LWCO short cycling the boiler....Is the mud leg clogged?

Jack M

The low water cut-off is short-cycling the steam boiler. After the LWCO stops the boiler, the water level returns to normal and the boiler starts up again. When I open the gate valve at the base of the boiler (near the mud leg) the water flows out perfectly clear (zero rust). This is a manual fill (not automatic) classic M&M (McDonnell & Miller) float type LWCO that gets flushed weekly. Why has the steam stopped returning to the boiler? Nothing has changed in this system in 10 years, and recent demand on the system has been moderate with temps in the 40s.

Jamie Hall

Has the condensate stopped returning? Or is just very slow returning? Two completely different problems. If it has stopped returning (you are having to add water) you have a leak. Find it. If it's just slow returning, then the wet returns need to be flushed out.

Jack M

No need to add water. Condensate is very slow returning. How do best flush the wet return?
That gate valve at the base of the boiler is the low point in the system (one-pipe system/everything insulated).
I could drain the boiler completely. Go to the main vent and hook up a hose in that location (or just shove it in the hole), then open the valve near the boiler connected to the return piping and see what happens. Better options?
Does a wet return typically clog because the iron pipe is rusting away internally or because of sediment?
.

Jamie Hall

Quite impossible to say without actually seeing the piping layout. There might be a handy drain valve.or valves. There might be a plugged T or two. You might have to disassemble a union somewhere. But however you get at it, it's necessary to run a hose in and flush out the gunk.

Jack M

The wet return is 1 1/2" black pipe with one union. Not sure if a snake would go around that 90 degree

Jamie Hall

In the picture with the vents, does that pipe going down go all the way down to the wet return? If so, you can take the antler off and try running water in there with the drain valve open. Note that if the drain valve doesn't flow, you'll need to get something in there -- a wire? -- to dislodge the sludge plugging it. You may even have to open the union to get things cleared.

reggi

@Jamie Hall  You have better eyes on it than I do so what about getting rid of that valve and putting on a Full port ball valve to get a full opening and get another entry to run a wire or back flush with a hose ?? ( Gently with care of course at low stream)

Jack M

Instead of removing the antler (to run water through), could I just open the "water fill" for the boiler and let the water fill the boiler, fill the riser, and fill the steam pipes around the loop back to the wet return (not filling the radiators). Will that flush the wet return?

Mad Dog_2

That's why on My Antique Vapor system I installed 45s at all turns, with Full tees on the ends with bushings so I could rod out the wet returns.  Mad Dog

JUGHNE

I would remove the main air vents and also the upper pipe so when water came out of there you stop overfilling, then you could try your entire pipe flush.

However is you have some borderline pipe hangers, remember you are adding weight to the load on those hangers.

You do not want the water to back up into the rads.
Once the main is filled it will take a short time to overfill the system.

The boiler drain you have is very restrictive to pass any amount of sludge and may plug quickly. A full port ball valve with hose adaptor is recommended.

Jack M

I would love a full port valve, and another at that 90 degree bend so that I could easily access the wet return.

Jamie Hall

Jack M said:

I would love a full port valve, and another at that 90 degree bend so that I could easily access the wet return.

Or at least a plugged T instead of the 90... that's what you should have. How ambitious are you?

Jack M

Jack M said:

I would love a full port valve, and another at that 90 degree bend so that I could easily access the wet return.

At the moment, keeping the occupants happy is the priority. I will add "the T or port valve" to the "warm weather list", it would be nice to be able to easily flush the base of the boiler as well.

1. removed the antlers
   
2. flushed down where the antlers attached with a garden hose/nozzle/lots of pressure,
   
3. pushed everything out.
   
4. let the system cool for a few hours
   
5. with a cool boiler, I back-flushed the boiler via the fill.
   
6. refilled the boiler
   
7. reattached the antlers
   
8. fired it up.
   
9. crossed my fingers
   

reggi

@Jack M
5. What fill did you back flush the boiler from and where did it come out?

Jack M

reggi said:

@Jack M
5. What fill did you back flush the boiler from and where did it come out?

I use the term "backflush" loosely because all I did was open that gate valve at the base (shown in the previous photo) and turn on the "fill" for the boiler. I don't really have great access to that side of the boiler (installed very close to the chimney). When draining the boiler, all the water was crystal clear until the last quart drained out. That last quart showed a rusty residue (which may have moved down that clogged up wet return).

Jack M

Success. The system ran a full cycle and shut off on temperature (as it should). The water level in the sight gauge did not bounce but dropped one and a quarter inches (1 1/4"). The radiators filled all the sections completely and evenly (no screaming vents). The system overshoots the thermostat but it's always done that. I'll keep an eye on things to make sure the steam lines are not flushing sludge into that wet return. Hard not to love the comfort of steam radiators, like standing in the Florida sunshine.