Boiler overfilling and banging after running for several hours

jgover

Hello Folks,
I have a one-pipe steam system in a 800 sq. ft. rental townhouse with the following specs:

Slant/Fin boiler
#67 LWCO/ auto feeder
4 radiators

It has worked fine since I took ownership of the house in 2003.
In winter 2015, the tenants alerted me that one of the boilers was leaking. It is an old house, and I removed the boiler for repair. I still haven't put it back yet, trying to find time to fix a leak between sections with J-B Weld. It looked as if it had been repaired several years previous with epoxy. I am not sure if that has any bearing on the following problems.
Starting last spring, the tenants alerted me that there was significant banging throughout the house during the night. I retrained them with how to purge the LWCO, and to do this weekly. Then hot weather arrived and I did some tests on the system with the help of an experienced contractor. We tested the LWCO and fill for correct operation with no apparent issues. He recommended replacing the old relief valves, which I did with new Gortons. Over time, the system still overfilled and even leaked from upper floor radiators - when the system was off. My next step was to check the feed valves. I replaced the old gate valve on the feeder bypass with a new ball valve. I went and tested the system for one hour yesterday afternoon. Starting from cold boiler, house temp at ambient 58F, I turned on the boiler, water in sight glass at correct level. The boiler kicked on after 3 minute delay, then ran continuously for 15 minutes with no banging whatsoever. All radiators were hot and relief valves were functioning normally. For the next 20 minutes the boiler cycled on for a few minutes, then off for minute. I cannot remember if it is normal for it to short cycle like this, but in that time the auto-fill did not kick on, and the water in the sight glass remained constant. I turned the heat off after 30 minutes, the house temp had risen to 62F.
The tenant came home a few hours later and reported that the burner kicked on 10 minutes after he turned the heat on. He said it ran fine all night, until 5AM when he was awoken by banging throughout the house. He turned the heat off at that time so as not to wake the neighbors. The tenant reports that he did not notice the auto-feed kicking on, which is very noticeable in the house.
Please advise what I should do next?

Abracadabra

What's the water level when the banging happens?

jgover

The boiler was shut off at 5am when it started banging. I went to the house to check it at 3pm, and sight glass was full. I let out about 3/4 gallon and fired it up, no banging. It heated up perfectly in 15 minutes. Auto-fill did not kick in at all. It seems like something is happening during the night.
Has anyone ever had a problem with the auto-fill slow leaking water into the system? At this point, I think this must be the weakest link.

vaporvac

Do you have a DHW coil that could be leaking? Have you shut-off the fill valve?

Jamie Hall

It isn't that common, but any kind of valve can leak a bit -- and it doesn't take that much of a leak. Do try shutting the manual valve on the auto-fill off completely.

And then don't forget to check it from time to time, to see if you need to add water!

jgover

I do not have a DHW coil.
Over the summer when it was off, I shut off the water supply completely, and it did not flood. Did I mention that it was flooding in one week when the tenant was out of town and the boiler was on pilot only? It actually filled to the second floor and dripped out of the radiator relief valve. I have been thinking the auto-fill is leaking. Should I just replace that whole auto-fill valve?
I would like to turn off the supply now, but since I do not live there, I worry that if the LWCO fails...

Jamie Hall

A most valid concern. Tenants are not always the most reliable water level checkers, and if the it runs out of water and the tenant has no heat, they'll not be happy campers. If the LWCO fails and it runs out of water, they'll be even more annoyed.

I'd go ahead and replace the whole auto-fill.

nicholas bonham-carter

And the LWCO while you are at it, since that is the safety device.--NBC

Abracadabra

LWCO could be leaking... maybe there's some debris trapped in the seat of the valve?

jgover

So I should replace the LWCO and the auto-fill? Or just start with the auto-fill?

ChrisJ

If it didn't do anything with the supply shut off, but overfilled with the supply on and the boiler off wouldn't the problem obviously be a bad autofill?

The radiator vents and main vents are air vents, not relief valves. They allow air to escape so steam can fill the system. I'm only saying this as 'relief valve" can be confusing as it makes me picture the pressure relief on the boiler.

If it was mine and I knew without a doubt the #67 was clean and in good working order I'd replace or completely remote the autofill and go from there. What autofill is it? The Hydrolevel VXT is the only one I'd ever consider using on any boiler but make sure you configure it correctly for a mechanical LWCO. Maybe someone else knows for sure, but I believe there's a delay before feeding setting of sorts you can enable.


If the boiler is leaking don't bother patching it. The block is likely spent from taking in too much makeup water and then not firing immediately because of the LWCO and system leaks. You're going to find it's not just one area that is leaking or if it is, it'll be a lot worse in the near future. The VXT feeder has a water meter on it so you'll know if the system is using too much water. Personally, I'd be concerned about anything more than a gallon a month and only during very cold months. During mild weather you shouldn't have to add any.