Makeup water causing boiler failure due to thermal shock

If it causes a problem I think it is likely to be something that warps and leaks later and won't be something you can definitively tie to the thermal shock. Usually the feed is relatively slow compared to the volume of the boiler so the temp change isn't that fast unless the boiler was almost empty.

In theory it's impossible.

A tiny fresh water feed pipe feds the bottom of the boiler pipe mixing with very hot water inside. The cold water doesn't stand much chance.

Not in the 50+ years I have been in the business. I think there is still time, hopefully to look.

engine blocks usually warp and you get head gasket failures soon after.

my understanding is that about the only way that bmw inline 6's die is if the cooling system fails and you go with some option other than towing it/fixing it by the side of the road and the compromised cooling system causes the giant aluminum block to warp then you have head gasket problems.

this happened wile i was typing. I'm not sure if people have narrowed down if it is the overheating or the trying to fix the overheating by adding water(or trying to continue to drive it with a leaking cooling system after you've added water). I think it can be both but your best bet is to be patient and let it cool down before adding water.

I have seen a boiler crack form operating it than opening the water feed valve. The time it happened was not "Normal Operation" though. it was being dry fired when I arrived and I told the customer to shut off the switch. After they shut off the switch, they asked my why it was not heating the radiators, I told them the home was winterized and the boiler water was drained. There was no water in the system.

With that and before I could stop them the cold water feed was opened and Pop… Fizzz…. the boiler cracked then and there. Not covered under the warranty. The boiler needed to be replaced.

This was in a summer home that has a Weil McLain WGO-3 and the kids came down for spring break without the parents knowledge. That is, until the parents needed a new boiler.

Under normal conditions a boiler "at operating temperature" will not fail from thermal shock when adding makeup water. Unless the installer piped the makeup water in some stupid location. (Never say Never)

There was no question about the dry firing Paul, As soon as the WM rep looked at the front door opening, the warranty was voided. I still needed to try though. 

Another boiler (a steamer) I installed in a church dry fired as a result of a run away gas valve. The clocks in the church were all stopped at 10:48 (PM) and I got a call at 2:00PM from the fire chief of Cape May. (the West Cape May fire chief was also the fuel oil dealer for the church and he was on scene.) I arrived at 2:45 to see a half dozen fire and police vehicles on scene and steam still blowing out of the boiler room door.

The best guess was that the electrical event that caused the clocks to stop must have been some type of surge that happened while the dual fuel burner was operating on natural gas. The gas velvet must have stuck open as a result of the surge.  With all the electrical out and the gas valve stuck open. The flame kept going thru the burner even though there was no electricity to operate the combustion blower …Or the boiler feed pump.  Eventually the boiler water line dropped below the minimum and the boiler cracked.  Steam was pouring out of the boiler room chimney combustion air openings and a window that was left open for some reason.  The gas continued to burn inside the boiler until the fire department shut off the gas at the gas meter.  

I was called just to tell everyone the boiler was safe to keep shut down and after I turned off the gas to the boiler, I could relight all the pilots of the rest of the appliances in the building.  Hartford Boiler Insurance paid for the replacement boiler and most of the labor.  Got her back up and running within 5 days.  They scrapped the dual fuel burner with the replacement boiler. Gas only this time.  “Oil Company not happy”

the coating usually flakes off my cast iron when i do stuff like that.

That's an odd statement.

True,

But I find it odd because IF it was a forced air system instead, it wouldn't have mattered at all.
There's a ton of IF's, like the classic "if your aunt had…….." joke.

That's all.

So cut to the chase - @ethicalpaul are you suggesting that damage to a boiler due to thermal shock is just an unfounded myth?

In my house there is a scenario that seems could lead to thermal shock:

• Zone1 calls for heat and the boiler water gets up to say 150. This is a small zone for just the family room with baseboard radiators.
• Zone2 calls for heat and introduces water into the boiler at say 65 (due to nightly setback). This is a large zone with lots of water and many floor standing radiators.
• Water temperature in boiler rapidly drops to 65, while cast iron jacket remains initially at 150, causing metal to rapidly drop in temperature - thermal shock or stress.
  Is that a bad thing, or can the boiler handle it?
• In my case I initially installed a system bypass, then later re-piped to use a thermostatic mixing valve, not just for thermal stress, but also to avoid condensation from low temperature return water.

Thoughts?
Eric Peterson

Same

The part above the water line in a steam boiler could be and likely is significantly above ~212 f since it won't be able to transfer heat to the steam gas nearly as efficiently as it can transfer to the liquid water. I wonder is surging and thermal shock and maybe particularly not resistant to thermal shock construction is how the problematic burnahms run in to problems.

My brain just thawed out so now I remember when H B Smith series 28 sections would crack on hot water systems when they would switch from night set back to day time temps. This was before they added a pump that would pump water from the discharge to the boiler's inlet to temper the water. (this was similar to a primary/secondary loop set up) The company I worked for would usually add a 2" B&G pump to do the pumping' They originally tried using a series 100 B&G pump but they would not flow enough water. A few years later it became part of the boiler's specs and every other mfg that made similar boilers followed suit.

Those are big boilers in big buildings. think the size of a medium size shed.