HB Smith Boiler adapted to old piped system

Chris Rubbicco

First off I replaced an old coal-fired boiler that had a retrofit oil burner attached. It was approximately 5 ft high and severely rusting and had inner tank section-to-section leakage. The replacement boiler was a Series 8 HB Smith. This boiler has got to be way less than half the water volume of the old boiler. All the cast iron radiators are single piped so I believe this is a single piped system. I did this replacement back in 1994.

The piping arrangement I used was the same as the old boiler and is described like this.
A 3 inch supply line come off of the top of the new boiler and goes up about 4 feet to a tee that branches out 6 inches on either side to 2 elbows. This forms two 3" parallel steam headers that proceed down the middle of the basement for some 20 ft to one end before disappearing into the overhead to supply various radiators throughout the house (6 or 7 in all)
At the point where the steam supply piping turn upward from the basement and into the house are two 1.5" connections at the 3" elbows to form what I believe is condensate drain headers, both parallel and directly below the supply headers proceeding back to boiler the same 20 feet where I piped it down and into the bottom of the boiler with makeup water supply. I first put in a crossover pipe to satisfy the Hartford loop requirements from the supply to the drain since they were in close proximity of each other. This produced water hammer upstairs in the house so I quickly removed it. Heating continued for many years with the only problem being the low water cutoff float sometimes actuating a low water condition. I think this was due to boiler water level surging and sometimes the low water cutoff would not reset unless you tapped it.
Well 10 years later, this last fall, I finally broke down and installed an electronic low water cutoff. It seemed to work consistently and reliably. I installed in a hole in the left side plate for the tankless water heater. There was a plug in the front of the boiler I believe to be used for the same purpose but the plug would not come out. Since the cover plate for the tankless was severely rusted and leaking I used the 3/4" hole provided with the new plate. This hole was at the same level as the low water cutoff any way so it seemed the logical choice. Testing the system it proved to turn off the burner at the correct level.
Now my problem. Two days ago with all this cold weather my mother went down stairs to check on the boiler to find no level in the sight glass but the boiler was still firing. She immediately filled it up for what she said seemed like a few minutes before level finally reached the middle of the sight glass. Later when the burner turned off and boiling stopped all the water came back and flooded the sight glass and boiler. I tested the system for a solid day in the fall and this did not happen then. The boiler pressure cycles between 12 and 9 psig. I believe this maybe a contributing factor but the pressure switch was delivered at that setting attached to the boiler so I didn't mess with it. However, I read that the low setting should be .5 psig with cutoff at 2.5 psig for optimum operation. Not sure that is enough pressure to flow into the house. Also when the sight glass was empty why didn't the burner turn off. Is the probe somehow being wetted by boiling in the unit or the sight glass showing level incorrectly? I just installed it so I can't believe it is malfunctioning already.
What are my problems here??

Sincerely,
Chris

EBEBRATT-Ed

Sounds like a lot of problems. You have to get the steam pressure down to 2.5 or lower. If the burner short cycles you are probably firing to hard and need less input-smaller nozzle etc. You need the hartford loop because the steam pressure is forcing the water out of the boiler and into the returns. NEVER PUT WATER INTO A HOT BOILER WITH THE BURNER FIRING IF NO WATER IN THE GAGE GLASS. Remove and clean the gage glass and connections and make sure the low water control is mounted above the bottom of the lower gage glass tapping. Make sure it is wired correctly and that it works. Call a professional if need be for the above.
This is just for starters!

Steamhead

The old boiler

could use that piping arrangement because it had a big steam chest. The new one doesn't, so it needs better piping than it now has. This is especially important on a counterflow system like yours.

The problem with the LWCO may be a dirty probe. Wet dirt could cause a short-circuit making the LWCO think there's water in the boiler when there really isn't. Take it out, check it and clean it if needed.

Crank the Pressuretrol down as far as it will go. More pressure means more steam generated than necessary, which means the water level will drop more than needed. If this results in uneven heating, you have an air venting problem.

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