Old Weil-Mclain Boiler No response.

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879000#Comment_1879000

Thanks for this info!

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879010#Comment_1879010

It's powered by 24 V, I traced every wire in that mess, lol.

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879012#Comment_1879012

I will, when I get a chance, thanks for the concern!

109A_5

That is an older LWCO. Nice and simple.

I believe the 24 VAC input voltage is stepped up to a higher voltage for the probe circuit. When water is present the current through the probe and the boiler water energizes the relay. If the water level is low the relay will drop out (or never energize) disabling the burner. If power to the LWCO is missing the relay will never energize so the burner will be disabled.

If the power is present to the LWCO and the boiler water becomes low the probe voltage will be higher (in reference to ground). This will cause the relay to drop out and I presently believe it will light the lamp (probably neon) on top of the LWCO unit.

What does the note say on top of the LWCO ?

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879018#Comment_1879018

If the input voltage is stepped up it must happen inside the LWCO because I traced the wires back to 24V source. There's only 1 wire connected to the probe so I think you are right that current must flow through water to activate the safety chain somehow? I can't take the probe out yet, seized in place.

The note on the LWCO says something like "the red light will lit when water is low".

109A_5

Yes that is what the transformer is for. The 24 VAC power to the LWCO should be verified, the Black and Green wires. IMO the basic operation of the LWCO electrical part could be verified. Wire to the probe under the wing nut disconnected the burner should not work and the light is on. If the probe wire is grounded the burner should work. Make any changes for tests with the power off since there may be high voltage at the probe wiring connection.

109A_5

The LWCO relay is under the metal cover just above the probe wing nut connection.

EBEBRATT-Ed

Just put a big wrench on the probe well it will come out

EBEBRATT-Ed

When you put it back in use pipe dope or Never Seize available at an auto parts store it will make it easy next time. No teflon tape.

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879024#Comment_1879024

Ah that makes sense. Didn't realize there's a built-in transformer! I'll test more if it still doesn't work after i dealt with the probe.

Thanks!

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879029#Comment_1879029

Big wrench and pipe dope yeap. I took it off today, much easier after 1 day of penetrating oil. It looks like coated very evenly with this copper color stuff. I'm not sure if i should sand it off. But the color does look like this silicone boiler additive that i was told to add every 2 years by the previous owner. Also when i do continuity test with the multimeter, most parts on the probe doesn't make it beep when i had the other meter contact at the other end of the probe. Only beeps when touching the corners of the probe where the metal is a bit shinier.

I'm thinking the silicone additive finally covered up the probe over years and i need to sand it off.

What do you think? Thanks!

mattmia2

clean it with scotchbrite or steel wool. if it is plated with something nonconductive it likely won't work right.

since it is a safety device and it is like 30 years old it wouldn't be a terrible idea to just replace the whole lwco with a new safgard.

EBEBRATT-Ed

Or just replace the probe if available

109A_5

I'd clean the probe, kind of wonder if a newer style probe has enough surface area for the relay to energize properly, may depend on the water. The electrical part is dirt simple, no weird high tech issues when you need heat.

Daboosa

https://forum.heatinghelp.com/discussion/comment/1879161#Comment_1879161

I cleaned the probe and it's conductive again, confirmed by continuity test. Still has problem though.

When the power is on and water is low, the warning light lit up. When water reach the probe, the light turn off. I guess it means the probe is working? However, when heat is called, boiler still won't respond. If i jump terminal 3 and 4 (the label on my hand drew diagram) when heat is called, boiler fire up. So the problem must still be the lwco.

I tested continuity between terminal 3-4, 3-5, 4-5. No call to heat, power off or power on, there's only continuity between 3-5. That means the bimetal switch is not shifting position to connect the safety circuit if i understand correctly.

When the power is on, the voltage between 6-7 is 148v, between 6-8 is 138v, between 7-8 is 10v.

Do you know what's the circuit inside the bimetal relay box? I took a guess and drew a diagram. It's riveted in place so i can't easily take is off.

What other test can i do to diagnose?

I know it's probably time to get a new lwco but I'm curious also still confused about a few things. For example, I don't understand the circuit connecting the warning light and the probe, and the possible heating element on the bi-metal switch. Maybe I drew it wrong.

Thanks!