure. As atmospheric pressure changes the absolute pressure changes with it but the gauge pressure doesn't.

It isn't the gas pressure that changes with altitude but the amount of Oxygen in the air that changes which causes a rich mixture. The change can cause a less efficient burner but it shouldn't be enough change to keep it from working till much higher elevation.

With this being a new camper I suspect that there is some debris in the system that is causing the problem.

Have been talking with Escape. They are interested and willing to be helpful. Dometic has given them the same altitude response. Kids are back to lower elevation and stove is working but the furnace isn't. This will get more discussion on Escape. BTW, it was on the Escape forum that I first discovered the altitude issue with the Dometic D21 cooktop. There has been no final resolution. I resorted to this forum (as I have in the past) because of its larger, diverse brand membership. OTOH, Dometic is widely used. Meanwhile, I've managed to learn exactly how a regulator works, and it is clear that a number of things can affect it. Some "experts" insist that altitude can affect the air/fuell mixture and thus the efficiency of the flame but it does not affect the regulator itself. Others say it can affect the regulator diaphragm since the regulator is not closed to the atmosphere. But clearly atmospheric pressure does affect something more than the flame quality. In this case (and others), there was no gas flow at all, suggesting the regulator had closed due to insufficient pressure on the primary or secondary sides or both.

I frequent the Escape Forums and actually do not recall a Dometic stove top mentioned. The Suburban gets lots of mention however.

LOTS of gas devices use a second regulator. My propane powered Onan generator has a very large diaphragm regulator in the housing, but gets its gas from the regulator at the cylinders. Stoves do too.

I carry a portable butane single burner and a electric hot plate with me to cover all possibilities.

I think your question is worthy of some discussion on the Escape forum as you have a lot of people with the same equipment on there.

Charles

Now things have suddenly gotten a bit cloudy. For a week the only issue has been the stove — no gas at all, which made me suspect the regulator at the stove not opening. Now, last night, for the first time the furnace would not stay lit. Beginning to suspect the main regulator at the tank (or both regulators). All this stuff is brand new. Very frustrating.

I camp at 4500 to 5500 all the time and have never had an issue except once. it was when the main regulater was starting to go bad so it wasnt providing enough pressure to the stove when something else like the fridge was running. the stove did light but it looked bad, thin yellow flames and such. this might not be your issue but worth talking a look at it while your at it.

Steve