Boiler blowdown issue

Dollr

Hello all. I have steam heat (Peerless boiler and milivolt system) and it has worked very well for the 24 years we've owned the house. This blowdown issue just started. I blowdown the boiler as usual. The burner cuts off and then the water feed replaces the discharged water as usual. But now the burner doesn't come back on and the pilot light also goes out. Any ideas on why this might be happening? Thanks.

Jamie Hall

I wonder if the low water cutout connections in the LWCO are worn or sticking open.

Dollr

Thanks for the reply Jamie. That seems likely. The LWCO is one of those McDonnell and Miller ones. I don't know anything about them. Are they serviceable? Are parts available for replacement? The LWCO is pretty old (installed 1990) but it's been reliable. Thanks again.

delcrossv

The pilot shouldn't go out even if the LWCO is having issues.

Chris_L

It sounds like the boiler is not coming back on because the pilot went out. You need to find out why. (Not sure what the LWCO would have to do with that.)

Is this really a millivolt system? (I see a AC outlet on the boiler.) If you have a millivolt gas valve, a trip of the secondary Pressuretrolwill turn it off.

109A_5

Hello Dollr,

Can you take pictures of the other sides of the boiler ? Looks to me like it is a 24 VAC system, which in that case maybe the thermocouple quit and the pilot went out.

If the M&M 67 is actually the issue, rust may have not allowed the float to return to the top of the chamber, but that should only keep the burner from coming back on, and should not affect the pilot. The M&M 67 can be disassembled relatively easily to clean the chamber and float, it may need a new gasket when reassembled, replacing the M&M 67 is expensive IMO.

Dollr

Ok, thanks for all the comments. Here is a close up of the LWCO says to be used on milivolt system. So, seems to be that? Maybe a bad thermocouple? Or? Thanks

Dollr

Ok, here are a few more photos from different angles. (I know the header isn't right but it works fine) Good to hear the the LWCO is relatively easy to clean out if needed. I do try to keep the system clean. Thanks for the help.

Intplm.

That flame on that thermocouple looks good. Seems to be holding the flame well. How long has that thermocouple been there. Is it twenty four years old too. You should get the boiler serviced. Seems you have two problems in the lwco and the thermocouple.

Dollr

I think the thermocouple was replaced about 5 or 6 years ago? Not much longer than that. Not too old. I'll need to get someone over here and check things. Any recommendations on where they might start? I guess the LWCO and the thermocouple? Anything else to look at? Thanks again.

Intplm.

Have a qualified company come by and do a full service on the boiler. They should fix the two issues that you have and they should get a good look then for anything else.

109A_5

To me it looks like a Millivolt (Power Pile) / 24 Volt hybrid system, not a thermocouple type, would need more pictures of the wiring to confirm. The Millivolt (Power Pile) runs the gas valve and the LWCO may be in that circuit. The 24 Volt AC circuit is probably for the thermostat and a relay that controls the Millivolt (Power Pile) circuit. The pressuretrols maybe one on each circuit, hard to see.

The cover at the Red arrows comes off and there is 4 screw terminals I believe the upper two are for the LWCO functionality and the lower two are for the water feeder. If the LWCO float has a rust sticking issue or the switch failed jumping the upper two terminals will cause the burner to start up. The switch is removed to access the float assembly removal to clean the inside of the housing and the float. Basically just a screw driver, a gasket scraper, utility knife and a small wire brush is needed and maybe a new gasket to reassemble. Careful with the Sylphon it is delicate and the switch housing is also delicate do not over tighten the mounting screws. There are many Youtube videos on the subject.

Dollr

Thank you 109A_5. I believe that your assessment of my system is accurate. You said, "To me it looks like a Millivolt (Power Pile) / 24 Volt hybrid system, not a thermocouple type, would need more pictures of the wiring to confirm. The Millivolt (Power Pile) runs the gas valve and the LWCO may be in that circuit. The 24 Volt AC circuit is probably for the thermostat and a relay that controls the Millivolt (Power Pile) circuit. The pressuretrols maybe one on each circuit, hard to see."

Here is another photo showing the control side of the boiler if it helps. In the photo the cable going up and off to the right and out of the picture leads to the 24V water feed. I couldn't fit that into the picture. Thank you also for the detailed information on the LWCO cleaning and wiring diagram. Much appreciated. Right now I believe that this is the area that is causing the problem. I'll get someone to take a look.

Edit** Looks like the photo didn't upload. Try again.