LWCO float works intermittently - solved, and a question

McDonnell & Miller #61 on a steam system. Fought with this thing for the past week, though it had started acting up in the last week or two of the previous season. Standard start of year maintenance. Removed the switch from the fixed housing at its bolts. Outer housing cavity scrubbed free of sediment. Float is free of sludge, float moves easily, the pivot isn't binding up. The roller on the end that engages the arm on the switch spins freely. The levers on the switch do not bind. The microswitches that the lever pushes on snap back properly. Continuity is correct.

Install it back in the housing, fill with water. Doesn't work reliably at all. Sometimes the switches make and break, sometimes they don't. When you blow it down, it reliably cuts the burner, but sometimes when you close the valve, the furnace starts again, and sometimes it does not. Check continuity, the switch is open, even though the water is right. Remove the #11 switch, look at the roller that moves the switch, it's fine. Push on it with a finger, feel the float moving freely inside the housing. Move the switches with a finger, check continuity, No problem. Open the blowdown valve, float drops decisively. Push on the roller either direction, feel resistance as it displaces water, then it comes back to center as it should. Feels kind of sluggish, but it has to displace the water out of the way for it to move, so that seems ok.

Try the switch again, still completely unreliable.

Disassemble the whole mess again, everything still seems fine.

Disassemble further. Separate the switch mount and brass bellows from the cast iron part of the housing. Everything is fine. Brass bellows is fine, not caked with anything that would make it bind, pivot is still smooth and easy. Closely inspect the float body, no problems. It's caked with some dried on iron sediment on the dry half of the float, but that's to be expected, I don't want to scrub it too hard and risk damaging the copper float and its seals.

The… copper float… and its seals.

I set it in a big pot full of water. It doesn't float. It doesn't sink. It just kind of hovers there under the water like a submarine.

Hold it up to my ear and shake it.

slosh slosh slosh.

So while it has been responding to water level changes during a blowdown, it's not because it has been floating, but instead because the flow of the water moving downward when I blow down quickly sucks the float downward along with it. And when the water level equalizes, later, it does so slowly — sometimes fast enough that the water pushes the float up properly, sometimes it just kind of bobs there and settles wherever it feels like. When I flush all the start of year sludge, and the auto feed pump triggers, the water level rises incredibly slowly — never moving fast enough for the feed pump to trip off. It will fill happily keep feeding till the whole sight glass is full… Because the LWCO float and/or submarine is just sitting there, instead of responding to the rising water level.

Hopefully this helps someone in the future.