Low water cut off malfuntions

tonylap

: I have a three year old low pressure steam boiler that the heat exchanger just cracked. I was told that it had dry fired. I am in NJ, it is in an old small commercial building 3 stories about 3500 sf. The state requires 2 low water cut off controls. The new boiler was installed because the old boiler cracked, it was about 22 years old. In discussions with 2 heating installers they both think that the sediment in the piping system caused the low water cut off to clog with wet sediment that gave a false reading of the water level in the boiler telling it that the water level was OK when it actually was not. The boiler then dry fired cracking the heat exchanger. The original installer of the newer boiler told me that that could not happen if it had only the one low water level cut off that the boiler was originally designed for. It occurs to me that the last boiler cracked after the state inspector required the installation of the second low water cut off. Any one ever heard of such occurances

BobC

A picture of the LWCO mountings to the boiler would help us see whats going on.

Jamie Hall

Float type low water cutoffs must be blown down and checked regularly to ensure they are functioning. Not only gets rid of the crud that builds up in the float chamber, but checks that the switch actually opens. Probe types also need to be checked regularly -- at least in my opinion -- by deliberately lowering the water level and making sure that they do, in fact, cut off. They may need to be cleaned.

This is not optional maintenance.

Did dry firing cause the cracking? It certainly could have -- but there are other possibilities, too.

EBEBRATT-Ed

@Jamie Hall said"This is not optional maintenance."

Unfortunately steam systems (all heating systems really) require maintenance to work safely and to have any reliability and longevity. Failure to do this results in major problems. Just like a car. Cars won't run long without oil, boilers need water. Low water cutoffs need at the least yearly maintenance

tonylap

Thanks for the input. the locations of the low water cut offs were as per Weil McClain recommendations. The low water cut offs are probe type. They had been serviced twice over the month because of malfunctions before the crack event. The diagnosis of dry fire was postmortem. The building smoke alarms went off, I had my maintenance man turn off the emergency switch to the boiler at once. It was too late, damage was done. A week earlier a similar thing happened. Smoke alarms went off the electronic control board in the boiler fried and the system shut down. At that time the service tech found that the low water cut offs were again full of sludge it was cleaned up, the electronic board was replaced and the system was up and running. He had done a full seasonal maintenance about 3 weeks earlier which included clearing sludge from the 2 low water cut offs. The system had its yearly inspection by the State inspector 5 days before the final breakdown. His inspection was limited to checking if the safety mechanisms were installed, wired and operating correctly. The inspector tested the system with the jacket off but did not remove any parts. The inspector found all that devices were installed properly and in proper working order.

tonylap

What are other possibilities for the crack? Can the probe low water cut offs misread if sludge is present?

KC_Jones

Your comments are a bit confusing to me. If you have probe type they are installed in the block (one of them anyway) and shouldn't need the sludge cleaned out, for that to happen the whole boiler would have to be filled with sludge. If a low water is filling with sludge it's a float type and you should be blowing it down weekly. If it's some remote mount of a probe type that should probably be set up with it's own blow down and again being checked weekly.

I suspect by your descriptions there is something seriously wrong with your installation. Probe type LWCO are fairly dependable and shouldn't need that much attention. Could you post some pictures of your installation?

Abracadabra

pics

tonylap

Apparently the redundant low water cut offs were not piped through the dwell of the boiler. They were piped into the an alternate tap horizontally parallel to the single low water cut off tap. I was told this alternate installation was as prescribed by Weil McClain for the redundant low water cut off set up we had. Because of this this set up the probes were not inside the boiler rather they were in nipples that water fed through the boiler. My installer is now going to install one low water cut off in the single tap that allows the probe to be in the dwell and the second one in the parallel tap plumbed with a bleeder valve to allow periodic flush of the nipple of the probe. It makes some sense to me if the the sludge was the actual cause of the malfunction. Unfortunately the boiler was taken apart before I could take a picture.

JUGHNE

If this picture shows up it is a LWCO probe with blown down valve. The probe is mounted in a 1" X 1/2" X 1/2" tee screwed into a short nipple into the boiler. The 1/2" branch has a ball valve added and piped into the bucket where the primary LWCO is blown down.
This probe blown down will not test the probe, (unless you drain a lot of water out thru it), rather it insures the 1/2" nipple and insertion cavity are free of sludge and has active non stagnant water flowing to it.

Big Ed_4

Sludge mud is call solids . Minerals left behind when water in the system boils off and leaves the system . It is not normal .. Cheaper to fix the steam leaks .... Constant fresh water will eat away ferrous heating system ...