Old Mcdonnell Miller Round Port Model 47-2 plugged

PMJ

Did first firing today, checking controls found no water will come through at all. Seems discharge side after valve plugged. Valve operation itself seems OK looking up from bottom. Just can't blow through it.

Can it be cleaned out? Any suggestions? Kept boiler full last season though system doesn't use much.

nicholas bonham-carter

Is it the makeup water which is not flowing, when you blow the LWCO down, or is boiler water not flowing into the chamber?
First see if there is a valve in the line supplying this unit, which may have been turned off. If that is not the case, then study the diagram below, and get any replacement parts you may need, before this repair, as the boiler will be off until this is fixed. Switch off the boiler, and turn off the water supply to this.
In the makeup valve, there is a strainer which may have become plugged, and will need to be replaced.
http://www.boilersupplies.com/mmiller/docs/47-47-2_Parts.pdf
NBC

PMJ

The LWCO works fine. It is the makeup valve that is not allowing water to pass. I know there is pressure makeup water coming to it. Cleaned the strainer - thought that might be it but it wasn't. I unscrewed the two unions and removed the whole valve from the LWCO. I hooked up the discharge side union to the supply line, cracked the valve and water did flow through it backwards. I figured it should work then and reassembled everything but still no flow. Linkage connection to LWCO float appears to operate fine.

Abracadabra

Check the cartridge. Might be something blocking the flow at the seat. If it's an older round port valve, you may have to replace it with the newer hex port valve, which will get you a new strainer too.

Is the cartridge connected backwards? You said water flows thru it backwards... I'm not 100% sure it's supposed to do that. IIRC, the valve won't let water pass thru it backwards, so maybe it's backwards? *shrug*

PMJ

I ordered the hex port replacement. Not sure if this one was original with the boiler which was installed in the 50's. It has been there at least the 22 years I have.

Anyway, it has done a great job and now not worth any uncertainty. I will just replace it.