Boiler section seals and air leak test

Camdo

I have a Thermoflo OWB-3-T-S2 boiler made in 2017 (5 years old), that was never used because it leaked. I disassembled the boiler sections and found the upper tie rods were improperly torqued at 5 lb-ft and the bottom at 40 lb-ft. I torqued the rods properly and the leaks disappeared except for a lazy drip from the bottom seal. I decided to disassemble the sections since they were in pristine condition. I found the sections to be in excellent condition and saw no apparent cause for seal failure other than incorrect tie rod torque. The glass rope remained intact bonded its section and without tears. There is no scale or rust on the mating surfaces.

Thermoflo section repair kit 386-700-852WT includes 2 seals and glass rope and adhesives costs $160. Weil-McClain sells a seal kit for their WGO boiler with almost the same part number 386-700-852 which leads me to believe the seals are the same. But better yet Weil-McLain sells seals only (no glass rope) 592-800-010 for $12. Does anyone know if the Thermoflo and Weil-McLain seals are the same?

When I bolt the sections back together, I will do a hydrostatic pressure test (18 psig) to test for water leaks. I would also like to test the glass rope seals for combustion chamber air leaks. I am not sure how to do that, or even if it is necessary. Does anyone have suggestions?

EBEBRATT-Ed

I dont think there is a practical way to check the fire side. I suppose you could connect the flue and make a temporary blast gate to block the flue (remover it afterwards of course) and use a smoke candle in the boiler. You would have to block the burner opening. normally those are not tested

The seals between the sections will probably seal up.

I don't know about the compatibility of the gaskets with Weil McLain

Camdo

Thank you for you comment @EBEBRATT-Ed
"The seals between the sections will probably seal up"

Were you referring to the glass rope seals between the sections?

I am wondering how important the rope seals are, since there should be negative draft at all times in the combustion chamber. My experience with hot air furnaces is that a slight crack in the combustion chamber is all it takes to be breathing unacceptable exhaust fumes in the house. Would a boiler be any different?

I am also wondering if the glass rope is intended to resist any pressure differential across it. It seems to be very porous. Maybe its intent is to impede flow rather than act as an impermeable gasket.

I like the smoke candle idea. I could cap the vent connection and burner opening (gun removed) throw in a smoke candle and close the door. If the caps were made of rags, there would not be any pressure build up. On the other hand maybe there should be some pressure build up for a valid test. Correct lighting will be critical.

EBEBRATT-Ed

The glass rope seals the combustion gasses inside the boiler. If installed right they work fine.

I was talking about the boiler seals they sometimes take a bit to seal

Jamie Hall

Two minor thoughts here. First, a part number which is "almost the same" doesn't mean the part is the same -- or even almost the same. At least in the automotive business... The second point is that at least some of the seals Weil-McClain uses have very very specific dimensions, and are picky both about dimension and installation.

Camdo

EBEBRATT-Ed said:

I was talking about the boiler seals they sometimes take a bit to seal

I was wondering if that lazy leak would seal itself in time. One drip per 10 minutes was about the rate. Too late now though, I took the sections apart, since the parts were so new and it being springtime, I would never have a better opportunity.

It has crossed my mind to put a little high temperature rtv on the elastomer seals to give that little extra squeeze to make the seal. The seals appear to be in excellent condition like the rest of the boiler. They were almost flush with the face of their retaining groove, and the mating surface is just a flat face, so there was very little crush action. Perhaps the seals had taken a set, or maybe this is the intended design.

How hot can the cast iron get, since it is next to water. High temp RTV (500 F) may work just fine.

EBEBRATT-Ed

NO @Camdo don't put any type of sealer unless the boiler mfg calls for it. Once it runs it may seal up

Jamie Hall

I'm a little worried about the comment "just almost flush". Have these seal rings been used once already? I've had dismal luck with reusing o-rings, and those seals are, if memory serves, a variety of o-ring. They tend to take a set when first installed, and may not reseal properly. I'd use new...

Camdo

I agree @Jamie Hall new is the only way I will go. I was surprised the seals did not stand proud when the sections were separated. Maybe the design calls for very little crush, or maybe they have lost their elasticity. The boiler is only 5 years old and hardly used. Maybe lack of water made them less resilient. They appear to be some type of elastomer but not like an o-ring buna or neoprene. Both are rectangular in cross section and approximately 3 and 6 inches diameter. Tomorrow I should have the Weil-McLain versions and see if they are the same as Thermoflo.

Jamie Hall

Ah those blessed rectangular ones. Make sure they aren't twisted when you pull the sections together. Been there, done that, didn't work...

mattmia2

Maybe it is a synthetic rubber-fiber composite