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Help Identify Furnace Boiler Popping Sound

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  • Jan 14th, 2022 1:04 pm
[OP]
Newbie
Nov 5, 2015
14 posts
East York, ON

Help Identify Furnace Boiler Popping Sound

Looking for some ideas about the source of a short-lived popcorn-like popping sound from my furnace / boiler.

Popping occurs within 10 - 15 seconds after furnace ignites (one to several popcorn-like gentle pops, but NOT banging or rambling or anything like that). I can only hear these few pops when I'm in the basement (where the furnace is located) and not elsewhere in the house. There is not detectable vibration on the furnace or the vent pipe during popping.

The furnace is a natural gas-powered Raypak 134WT (Raytherm), installed in 1986. Other than the popping it works perfectly. I think I first noticed the popping after I replaced a Armstrong S25 circulator (B&G 100 equivalent) with a Taco 007 circ, about three years ago, but maybe it was popping before I just didn't notice. No other modifications made.

More bout the furnace: The burners are clean, the fins are clean, and the air is purged from radiators. Pilot light has a nice blue flame, and burners ignite immediately (no delay from clogging). Chimney liner is clean, and not blocked. Pressure in the system is a steady 12PSI. Temperature control on the boiler is set at 160F. Home thermostat is set at 19C / 66F.

Anything I can do to help diagnose the cause of this popping, and stop it if possible?
5 replies
Deal Addict
Jan 1, 2007
1261 posts
252 upvotes
This is a boiler, not a furnace right?

Your problem is probably insufficient water flow through the boiler chamber causing micro-boiling inside the tubes. Get a stronger/better pump. A constant flow pump. I had something similar years ago.
Jr. Member
Sep 12, 2017
192 posts
133 upvotes
Does the circulator start as soon as the thermostat calls for heat? Or is there a delay. If it delays start there may be boiling occurring causing the popping.

However at 12psi the boil point should be pretty high. Are you sure the pressure gauge is correct? Maybe check at a bleed valve at the highest point to see if it really is well pressurized.

CHM
[OP]
Newbie
Nov 5, 2015
14 posts
East York, ON
CanadianHandyman wrote: Does the circulator start as soon as the thermostat calls for heat? Or is there a delay. If it delays start there may be boiling occurring causing the popping.

However at 12psi the boil point should be pretty high. Are you sure the pressure gauge is correct? Maybe check at a bleed valve at the highest point to see if it really is well pressurized.

CHM
Sorry if I wasn't clear, it is a gas furnace. The Taco 007 circulator runs continuously , and the burners light up immediately when called for.
I thought may be some debris got into the pipes in the furnace, so flushed it thoroughly last night, but it did not help. Still hearing 3-5 little pops within 10-15 seconds of the burners lighting. I bled the system, too. Everything is working, except for the concerning little pops, although it's been popping at least 2 winter seasons, to no detriment, just concern.
Deal Addict
May 21, 2015
1184 posts
777 upvotes
Sarnia, ON
It sounds to me like it may just be some metal expansion somewhere. I wouldn't worry about it. As for the circulator pump we have an Armstrong so I can't speak for the Taco model you replaced yours with. Just make sure that if it requires occasional oiling, like my armstrong does, that you follow up on that. BTW our boiler is 63 years old and still working fine.
Bujnik wrote: Sorry if I wasn't clear, it is a gas furnace. The Taco 007 circulator runs continuously , and the burners light up immediately when called for.
I thought may be some debris got into the pipes in the furnace, so flushed it thoroughly last night, but it did not help. Still hearing 3-5 little pops within 10-15 seconds of the burners lighting. I bled the system, too. Everything is working, except for the concerning little pops, although it's been popping at least 2 winter seasons, to no detriment, just concern.
[OP]
Newbie
Nov 5, 2015
14 posts
East York, ON
Beneful1 wrote: It sounds to me like it may just be some metal expansion somewhere. I wouldn't worry about it. As for the circulator pump we have an Armstrong so I can't speak for the Taco model you replaced yours with. Just make sure that if it requires occasional oiling, like my armstrong does, that you follow up on that. BTW our boiler is 63 years old and still working fine.
Yes, it sounds exactly like metal expansion pops, but I'm thinking it should also sound after furnace burners stop and metal cools...
Ps: I can't see why changing circulators would have "caused" the popping, but I'm referencing it anyway as the only change made to the system, and timewise possibly when the popping started.
Ps2: Neither my previous armstrong nor the new taco pump requires oiling.
The furnace is 35-36 years running, and I hope it lasts as long as yours, it's a great machine, easy to maintain, with no microchips and motherboards.

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