Radiators hissing in the middle of the summer

Steve_123 · August 2007

for your quick and helpful replies.

Steve_123 · August 2007

Hissing raditors

Hello all I need some help.

Today we started noticing that our radiators were hissing like the heat was on. It happend at least 4 times so far today and it was about 15-20 mins in between. The thermostat is set at 65 and it's at least 75 in the house. The boiler isn't on as the pressure is at bare minimum and the pipes leaving the boiler are cold.
What could be causing this hissing?

Thanks,
Steve

Steamhead (in transit) · August 2007

What type of system?

Steam or hot-water?

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Steve_123 · August 2007

Steam and by the way I tried draining some water out of the system. I noticed the site glass was about 3/4 full so I drained it to about 1/2. After doing so I have only noticed the hissing once.

Steamhead (in transit) · August 2007

Something is generating a bit of pressure

Maybe the fill valve opened? Do you see any pipe leaks anywhere?

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Steve_123 · August 2007

Hmm no leaks that I know of. I have been running a dehumidifier in my basement most of the past couple months. I have a automatic fill regulator (not sure what to call it) that automatically adds water when it's needed. I thought that maybe due to the dehumidifier that it was adding water, but we haven't noticed this until today. Anyway, that's why I decided to empty some water.
Any thoughts?

Steamhead (in transit) · August 2007

Watch the water level

and see if it rises again. Sometimes water-hammer from a faucet or solenoid valve (washing machine, dishwasher) can lift the fill valve.

Also, does your system have any vacuum-type vents (including main vents) on it?

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Steve_123 · August 2007

I don't believe my radiator vents are vacuum vents. They are the ones that the float closes the vent when steam enters the vent. I don't know what type my main vents are. Sorry.

Steamhead (in transit) · August 2007

If you can tell me

what make and model the vents are, I'd know if they're vacuum vents.

If there are some vacuum vents on the system, they may cause the remaining non-vac vents to hiss if the pressure falls a bit.

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Steve_123 · August 2007

The main steam vent valve is Hoffman No-75 (hard to read the imprint but I think that's what it said).

All my radiator vents are Hoffman No-1A
The No has a superscript "o" on both

Steamhead (in transit) · August 2007

Then

they are not vacuum vents.

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Steve_123 · August 2007

So..

Do you think it was still due to the added water in the system?

bill_71 · August 2007

do you have a tankless coil for your domestic hw in your steam boiler? aquastat could be screwy and heating the boiler up to make just enough steam to get things to hiss every once in awhile...or someone could have turned it up to 220 or so
edit*......nevermind, this would also make the near boiler piping a bit on the warm side( i missed that part of you post)

Steve_123 · August 2007

Hot water

No I have a separate hot water heater. Is that what you mean?

Steamhead (in transit) · August 2007

That's

the only thing I can think of now.... keep an eye on it.

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Radiators hissing in the middle of the summer

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