Flame rectification

mburg

I have a Weil McLain boiler model: HE 2-4, it is sidewall vented. The boiler will fire burners for 1-10 minutes and than the burners will shut off. I assume that for whatever reason it’s not proving flame. There is hot surface ignition, but no flame sensor. Could anyone explain how flame rectification works on a boiler that does not have a flame sensor, also any ideas on what is causing this issue? 

Ironman

I believe they use the HSI to detect the flame and there have been some issues with it.
But, you may have something else wrong.

@Tim McElwain is the one who would know the particulars about it.

JUGHNE

Your HSI has two jobs....light the gas and then report back that there is an actual flame present to keep the gas valve on.

The first job is easy, it just has to get glowing red hot and stay that way as the 120 volt to it is switched off as the gas valve opens. The after glow is what lights the gas.

Then the circuit purpose changes to a detection circuit.
A small AC current is sent thru the HSI, if that AC travels thru the flame of fire it is rectified to Direct current (DC) that the control module recognizes as the presence of fire and it is safe to leave the gas valve on. If the DC (microamps) is lost then the gas is off almost immediately.

The HSI gets somewhat crusty over the years of being in the fire and may not be able to conduct the correct microamps to communicate with the control module.

As with any electric circuit there has to be 2 pathways/conductors to complete the circuit.
One of them is the HSI itself and the other is a ground path of the burners back to the ground on the control module.

IIWM, I would first check the grounding path to the control.
Just pulling and resetting the spade terminals may cut thru any corrosion.
The grounding of the boiler supply is critical also, maybe something loose there.

If assured of a good ground path then I would go for a new HSI.
It has been there for a few years. I would not try to clean it much as they are very fragile, especially as they age.

IIWM, that would be the first things to do.
Replacing the HSI is sometimes part of preventive maintenance work. You will eventually need a new one anyway.

mattmia2

if the current is through the burner to the chassis of the boiler to the controller, why does it need to be grounded?

nicholas bonham-carter

1 to 10 minutes burn time seems too long for an ignition failure, so maybe another safety device is cutting off the burner.
Is this steam or hot water?—NBC

mattmia2

nicholas bonham-carter said:

1 to 10 minutes burn time seems too long for an ignition failure, so maybe another safety device is cutting off the burner.
Is this steam or hot water?—NBC

unless something is intermittent and failing with temperature, probably a connection somewhere, either the wiring, ground path, or something in the control itself (possibly an easy to fix solder joint). easy enough to measure ac voltage across the contacts of the various parts of the safety controls and see if you measure very close to 0 vac indicating the contacts are closed or 24 vac indicating something is opening.

motoguy128

HSI’s have a finite life anyway. Start with replacing it, but as mentioned also check grounding.

The residential gas furnace industry and boilers went away from them for that reason, or because of size and cost. Most everything is now spark ignition except gas appliances like ovens. Those seem to still be HSI’s.

mburg

No other safety’s where tripping out, all lights on board for safety’s remained lit the entire time. I also checked voltage at switches. The burner itself was the only thing that cycles. I assume it’s either a grounding issue or a issue with the hot surface ignitior. When checking grounding should I be looking at ground from panel box to boiler chassis? This is a hot water boiler. Is there any way to check the flame current like you would if there was a flame rod? 

JUGHNE

The grounding from the panel box to boiler is important from a safety standpoint. It or lack of it may affect some flame rectification systems.
The ground path for the flame detection is all within the boiler itself. It needs to go from the burner back to the module.
If the chassis is relied upon for that path, then time and corrosion may introduce some high resistance in that pathway.
Also as the boiler heats up expansion of parts may compound the contact.

Some burners have a ground wire to insure continuity, I have added ground wires from the burner to the module ground connection point.
Some modules use one of the mounting screws to make the ground connection to the chassis. Those have an obvious metal contact plate under the screw. Just loosening and tightening that screw cuts a new pathway for grounding....if it of that design.


As far as measuring the microamps for the HSI, I don't know of a method unless the module has test ports.
The HSI starts out with 120vac and then it's function changes to a supervision circuit.

All this being said, I would just check the wiring connections and then change the HSI.

ratio

Use one of these to measure µamps with any meter that will read DC volts. I like them because they interpose between my expensive meter & I can leave 'em in position (don't interrupt the flame signal) while I use the meter for other tests.

Tim McElwain

It is usually a simple process of changing the igniter first. Nine times out of ten that will solve the problem on this system.

If you want to measure microamps go to the nine pin harness on the 1013-200 and disconnect the # 6 wire (usually yellow) and connect your microamp meter between pin 6 and the wire you removed from pin #6. You should have between 2 to 10 microamps.

Tim McElwain

Try this for troubleshooting: https://www.weil-mclain.com/sites/default/files/field-file/he-ii-hsi-control-supplement_1.pdf

Tim McElwain

The complete troubleshooting procedure for the 1013-200 is located in the manuals for the Weil McLain Gold boiler but it is up to date compared to info on the HE. https://www.weil-mclain.com/sites/default/files/field-file/gv-series-4-manual_1.pdf

mburg

Thank you so much for all this help!  I should be able to make a educated repair on this now! 

mburg

Also Tim, I would be interested in purchasing some of your books, but wasn’t sure where I could get ahold of them? 

Tim McElwain

Contact me at my e-mail address timmcelwain@gastcri.com and I will send you a catalog.