Runaway Boiler

Alan(CaliforniaRadiant)Forbes

This was on a job we did two years ago.

Weil-McLain AHE boiler serving radiators, each radiator piped off a manifold.

Operating limit at 180° with a manual reset high limit. The owners called me up one morning and said they heard three explosions in the basement. Went down to investigate and the room was filled with steam.

It took me a long time to start using PEX for primary piping because I always worried about this happening. A simple aquastat could have prevented this.

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Weezbo

that looks knarly....

that is from over temp and pressure..so no control over water temps and no low water ...well there is a case for much lower water temps if i have ever seen one

Steamhead

Very bad

I think I'll stick with copper. It should hold more pressure than it takes to open the safety valve.

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Unknown

Hmmmmm

Even a water heater relief valve opens above 200° F. No help there. Water heaters on radiant are even more scary, for many reasons. What temperature is 30 PSI water when it turns to steam under pressure? Tubing would be long gone before that temperature is reached. Without a back-up limit control, that system has a different backup temperature control: the tubing melts....

Sure hope he has a Low Water Cut Off on that system.

Wouldn't save the tubing, but it would shut off the boiler before it set anything on fire. Do gas water heaters come with LWCO's? If not, how do you connect one? It's bad enough that they have no spill switches OR rollout protection. Sure will test the CO detectors, if anything fails. Hope they are sensetive.

Some systems are one simple failure away from disaster.

EVERYTHING eventually fails. Hope the back-up control catches it when something fails.

What's protecting YOUR tubing???

Noel

Weezbo

new thought....

perhaps, there maybe some value in having a piece of pex in "somewhat' near boiler piping....as it would be a first point of failure in the event other safetys dont respond inadequately for some reason. ....maybe Alan, this may be a cloud with a silver lining for you..and there could be a whole section of new codes written to govern the application of the newly invented "Forbes Control Loop" *~/:) i like the idea .i think on this a bit and send you a picture with one i will designe into my next boiler cool?

EJW

Notice something?

The cinch clamp joint held. EJW

bob_44

Rating

Alan, I don't get it, if you have an operating control at 180 plus a manual reset high limit how did it run away which control failed? Pex is rated at 100psi at 180F and 80 psi at 200F. Why did it blow? bob

Alan(CaliforniaRadiant)Forbes

Well,

the only thing I can image is the the operating limit and high limit failed, allowing the boiler to run away:

180°.....190°.....200°.....210°.....220°

at which point the tubing melts before the relief valve opens, allowing the tubing failure to become the relief valve.

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Mark Eatherton1

Makes one wonder...

what might have happened if the PEX hand't been there eh...

I had a situation once I'll never forget. I had found a piece of 3/4" PEX being used in a system I'd installed that had gotten kinked by the rentawino the boss had hired for the day. I found it as I was walking off the job on a Friday afternoon. In my haste to rectify the situmacation, I grabbed a torch to heat up the kink and get it out. One slight problem. I forgot the system was under a 100 pound test. I no sooner got the tubing to the clear stage when all of a sudden it started expanding like a BALLOON. I yelled "AWWW S#!t" and dove off the 5 gallon ladder I was using only to hear this gawd awful explosion just as I hit the ground. Sounded like a 1/4 stick of dynamite going off.

The carpenter working on the second floor must have jumped from one floor to the next without touching any stairs, because he was IMMEDIATELY standing at the top of the stairs, asking me if I was OK.. I emberrassedly told him I was fine, and went to my truck to get the necessary items for a quick splice job, new underwear and an air compressor.

So much for getting off early...

ME

Constantin

Like Dan said,

"You can't make this stuff up". I am glad you came out OK!

As for the melted PEX, yet another reason I required my installer to put in a LWCO even though he insisted no LWCO was required. You can't be too careful with fire, pressure vessels, and water.

clammy

Manual hi limit

When ever i run into pex or rubber tubing mostly pex for home runs or main feeds i install a manual hi limit it seems to almostly always stop these things from happening espically runaway limt controls but i am very paranoid when it comes to plastics being exposed to high temp 180 you will always find a manual hi limit on the jobs i do espically if the radiant or electronic reset controls just a habit i got into years ago some body told me once and it stuck peace clammy

Steve_35

> Even a water heater relief valve opens above 200°

> F. No help there. Water heaters on radiant are

> even more scary, for many reasons. What

> temperature is 30 PSI water when it turns to

> steam under pressure? Tubing would be long gone

> before that temperature is reached. Without a

> back-up limit control, that system has a

> different backup temperature control: the tubing

> melts....

>

> Sure hope he has a Low Water Cut Off

> on that system.

>

> Wouldn't save the tubing, but

> it would shut off the boiler before it set

> anything on fire. Do gas water heaters come with

> LWCO's? If not, how do you connect one? It's bad

> enough that they have no spill switches OR

> rollout protection. Sure will test the CO

> detectors, if anything fails. Hope they are

> sensetive.

>

> Some systems are one simple failure

> away from disaster.

>

> EVERYTHING eventually

> fails. Hope the back-up control catches it when

> something fails.

>

> What's protecting YOUR

> tubing???

>

> Noel

Steve_35

LWCO on a gas WH

> anything on fire. Do gas water heaters come with

> LWCO's? If not, how do you connect one? It's bad

> enough that they have no spill switches OR

> rollout protection. Sure will test the CO

> detectors, if anything fails. Hope they are

> sensetive.


You can use a Field thermocouple adapter. This is the one that comes in a kit to allow you to connect a gas water heater to a power vent. Use a RB-122 and connect the thermocouple adapter to the LWCO with 12ga wire. I've got a set up like this in my shop with a sealed combustion LP WH.

Unknown

Something to keep

on your mind when adding switches and controls to the thermocouple millivolt circuit. That 25 to 35 millivolts can only handle so much especially today with FVIR on water heaters. The 12 gauge wire would give you a lower millivolt drop however.

The water heater has an ECO built in as a safety to shut the water heater off on high temp (195 degrees). When I was with the gas company we actually fired a heater with low water and the ECO shut the unit down after 5 minutes running time with 10 gallons of water in a 30 gallon tank. The pressure was at 27 pounds and the temperature of the water was 192 degrees when the ECO opened and shut off the millivolts to the pilot safety and shut down the water heater.

I am not sure if that is something water heater manufacturers test and I do not know if an ECO can be called a low water protection device.