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gas furnace

I recently had a gas furnace installed. The house has water-filled radiators. When the furace is running a loud percolating/boiling sound comes from the area of the expansion tank. I've had the installer back and he doesn't have a satisfactory answer. Any ideas ?

Re: gas furnace

You have a BOILER there, not a furnace.

The symptom you describe could be caused by any one of several things.

I assume you're talking about one of the newer style expansion tanks that look like a 20# propane fuel tank you see on barbeque grilles.

In any event, since the boiler was recently installed, the work should be guaranteed by the installer for several months.

1) Check the water temperature on the boiler gauge; it should read 160-180 degrees; if it's 200 or higher it could be causing some slight boiling.

2) the expansion tank may have a slight internal leak in its neophrene bladder (the expansion tank is 1/2 filled with air & 1/2 filled with water under 12 lbs of pressure); leaks and bladder failure, even in new tanks is common.

3) there is unvented air inside the piping that is causing the noise; there is usually an air seperator device directly above the expansion tank that should be working.

Keep after the contractor & call them back regularly until they come over & find the cause.

They are probably waiting for the marginal part to fail, so they can replace it (should be free of charge).

Re: gas furnace

The expansion tank is not new. It's cylindrical shaped and could be 20 lb? but it is definitely old. I think your # 3 idea is probably the problem. The expansion tank was not replaced with the boiler. There does not seem to be room above the old tank for an air seperator device? it's smack dab up against the basement ceiling. Do you think i need to have new tank installed?

Re: gas furnace


What you are describing is the older style oblong, steel expansion tank, usually green (see photo at site below).

There is usually a copper pipe coming out of the boiler or from an "air scoop" that goes directly to one end of the tank & has a shutoff valve between the boiler & the tank?

These older tanks usually work ok but they are more likely to get "waterlogged" (lose their air charge), & fill completely with water.

They have to be completely drained and re-charged with air once this happens.

Could you check the boiler gauge and report what the psi (water pressure) gauge is reading now?? Does the psi needle go up to near 30 psi when the boiler gets hot??

There are two needles on your gauge; one points to the water temperature, the other (usually black) points to the water pressure in psi (should be 12 to 20 psi).

When there are problems with your type of expansion tank the psi needle usually reads high---up to 30; when it goes over 30 psi, the PRESSURE RELIEF VALVE opens & spills a small amount of water on the basement floor as a safety measure to prevent excess pressure buildup in the boiler; if this happens, simply place a pail to catch the water.

Then again, you may just have an internal fitting air leak inside the expansion tank.

Can you see any water at all leaking from the fittings at the expansion tank??

The site below has some pictures of some of these components & valves:
Click onto "homeowner", then scroll down & click onto "valves" then onto "ASME relief valve"; the one pictured on the right is more common.

Then scroll down and click onto "tanks" and click onto "compression tanks" to view a photo (your tank may look slightly different); then click onto "tutorial" to view diagrams of how these tanks are piped.

Their job is to temporarily absorb a gallon or two of hot water when the boiler heats up (water always expands 5% when heated).

Next, scroll down to "diaphragm tanks"; these are the newer tanks that everyone puts in these days; they cost only $35 plus installation & are usually much less trouble than the older steel tanks.

Please post back.


Re: gas furnace

let me check all that out and get back to you
appreciate your detailed assist
i have to print out and go through the sequences you gave me

Re: gas furnace

i did look at the tank on the site you gave and my tank is obviously much older
it is concave at both ends
unfortunately i don't have internet at home so i respond to you from work and then return home with your notes/suggestions and respond asap
thank you for your patience

Re: gas furnace


Yep, concave ends---that's the traditional oblong, steel tank very widely used in HW heating systems; it functions EXACTLY like the one pictured in the Bell-Gossett site.

Re: gas furnace

jack thank you for your patience
i think i found the critical info in the boiler manual for the installer
"closed-type_ welded gas tight and located above boiler. tank is partially filled with water, leaving an air cushion for expansion."
* Make sure this type of tank is fitted with a tank fitting, such as the B&G Tank-Trol or Taco Taco-Trol. This fitting reduces gravity circulation of air-saturated tank water back to the system and prevents the air from bubbling up through the water as it returns from the system. "

i'm not sure this is on the system but i think not
as soon as i get to the bottom of it i'll let you know how i made out

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