furnace question

Yes drain, remove plugs, flush, use a hose inside flush clean, fill and run it to remove oxygen in water. Run at least a few cycles but maybe call the mnfg on that.

Why bother? The water in your boiler is as oxygen depleted as it can be. Adding more unboiled tap water later will only cause more rust buidup if that is your concern. Look at any old heating plant parts in a scrap yard and you will note that cast iron is quickly passsivated from corrosion by the continual recycling of the water. The system manufacturer will have literature to guide you if your service people can't provide one. Good luck.

Joe

Why bother, because the crap-mud at the bottom will ruin a boiler in short order and cost thousands to fix.