Where has all the water gone?

Jack M

Low water cutout shut down this Dunkirk (1970) boiler last night.
As the system cooled, the water level returned to full (on its own - no water added) and then everything ran normally.
The boiler is set up with a float type (manual) low water cut off ( flushed weekly).
In 14 years, the boiler has never shut off from low water (except when tested) . Could the wet return be sludged up? Could I tell if the wet return (mud leg)has a problem by feeling the temperature of the pipe?
I occasionally see some rusty water at the start of flushing the LWCO , but the sight glass is always clear.
This oil fired steam boiler is serviced annually but nobody ever flushes boilers these days. During annual service the tech vacuums out the boiler and smoke pipe, cleans the burner, replaces the nozzle and electrodes, changes the oil filter, checks the LWCO, flushes the fuel line, and runs a combustion test. After all that, it seem like a lot to ask to have the boiler and wet return flushed.
Where’s all this water going? If the wet return is sludged up should I expect to see a slight change in boiler pressure when steaming (an accurate low pressure gauge has been installed)? There's no bounce in the sight glass. Plenty of venting on the mains. When I open the tap at the base of the boiler the water drains clear.
It’s been a cold winter with more boiler run-time, but last night was not a cold night.

JUGHNE

1 or 2 pipe radiators? TRV's on radiators?
How much wet return do you have? (that would be any return pipe below the boiler water level line)
Pictures of wet return connection on back of boiler?
It is the usual suspect.

Jack M

• 1 pipe
  
• No TRV's on the radiators
  
• Wet return length of 6 feet horizontal black pipe
  
• no photo for now
  

Looking at the pipe it appears to have been replaced at some time the last 50 years. There is no separate clean-out on the wet return (The boiler and wet return would need to be drained together).

JUGHNE

Does your LWCO have an auto fill valve attached to it?
Or do you have the water supply valve shut off if it does?

When you test the LWCO the burner should be on and the test should shut off the fire......then if you have the auto fill it should add some water....you could hear it running.

Those returns commonly lay on the floor and then come up to the Hartford Loop. They are the lowest spot and collect sediment/sludge etc. That is a good thing as it keeps it out of the boiler.
The wet return may have a union or two that would allow you to remove it for flushing. Even though you drain the boiler the wet return section will have water in it.

nicholas bonham-carter

What is the exact pressure? Was the pigtail cleaned during the service?
Some wet returns can hold a lot of water if the pressure rises, and pushes the water out. In such cases, the water returns quickly. If it were a slow return, then I also suspect a clogged return.—NBC

Jack M

• no autofill on the LWCO (manual).
  
• LWCO does shut the boiler (works as it should).
  

The pigtail was not cleaned during service. I will do that.
I did not keep track of the time for the water level to return to normal. I waited 5 minutes and little happened and then came back in 30 minutes and it was full.
I rarely see the pressure gauge go much above .5 (PSI). With a really long run time (an hour) and all the radiators heated all the way across the gauge will climb as high as 1.2 or 1.3 and look like this:

EBEBRATT-Ed

It sounds like you technician is doing a decent job. Hold on to him. Cleaning and flushing the wet returns is not part of normal yearly service. If your wet returns are only 8 or 10' of pipe I would just replace them and not bother cleaning them. Just replace the pipe below the boiler water line.

The fact that all the water "came back" is a very good sign. Make sure the low water cutoff works and monitor the boiler and replace those returns as soon as the weather allows

Steamhead

Check to make sure all the radiator shutoff valves are open. if not, they'll keep water from returning until after the boiler shuts off.

Jack M

The return has two have two unions (shown with insulation removed). The joint on the upright (vertical) is sealed with some off-white joint compound (permanent seal?). Will I be able to break loosen that? The joint near the boiler on the horizontal pipe looks newer and is sealed with regular silicon tape. (sorry for the poor photos). Is there any way of knowing if wet return is sludged up without opening them? The horizontal pipe is 4.5 feet in length and is 1" pipe. No Hartford.

Jack M

Checked the pigtails and radiator valves. Everything was as is should be.

New England SteamWorks

EBEBRATT-Ed said:

Cleaning and flushing the wet returns is not part of normal yearly service.

It is for us!

New England SteamWorks

Sounds like your wet returns are clogging up. Not unusual.

JUGHNE

IIWM, I would drain the boiler, crack the unions, catch pan under the horizontal union. Loosen both and stuff newspaper twisted plugs in all openings. This stops dripping of tar water out and onto the floor. I would take it outside and flush water thru both ends. Some times the build up is such that it would almost require a sewer auger.
How about some pictures of the front angle showing the return and lack of a Hartford Loop connections.

Jack M

I kept an eye on the boiler overnite. While the water level in the site glass dropped a few inches, the level never triggered the LWCO. The pressure stayed below 1 psi (even when I let the radiators heat all the way across). So for now, I'm hoping its a flute and I can wait for spring to investigate the wet return. When I put an IR temp gauge on the wet return it measures 198 degrees F. The same temperature as most of the steam runs and header. So something is getting in there.

What is considered an acceptable or desirable drop in the water level when steaming?

Fred

The problem with "flukes" is they will happen again. Keep an eye on it and make doubly sure the LWCO works consistently until you find the issue. That water had to be hold up somewhere.

Jack M

What is considered an acceptable or desirable drop in the water level in the site glass when steaming?

Fred

Jack M said:

What is considered an acceptable or desirable drop in the water level in the site glass when steaming?

A lot depends on the size of the system, the length of the mains and run-outs as well as the length of the heating cycle. Generally, I would say if the water in the sight glass is no less than half the 'Normal" water level, and above the level that trips the Auto water feeder, you're fine. What is concerning, and the reason for my comment is that a fluke that causes a one time drop that shuts the boiler down warrants investigation and correction. You never want to leave home and not feel comfortable that the heating system might not do its job.

Jack M

I've been watching the water level. I think the "run times" on the boiler are longer than they need to be. The boiler overshoots the thermostat by six degrees (F). And instead of heating the radiators halfway across, I'm getting full radiators. Maybe there's an issue with the thermostat? If I could get some modulation on these temperature swings it would sure make life a lot easier on the boiler. The thermostat should be anticipating that when the pressure reaches .5 PSI that the radiators have enough BTUs to reach the desired thermostat setting (and shut down the boiler). Instead, the radiators are overshooting the temperature and every run cycle behaves like I'm running from a setback (because the boiler sits idle for so long). Perhaps this "deep setback effect" is why the boiler ran low on water that one night. Of course I'm just guessing and not ruling out the wet return as a culprit.
This is an old round Honeywell thermostat.

JUGHNE

If that tstat heat anticipator is set on .4 is should be the shortest run time. There is a good chance the heat anticipator rheostat windings are burnt. Try new tstat.

Fred

First off, the thermostat doesn't use pressure as a measure to determine when to shut the boiler down. The thermostat is driven by temp only. That's an old mercury thermostat. Is the Thermostat mounted level? If not, it may take a lot more temp for the mercury bulb to swing the contacts open to shut the boiler down. I think there are two little plastic tabs around the top of the thermostat to allow you to set a small level on them for leveling.

JUGHNE

Yes, Fred is correct (as usual). You should check the level of the mercury tstat. Then condemn it, maybe

Jack M

The thermostat looks to be level (eyeballing it). Some Honeywells have two leveling posts , however this one does not.
I did dust off the mercury bulb.

Fred

It is also possible the anticipator may be broken. A 6 degree swing is way too much. It may be time to replace the thermostat. If you get a digital one, just make sure it is programmable for multiple cycle settings, including "2" cycles per hour. Some of them go from "1" cycle to "3" cycles per hour.

EBEBRATT-Ed

@Jack M

Shut the boiler off. Take out the 3 screws that mount the thermostat to it's sub base. Once the stat is off the wall their is a flat spot on top of the sub base for your level