Low water cut off

Pgarland2020

Have a leak from low water cut off. Can rusted piece with leak on bottom be replaced or do I need a whole new system. Photo attached.

109A_5

Hello @Pgarland2020,
Almost looks to me as if it is leaking up higher at the gasket from the switch assembly and not down by the blowdown valve (both are rusty).
Anyway if you are handy and ambitious the parts and gaskets are available to repair either issue. Supplyhouse.com or other vendors also eBay. If I had the switch assembly off to repair the leak I would also clean out the rust from the float chamber and carefully clean the float and the sylphon or bellows (messy job, cleaning and removing the old gasket). I make my gaskets from thin silicone rubber sheet material for easy future gasket removal. Many Youtube videos if you want to see what it is all about ahead of time.

If you call a Pro they may just replace the whole M&M 67 LWCO. M&M recommends it be replaced every 10 years, mine is about 50 years old and works fine.

EdTheHeaterMan

Any part that is rusted can be removed and replaced with a new one that is not covered in rust. You can pay dearly for a professional plumber to do it, or you can do it yourself if you have a big enough wrench.

Just look at YouTube videos on how to remove rusted pipes, How to service McDonald & Miller #67 LWCO, Proper ways to install threaded pipes and fittings, and other related stuff. You will save a ton of ca$h with the DIY method. If you are not mechanically inclined, then you are at the mercy of the plumbers.

Good Luck with your project

ethicalpaul

If anyone's life other than yours could be affected by a fire in the boiler room caused by LWCO failure, replace it.

EBEBRATT-Ed

Install a new one and make sure it works and shuts the burner down when you drain it. The $500 you spend for a new one may save your boiler or worse.

EdTheHeaterMan

EBEBRATT-Ed said:

Install a new one and make sure it works and shuts the burner down when you drain it. The $500 you spend for a new one may save your boiler or worse.

What plumber is going to replace a M&M #67 LWCO for $500.00 when the thing costs more than that? And I was referring to the rusted pipe fittings that appear to be connected to the boiler just behind the LWCO. If this boiler owner is going to need to call a Pro, They need to be prepared for a 4 figure quote, and the first number will be somewhat higher then $1, maybe even higher that $2, . if the piping behind the LWCO is included in the repair.

ethicalpaul

But if they don't replace it there will be significant labor involved in rebuilding it anyway. And the rebuild might fail necessitating replacement anyway. I'm cheap as hell but I say replace it, unless the boiler has a hole in it.

EdTheHeaterMan

I agree with replacing the #67 and the #47 LWCO at certain intervals, As long as they have been flushed properly each week. If it has been neglected for a few years, then I would NOT spend the time cleaning it out. Mostly because my labor to do it properly would cost too much, compared to replacing it and having a 10 year old rebuilt part when completed. But I would take one apart and do a deep cleaning and install new gaskets and flush valve every 5 years or so. Then make a judgment call as to the need for a new replacement or keel the existing.

I have been looking for a story or video that has a #67 that would appear to operate properly on a flush (because the fast flow of the water past the float forced the switch off) but failed to shut off the burner when the water level dropped slowly as it might during normal operation.
That was because there was a small mound of build up on the ledge that the float would get stuck on, and that flushing failed to remove. I believe it was @DanHolohan who published it but I just can't find it. I stole this pic from Gordo to illustrate how the fast moving water in the flush didn’t move all the schmutz outta the way. (schmutz is a technical term)

Probably because the flush was not done with high enough steam pressure

DanHolohan

I can’t find it either, Ed. But I got that from the factory people many years ago, and it is so true. They would tell me that we have to blow down the unit first slowly to see if it works and then quickly. Just blowing it down quickly can hide the fact that the build-up on the bellows is there, and that can cause the unit to not cutoff on a slow leak. 

john123

Is this a steam system? Are LWCO different steam system
if it is a water system, could the answer be installing brand new one of the newer versions of LWCO which seem much cheaper?

STEAM DOCTOR

Steam system