Posted by Harold Kestenholz - Hydronic Network on June 14, 2001 at 20:35:06:
In Reply to: Re: Summer shut down clogged system posted by Peter Lothian on June 13, 2001 at 15:37:45:
That would be scary information if this were a steam boiler. Sludge builds up to form a barrier insulating the boiler metal from the water, so the bottom of the boiler can burn through. During the heating season, it is a good idea to drain the low water cutoff and the bottom of a steam boiler once per week.
If this is a hot water boiler, then draining the system is not necessary if it is a sealed system because fresh water with new oxygen and hardness was not added to make rust which makes sludge. If there was a leak all this time there is probably a coating in the bottom of the boiler because lime comes in with fresh water (it is not made from boiler insides), so while all the leaks are being repaired (which means the system has to be drained some anyways) you can flush the bottom of the boiler. You can see if leaks exist by SHUTTING the hand valve to the pressure reducing valve and watching the pressure gauge for some days in the off season to see if the pressure holds steady (no leaks) or drops below 12 psig (a leak.)
If there have been no leaks before, and as you do not know the condition of the inside of the boiler, it may be a good idea to flush it and refill it immediately. Don't leave it full of air to make rust for any length of time. This is a good opportunity to add a low water cutoff control to the system if there is none.