McKenzie’s Boiler Blog

TESTING THE LOW WATER CUT-OFF

As mentioned in a previous post, one of the most important safety controls on a boiler is the Low Water Cut-off of which there are two on a boiler. Both the primary and the auxiliary LWCO need to be tested on a regular basis to keep your boiler operating in a safe manner.

Here is a procedure our service techs use to check Low water cut-off’s -

1. Blow down the water column and observe that the water level in the sight glass returns quickly.
2. Confirm that the shunt switches are working properly.
3.  Place the boiler control in manual and set the firing rate at a minimum.
4.  Observe the water level in the sight glass.
5.  Close the feedwater valve to the boiler in order to generate a slow drain condition.
6. Confirm that the feedwater pump re-circulation line is in place and operational, so that the pump will not dead head.
7. While the boiler is operating, observe the water in the sight glass noting where the first LWCO shuts the boiler off. Make sure the water level does not leave the sight glass.
8. Open the feedwater valve to the boiler in order to establish a normal operating condition.
9. Again, observe the water level in the sight glass.
10. Override the first LWCO, take note of the water level in the sight glass, and operate until the second LWCO shuts the boiler off. Remember; do not let the water level leave the sight glass. 
11. Open the feedwater valve to the boiler in order to establish a normal operating condition.
12. Reset the second LWCO.

We also replace the low water cut-off gaskets as part of our standard maintenance procedure. In fact we include these with many of our gasket kits that we provide for boilers.