water heater works fine - IF- I leave door open

There IS NO adjustment on this Suburban. Just make sure the burner tube is clean. A LONG shot for this problem could be the Burner flue tube has a Insect nest. The standard test for this is to roll a golf ball from the top exit and it should come out at the burner. Doug

Timeking wrote:
Wow. Learned something new, surprising at my age (72) and the fact I am a degreed chemist with 37 years experience in environmental science. Just when you think you know it all ... you don't!!!

There is nothing in the Suburban manual that suggests the air/gas mix can be altered, and it doesn't look like it is possible.

Air adjustment may not be very obvious but there should be an adjustable "shutter" near the gas valve and orifice on the burner side.

Found a video that should be helpful on finding and adjusting the shutter..

HERE

Of course, if your water heater has worked fine in the past with the door closed, something else may have changed to cause your current issue and I would be concerned that it has changed.

Typically a clogged orifice from dirt or spiders causes the most trouble with propane side of things so make sure you have cleaned the orifice and burner before making any air adjustments.

You are looking for a good all blue flame, any yellow color is incomplete burn which is typically improper air/fuel mix. But keep in mind the mix changes slightly when the door is closed.

What is the exact model of the water heater? Tag should be on frame of the unit.

Wow. Learned something new, surprising at my age (72) and the fact I am a degreed chemist with 37 years experience in environmental science. Just when you think you know it all ... you don't!!!

There is nothing in the Suburban manual that suggests the air/gas mix can be altered, and it doesn't look like it is possible.

Timeking wrote:
"The RETURN millivolt signal for flame is NOT that strong and will be disrupted by a slight short to ground." Return signal? Are you saying that the Suburban design uses the spark apparatus as double duty for whether or not the flame lit? If true, that seems dumb.

There does not appear to be any damage to the orange wire, looks new. The connection to the lug is shiny and clean.

As suggested, I cleaned the burner tube. The air-gas mixture is fixed, not adjustable.

--- Are you positive the air mixture is not adjustable? On all RV WHs I've seen, there is a mixture adjustment where the burner tube meets the gas valve. You adjust it by loosening a small screw and twisting it on the tube to open or close the slots in it to add or block air.

smthbros wrote:

Old-Biscuit wrote:

Timeking wrote:
"The RETURN millivolt signal for flame is NOT that strong and will be disrupted by a slight short to ground." Return signal? Are you saying that the Suburban design uses the spark apparatus as double duty for whether or not the flame lit? If true, that seems dumb.

There does not appear to be any damage to the orange wire, looks new. The connection to the lug is shiny and clean.

As suggested, I cleaned the burner tube. The air-gas mixture is fixed, not adjustable.

Not only does Suburban but also Atwood/Dometic, Norcold for water heaters, fridges, furnaces etc

And it is VERY Smart technology
When the Flame ignites ti creates a current (Flame Rectification)
Flame generated AC Current is rectified into a DC Current which the circuit board senses via the milliamp signal thru the Spark Electrode.
All this takes place w/o further devices/equipment/sensors and happens within seconds of gas valve opening/spark electrode firing
No flame proving signal....circuit board shuts down DC to gas valve---hence no excess raw fuel

My understanding is that the flame conducts electricity between the flame sensor and burner. In doing so the current is changed from AC to modified DC, hence the term rectification. However, since the supplied electricity to the heater in an RV is already DC, how can there be rectification?

Read FLAME SENSING BASICS

"Flame sensing rods, also known as flame rectifier rods or flame rectification rods are commonplace in modern hot surface and ISI (intermittent spark ignition) gas-fired appliances.

Flame sensing rods stick out into the flame and connect back to the furnace board. Once the board sends a call to the gas valve to open, it monitors the current flow on the flame sensing rod. It does this by generating a potential (voltage) at the flame sensing terminal, this terminal is connected to the sensor with a conductor. When no flame is present there will be potential at the rod and no current, when a flame is present a small microamp (?A) DC current will be present as a path is made between the rod and the ions in the flame. This small DC current signals the board that flame exists and all is well with the world. If it does not sense this microamp (?A) DC current within a few seconds it will shut off the gas valve and try again.

The board outputs this potential (voltage) on the flame sensing terminal right at the beginning of the sequence to confirm that the path is “open” with no flame. This ensures against false positives (sensing flame/current when there should be none) and once it goes from 0 current to the rated microamp (?A) current the board “knows” that flame is present.

These flame sensing rods are “dumb” devices. They do not generate potential (volts) or current (amps), their predecessor the thermocouple (seen in standing pilot systems) does generate a potential itself which is often the source of the confusion.

A flame sensing rod is a piece of metal with a ceramic insulator that keeps it from grounding out. That is all. However, because it is conducting in the Millionths of an amp (microamp) a lot can go wrong with it that a normal electrical component wouldn't have any issue with. Tolerances are tight so small factors make a big difference.

Flame sensors fail when:

They short out due to a cracked insulator
They Fail open because they are broken
They don't conduct because they are not properly placed in the flame
They become coated in silica (glass) or carbon"


In a nutshell, the controller board is looking for an "open" (no flame condition) or a small "leakage current" (flame condition) as the exchange of Ions between the flame and rod lower the resistance causing a small amount of leakage current to flow..

The control board places a small voltage on the rod, the flame basically "conducts" a small amount of current between rod and burner.

Conduction will be one direction so it acts like a "diode" or "rectifier" if you will.

HERE is more theory..

"When the gas / air mixture is controlled, the outer blue cone will actually carry electrical current similar to a wire.

If we place a metal probe into this “Ionized Plume” and apply a voltage between it and the burner, current will flow. An important characteristic of a burner/flame/electrode assembly is its ability to mainly pass current in one direction. It behaves as a one way valve or rectifier.

Flame Rectification systems make use of this directional characteristic when detecting a good flame to distinguish it from leakage currents that can arise due to moisture contamination, soiled igniter tip, poorly grounded burner spreader ring / burner head, cracked igniter insulation or poor house ground.

An AC voltage is applied to the electrode from the spark module and the resultant current flow which is greater in one direction than the other, is electronically detected. This current is very small, about one microamp (one millionth of an amp)."

In this case they are talking about a home appliance that is using the same spark gap ignition probe as a flame detector But it still applies to any gas burning device using a flame sensing rod. Using a AC spark voltage they can prove if there is flame or not by monitoring the direction and strength of current flow on the ignition probe.

For much more info on how this works HERE is a Web search for flame rod detection theory..

Old-Biscuit wrote:

Timeking wrote:
"The RETURN millivolt signal for flame is NOT that strong and will be disrupted by a slight short to ground." Return signal? Are you saying that the Suburban design uses the spark apparatus as double duty for whether or not the flame lit? If true, that seems dumb.

There does not appear to be any damage to the orange wire, looks new. The connection to the lug is shiny and clean.

As suggested, I cleaned the burner tube. The air-gas mixture is fixed, not adjustable.

Not only does Suburban but also Atwood/Dometic, Norcold for water heaters, fridges, furnaces etc

And it is VERY Smart technology
When the Flame ignites ti creates a current (Flame Rectification)
Flame generated AC Current is rectified into a DC Current which the circuit board senses via the milliamp signal thru the Spark Electrode.
All this takes place w/o further devices/equipment/sensors and happens within seconds of gas valve opening/spark electrode firing
No flame proving signal....circuit board shuts down DC to gas valve---hence no excess raw fuel

My understanding is that the flame conducts electricity between the flame sensor and burner. In doing so the current is changed from AC to modified DC, hence the term rectification. However, since the supplied electricity to the heater in an RV is already DC, how can there be rectification?

The crimps, mentioned by Gary, are in the area of the ECO and thermostat. Couple are hidden behind shrink tube enclosing thermal fuse.

If the board is not a potted board you can remove it and look at the reverse side for and burnt or discolored solder tracks. While it is out you can try cleaning the contacts also. If it is a potted board it can be checked with a multi meter. Attwood has a guide on their web site, Suburban should also. If problem is intermittent check the ground that Bud mentioned this fixed my issue before. I had this intermittent issue similar to yours where it worked sometimes and not others. Sometimes I would get 12v to the board and sometimes nothing. It drove me crazy for a long time. Every time I would check the brown 12v wire it would read 12v, then when I checked it at the board sometimes it was fine other times it was bad. What it turned out to be was a loose crimp. When I closed the door, the door hit the brown wire sometimes loosing the 12v supply. Re crimped a new terminal and all was good again.

Check for a good ground.
The gas valve coils have a ground connection behind the gas valve.
There is a ground coming through the wiring harness as well.
I cleaned the valve ground and connected the harness ground to it with a short piece of #14 SAE black wire
Did you clean the contacts on the circuit board?