Low Water Cutoff

wpmike

I have an oil fired steam boiler that is about 3 years old. It is Burnham V8H, the Low Water Cut-off ( LWCO ) is a McDonnell & Miller PSE-801-120. The problem I have is the water can be cold to lukewarm and the boiler comes on and few minutes later the boiler will stop because the LWCO has tripped, after a minute or two the boiler will restart. It may does this one more time and then it will run normally / non-stop.

What I have done to troubleshoot / fix:

1. I thought the LWCO might have been defective and got the exact same model and swapped it out, including the probe that screws into the boiler.

2. I skimmed the boiler, read this could cause the tripping.

3. I also read a bad ground may cause the tripping, I attached a copper wire from the probe to the boiler. You can see the wire in attached photo. LWCO still trips.

I have read some LWCO modules purposely trip by design, reading the specs on this model this is not one of them.

I am out of ideas of why this might be happening. Can anyone out there provide any suggestions for a fix? Attaching some photos of the boiler.

Fred

When the boiler is running, does the water in the sight glass bounce a lot and even drop to within an inch of the bottom of the glass? I can tell you from experience that Burnham boilers are more sensitive to oils in the water than about any other boiler I've seen. I can also see, from your sight glass that more skimming is needed. You have to skim very very slowly and maybe for several hours, multiple times. Do a real skim. Draining water from the drain is not a skim. The oils sitting on the surface of the boiler water is actually causing the boiler water to push back into the wet returns.

wpmike

The LWCO trips within a couple minutes of startup, the water has not even reached the boiling point, so there is not any surging at that point. Once the boiler is producing steam I do see some surging on the sight glass. But not where it will drop within an inch from the bottom.

I skimmed from a rear valve that is located about midway on the boiler, so I was removing any contamination on the water surface. The sight glass itself is dirty I need take it apart to clean it, on the to-do list. But I will take your advice, I skimmed for about an hour, but I will skim for several hours.

Fred

There could be oils on that LWCO probe, from not being fully skimmed.

wpmike

When I swapped out the LWCO I also replaced the probe, I did the skimming before this I replaced the probe. But like you said I may not have skimmed long enough.

About skimming, some have suggested running the boiler for a few minutes to heat the water and then start skimming. Others say do it while the water is cold. Any suggestion?

Also any ideas why the LWCO trips on initial startup but not once the boiler begins creating steam?

Thank you Fred your advice.

Neild5

When the boiler starts up and the LWCO trips is the water level still the same or has it dropped? Also do you have an auto fill ?

wpmike

For instance at this time of year the I may use the boiler in the morning to take the chill out of the house. So the water is fairly cold. The boiler fires and yes the water level does not move at all. But the LWCO will trip. There is an auto fill but it does not activate. After a minute or two the LWCO will reset itself and the boiler fires again.

BTW I tested the auto fill, I open the drain valve, until the LWCO tripped and the auto fill began to add water.

Fred

Have you looked at the manual for that LWCO? It may do a self test on start-up. There may also be some dip switches in the unit that gives you some options to eliminate that but, if it does self test, that's a good feature to keep since it only does it on start-up.

JUGHNE

Is your boiler circuit solidly grounded?
This would be from the electrical panel all the way to the boiler itself. Bare copper or green wire. The sheet metal of the jacket would be considered an iffy/maybe grounding circuit.

Perhaps the oil burner ignition circuit is confusing the probe for the first start in the morning.....then something changes.

EBEBRATT-Ed

@wpmike,

Just for fun add an 1 1/2" of water to the boiler and see what happens. Just something to try but may not want to keep the water that high permanently

Had the same issue with a Peerless boiler. The tapping they give you for the low water control is too high in my opinion. Look in the boiler spec sheet. That's going to cut the burner off when the water level is at 1/3 of a glass. You could rip it out and put in a M?M #67

wpmike

@EBEBRATT-Ed I agree with you the tapping for the LWCO does seem rather high, but that is how it is designed.

@JUGHNE, yes I did ground it to the jacket of the boiler, not optimal but it was more of test to see if cycling would have stopped or lessen.

@FRED I looked thur the documentation this LWCO does not have a self test. I can't understand this thinking, contractors go thur a lot of trouble to prevent short cycling of equipment. And this "feature" causes cycling....

But I took Fred's advice and I am doing a more extensive skimming. I need to remove the probe and clean it, in case there is any residue on it.