Low water cut out only works when burner is off

charliechicago

Hello to all

I was doing a steam boiler maintenance and was checking the low water cut out and it did not shut off even though the water level was well below the probe. At this point I turned off the burner so it would not continue to run. After 10-15 seconds it registered low level (yellow light on the cut out turned on and the vent damper closed) I tested it four times and it repeated this every time. The sight glass and the probe are on the same side of the boiler so I would presume the low level I am seeing in the sight glass is also a low level at the probe.

Any ideas?

Thanks in advance.

charliechicago

I cleaned the probe and checked wire connections at probe but that didn't help

ethicalpaul

This is because the boiling water splashes onto the probe and makes it think water is there (which it is). I have seen this occur as well.

This is why the Cyclegard LWCO exists which every 15 or 20 minutes stops the burners for 60 or 90 seconds (depending on model) in order to test the level of quiet water.

This is why several manufacturers ship their boilers with this device. Unfortunately, the 1 minute pause 4 times per hour annoys installers, generally speaking, so they make the incorrect in my opinion choice to remove this very safe device, throw it into the junk pile, and replace it with a similar device that doesn't stop the burners to test the water level.

charliechicago

https://forum.heatinghelp.com/discussion/comment/1875159#Comment_1875159

So you are saying this is normal ?

Someone suggested this occurs because of dirty water, priming, foaming etc and that I should clean out the boiler.

It does actually have a CycleGard CG400

ethicalpaul

I think it's normal, because I have seen it happen too. And plus, otherwise the cyclegard wouldn't exist.

OK you have a Cyclegard. What does it do when the low water test occurs?

EBEBRATT-Ed

Read the control instructions. Most (maybe all) probe type controls don't shut the burner down the instant the water goes below the probe. They delay for some time period.

charliechicago

https://forum.heatinghelp.com/discussion/comment/1875184#Comment_1875184

I haven't seen it cycle off on the test

ethicalpaul

OK well it should happen after 15 or 20 minutes so let it do its thing and see if it can detect the low water level during its test phase.

Now you did ask about if you needed to skim your boiler. Does the water level stay more or less constant, like within one inch to 1.5 inches of variance during a call for heat? Or does it dive down to the bottom of the gauge glass? If it's the former, then your water is clean enough.

charliechicago

https://forum.heatinghelp.com/discussion/comment/1875185#Comment_1875185

I hear your point, but it was definitely below the cut out level for a while without shutting off and every time I turned off the burners it shut off within 5-10 seconds.

109A_5

As a sanity test, instead of lowering the boiler's water level what happens if you just disconnect the probe ?