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Help on Water Replacement Unit Repair

I'm quite glad I stumbled across the site, and will be ordering the books!

Last weekend when I pushed down the blowdown valve lever to drain the sludge from my single-pipe steam system, the handle broke off. Lo and behold, on the back side of the refill water tank, against the wall, where I never can see, the blow-down valve was utterly devastated by corrosion/rust. The visible part, of course, was fine.

At any rate, we needed the furnace to work, and after I banged on the valve to dislodge rust the gasket seal was compromised. 3 screw heads were gone, so resealing wasn't an option. An HVAC guy on a Saturday night would quite possibly (likely?) not have a part, and would certainly be pricier than this unemployed computer geek can afford right now. So I ran to Home Depot before it closed, cut an aluminum plate, drilled screw holes, cut and fitted a gasket, and created a temporary patch. Doesn't even leak!

Having done my research, I now know that the water refill/low water cutoff unit is a McDonnell Miller 47-2.

I have the following situation:

1) I got 2 of the 3 headless screws out with pliers and WD40, but one is stuck. I have not yet tried to drill and tap the remnants of the screw, a task I've never attempted.

2) Replacement valve + cartridge/strainer kit (I assume that should also be replaced at the same time) will run me a bit over $200.

3) Starting yesterday, I have a dribble of water coming from an air vent valve on a pipe right next to the boiler -- I'm 95% sure it's the return water pipe. It only dribbles when the system is active, and the water coming out is tepid.

4) I found a source for a complete 47-2 unit, new in the box, for $375 shipped.

My questions:

1) Is there any reason to think the dribble issue will take more than replacing the vent/valve?

2) What other parts, if any, should be checked/periodically replaced in the 47-2 water replacer/low water cutoff?

3) Would attaching the blowdown valve with 3 screws instead of 4 compromise the system? 3 has been more than adequate for the temporary patch I put on.

4) Given that it's been installed at least 5 years (time I've owned the house), and since I'm having difficulty getting that broken screw out, would it make sense to buy the whole 47-2 for $370, instead of just the valve and cartridge/strainer for $200?

4a) What's the time and difficulty difference between the two tasks if I need to do it myself? What's the difference in labor cost likely to be if I get a pro in to do the work?

Thanks in Advance for any help,



  • Unknown
    edited February 2010
    Some Things are Better Left to a Pro

    You really need to get a steam pro to look at your boiler. Safety devices are not something an amateur should play around with and it also would concern me that since this unit has failed, what other items are non functional or a potential hazard. "Mickey Mousing" safety devices is just plain DANGEROUS!

     While it sounds like you are pretty handy, safety items aren't something that you would want to mess around with or mickey mouse especially as you are obviously new to steam systems. ( Boilers make steam, Furnaces make hot air) Since you know computers, this would be like allowing my wife, who is "technically challenged", to fix my lap top, The only difference being that I would just have to buy another laptop where as a boiler has the potential of blowing up the whole building!

    One of the rules on this website is we don't discuss pricing so I'm afraid I can't help you with that. There is a good reason for this but I won't go into it here.  Try "Find a Professional" at the top of this page and see if you can't find someone local to you. Don't use the zipcode function as it still has some "bugs" (software is new)  Scroll down the page till you find your "state" and look under that. There are a lot of good guys listed there.


    While I can appreciate where having a breakdown happen at this time might be an economic burden, I think you need to have it fixed by a pro, then get the books and  you'll be able to save by being able to do a lot of your own general maintenance in the future.

    Good Luck!

    - Rod
This discussion has been closed.