Cast iron baseboard keeps busting

Oldironside

The house was built in 1957 and we had a new gas furnace put in 2013.  We were able to heat all three zones and get them going good.  Fast forward to 2020, we could only heat up one zone at a time and it wouldn’t get above 70.  Right after this started we had two baseboards give out.  Loud pop and water coming out of the cast iron baseboard.  We had those broken ones replaced and everything was good for a week— the zones all heated up properly.  Now, today the heat went back to a zone at a time and I just had another old baseboard on a different zone bust.   Is this just old age or is air getting into the system and causing this?   Not a lot of plumbers will touch this stuff or know much about it.  Any help would be appreciated on where I can look to see what’s causing this, if anything.  

EdTheHeaterMan

Cast iron breaking is unusual at the designed operating pressure >30PSI. The only other thing I can think of is Freezing will crack cast iron. When the ice thaws the water in the system will find that leak and flow until the water is turned off.

How cold do the other zones get when you are heating only one at a time?

I did have a crazy problem with a hydronic coil system. After several years of operating just fine, one of the U bends on the coil burst, I replaced the coil and in 6 months the coil burst again. I replaced the coil again and added a 30 PSI relief valve close to the coil. Another U bend burst and I was at a loss to explain the cause. Then I looked at the new boiler I had installed a little closer. I used a 007 circulator on the system loop when I should have used a more powerful pump. The new boiler was one of the first ModCon boilers I installed. After the larger pump was installed the coil bursting problem went away.

The only thing I could think of is that the water in the coil was very hot. If the circulator was not putting the water thru the heat exchanger fast enough there would be a build up of enough heat in the coil then it would flash into steam and that powerful rapid expansion was happening close enough the the coil that cause the U bend to burst.

Can you post some pictures of your boiler and the near boiler piping from floor to ceiling with at least 3 different vantage points. Include close ups of any circulator pumps or zone valves you have operating those zones. You may have an unusually incorrect near boiler piping situation or a wrong circulator situation like my coil bursting customer.

HVACNUT

Lots of drafts?
Is it below freezing when this happens?
Do you setback the thermostats?
If the thermostats are set low so the water doesn't frequently circulate and freezing air is getting in somewhere, then cast iron will split like a banana. 
It's either that or you got the batch of baseboard that spontaneously explodes for no reason. 

kcopp

Something isnt adding up... What was installed for a boiler?
Did they do any additional piping/ re work of piping? in the basement when that was installed?
Where is this that not many contractors wont work on them?
CI baseboard heat is a really nice set up...

EBEBRATT-Ed

What temp is the water running at and what is the boiler pressure. The CI baseboard should last forever

pecmsg

Where are you?

Pictures of the boiler and bad radiators would help.

Oldironside

There’s no way it is freezing.  It’s just not that cold and it’s an Interior wall. 

The only thing that changed recently before the first burst is we had the water tank replaced. I’m thinking maybe the pressure in the boiler is up and the relief value isn’t working properly and the old cast iron baseboard is the weakest link in the chain so it burst there.  It didn’t burst on a seam it just burst on the face of it mid 2 foot section. 

 I’ll send pics when I can the furnace and indirect boiler are Weil Mclain.  This setup worked for 8 years before we had these bursting issues and like most of you I thought cast iron was pretty much good to go for a very long time.  

Thanks for the replies.  

Btw when I said it was hard to get someone to come replace cast iron baseboard I wasn’t exaggerating.  I called 50 plumbers and had a few come over only to ghost me.  I had to get a friend of the family and pay for him to come down from another state to replace my first two busted ones.  Now as of last night I have two more.  

EdTheHeaterMan

You need to think like WATER.... If you were H2O what would you do? at 32°F you would become solid and at 212°F you would become a gas. But that is at atmospheric pressure at sea level. What if you were at a different pressure? For the most part, the pressure in a closed heating system the boiling point of water is much higher than 212°. But what if the water was around 200° and for some reason the pressure dropped below Atmospheric pressure (A Slight Vacuum). When a circulator pump comes on the inlet of the pump has to be lower that the outlet pressure. Depending on the location of the pump, the expansion tank (PONPC) and the radiator, is it possible that the water pressure mignt drop low enough to cause the 200° water in a radiator to spontainously expand into steam?

That would increase the volume of the closed system by 1700 times its original volume of only water. TNT only expands 960 times its size before exploding. and they use that stuff to move mountains in order to make roadways and train rail ways. That might explain the force needed to bust out a section of cast iron. That is why I would like to see the boiler and the type of pumps and the near boiler piping. Remember the Coil bursting problem I had? It was fixed by using the proper circulator. If I had read the instructions better when I first installed the boiler, the coil would never have burst the way it did. I still can't visualize how the burst location was the weakest link in the system. even installing a relief valve very close to the burst location didn't remedy the problem. But getting the water flow to the proper designed parameters solved the problem. 14 years later, and that coil has not failed.

mattmia2

The water isnt suddenly going to find more energy when the pressure drops. It will vaporize until it brings the pressure back up. It will flash in to steam but still at low pressure. I think those little bubbles of steam can erode the surface.

Is your system getting a lot of makeup water? Constantly getting fresh water with oxygen in it or using non barrier plastic tubing will let oxygen in and rust the cast iron quickly.

Mad Dog_2

All I can tell you is this.  3 years ago we installed Competitive Cast Iron Baseboard (A real no no for me) because the vendor SCREWED UP and failed to order USA made.  He was stuck w them so we chanced it.  4 years later, 80% of it has been ripped out and replaced...cracks  Sandhills, bad milling on faces.  This year we out in 4 more sections of USA brand.  1 out of 5 leaked.  The Supply we use said ALL THE CIBB is NOT up to snuff   sad  I love how sleek and rugged it is....boy do I miss Slant Fin!  Mad Dog 🐕 

EdTheHeaterMan

mattmia2 said:

The water isnt suddenly going to find more energy when the pressure drops. It will vaporize until it brings the pressure back up. It will flash in to steam but still at low pressure. I think those little bubbles of steam can erode the surface.
.

I might have to disagree unless you can explain this.



This happened to 3 different coils within 2 years. It started 3 years after the new boiler was installed.
My only explanation is that there is a micro explosion of water to steam right near the burst. And I understand that these happen in steam boilers in many cases. sometimes this banging sound is enough to rattle the building. I don't think that the entire volume of the boiler flashes to steam. I just believe that there is enough of it to burst the U Bend before it has a chance to dicipate into the system and cause relief valve to operate and release the pressure.

But you may have a different theory mattmia2. I am willing to listen to your thought process and get a new understanding into how this can happen.

hot_rod

In a residential steam boiler, how much does pressure increase when it crosses from water to steam?

Jamie Hall

Keeping in mind that there are only three ways that the cracking could happen -- faulty casting (unlikely after so many years), freezing (said to be unlikely), or overpressure I kind of lean towards overpressure. And it could be momentary flashing. Not that the steam from the flash could do it -- as noted, it wouldn't flash system wide -- but it would be the shock waver from the water collapsing back into the steam bubble -- the same then that causes cavitation damage in pumps and ship propellors. But how you get to that point -- haven't a clue.

JUGHNE

I had a customer with CI old school rads. He had a constant drip on a lower nipple.

Someone changed his fill valve which would have involved draining the entire system.

Then the upper rads would not heat, the guy then bled those rads to get heat.
Then the pop off valve would drip, the guy fixed that with a pipe plug.

His expansion tank had been water logged with no room for expanding water causing the pop off and the rad to drip. The pop off was changed and all was good as the upper rads had air for compression.

I ended up changing the boiler for other reasons and adding an oversize expansion tank.

The pop off and CI raid both stopped dripping.

Is there a chance the house could have seen a freeze up in the past that you may not be aware of?

Could have weaken some of the cast without breaking and then failed expansion tank have done them in?

EdTheHeaterMan

Back in the day, I gave a price to a gentleman in Stone Harbor NJ to upgrade his old oil fired, coal converted boiler with a new Carlin oil burner that would be mounted in the fire door. The job would have included filling in the ash pit with sand and vermiculite insulation with a cap of fire brick. It would also include new controls and a new circulator pump, water feed , expansion tank and relief valve, new vent connector pipe and barometric draft control. I called this a Complete Modernization. He failed to do the job.

6 months later I got a call from him to come out and fix the heater because he had no heat. I arrived to find that the relief valve may have been leaking so some genius repaired that leaking relief valve with a 3/4" pipe plug. I also found the side of the cast iron boiler was completely missing. There was a 1.5 ft square section of cast iron that blew thru the sheet metal jacket and put a 2" dent in the block wall that the boiler was next to. So I acquired a great respect for water and hydraulic pressure that day.

I told the customer that I could no longer offer him the complete modernization anymore, the boiler would need to be replaced.

The fire department calls that a BLEVE. Boiling Liquid Expanding Vapor Explosion. Lots more fun when the liquid is flammable, like Propane

hot_rod

We had a bunch of exploded zone valves returned a few years back. Brand new high rise building, flooded many units below. It was in fact a freeze inside brand new condos, zone valves were inside the fin tube enclosures.

Cavitation can be destructive, but usually more of and erosion looking failure.

My first thought is freezing, both the heaters and that coil.