Steam Hammer on new (last year) boiler

Misterplumber

I am a heating contractor and have successfully installed many steam boilers over the years however there's this one boiler thats giving me a little trouble. I replaced this oil/steam boiler last year with a weil mclain gold with a tankless. I always replace the vents on the radiators and the main vents without fail whenever I replace a steam boiler. The old vents hadn't been changed in about 25 years. I have skimmed the boiler at least twice already.



The boiler runs fine however the customer is complaining about a deafening hammer that randomly happens on the opposite side of the house seemingly on the 2nd floor, mostly in the middle of the night when everyone is sleeping and it wakes up everyone in the house.



I myself have spent a quite a bit of time observing this boiler and haven't heard this phenomena. The customer said it never did this before I did the replacement.



The properties of steam obviously haven't changed, I haven't changed the main across the basement, and its not hammering near the boiler. I am wondering if I need to skim even more or if my changing the vents unleashed a problem that was concealed by a blocked vent all these years. And I also checked to make sure all the radiator valves are wide open. This one has me perplexed and any useful comments would be appreciated.



I don't believe the customer is lying as they have no reason to, they are close relatives of mine.

nicholas bonham-carter

mysterious water-hammer

do they use night setback? possibly after the low temp period, the thermostat calls for a big increase in heat, and therefore boils long enough to cause some weak spot in the system to show itself. get them to keep the heat off until you come over to listen as it recovers, or use a jumper on the thermostat wires to cause the boiler to run constantly.

this may be a sagged pipe in the returns which takes a while to fill up and hammer. we have one troublesome short horizontal line under the 2nd floor hall which i have permanently capped, as the effort of removing the floor to re-pitch would not be worth the trouble.

turning the vent upside down will prevent a given radiator from getting steam, and therefore serves as an identifying tell-tale in this case. if you can get it to bang,and then not bang, you can usually find the solution.

a search here for "hammer" will show many different causes of noise, discovered by people here, some of which have nothing to do with the pipes!!--nbc

Joe V_2

I agree with NBC

After installation of my boiler last year, a large night time set back would cause a loud hammer just before the alarm clock went off and then remain quiet for the rest of the day.  Reducing the setback eliminated the hammer.  I believe installing a vaporstat, in my case, will eliminate the problem regardless of the setback.

nicholas bonham-carter

steam detective work

i am always in favor of very low pressure, along with very, very generous main venting, so that there is no initial steam pressure on the risers until all the mains have been filled.

i wish i knew of some other tell-tale device which could be left on site, and then monitored later for water-hammer events. if the geologists can tell the location of an earthquake, including its depth, then maybe the same principles could be used for water-hammer detection!--nbc

Dave in QCA

Normal Water Level?

Is the new boiler's water level lower than the old one?  If so, you might want to look at the wet returns and see if you inadvertantly turned a wet return into a steam main.  This could be the source of the hammer. 

Also, did you install a new setback thermostat?  Is a setback and recovery a new part of the picture?  As mentioned by earlier replies, this could be the source of the problem.

Joe V_2

There is one test you

can try.  Ask the owners to leave the boiler off until you get there in the evening the turn up the thermostat ten degrees higher than actual and see if it hammers and you might be able to tell where the hammer occurs and you might see what the problem is. 

If it is hidden in floors,  you can then ask owner to reduce set back.

TomM

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Since you say that the main vents were not changed in 25 years, and you changed all the radiator vents, perhaps steam was not getting to a certain area, but now is getting to that area causing a hammer. 

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Maybe the hammer was there before, but the vents were not working properly, so they never heard a hammer because there was no steam. 

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