How Often Should Auto Water Fill Boiler?

Never

Auto-feeders are a safety device to prevent the boiler from running out of water and leaving a building with no heat if a small leak develops. They are not a convenience device to take the place of routine maintenance. So if you're checking your boiler weekly, flushing out the sediment and topping up the water level, you shouldn't ever find that the autofeeder has been activated. They should be set to come on only when the lwco indicates a low water condition, and that should never happen under normal conditions.

that's fine

Nope, that's fine.  You are emptying the water that the float is floating on.  Float drops and the feeder feeds water.

Ordinarily not

There are two things that can make an autofeeder activate, other than deliberately causing a low water condition for testing purposes. One is that there is a leak in the system that is causing an actual low water condition. The other occurs when the pressure in the boiler delays the return of condensate, causing a temporary low water condition, which activates the feeder to add water, then, at the end of the heating cycle, the condensate returns, and the boiler is overfilled.



A leak that goes unaddressed eventually gets worse, and can cause considerable damage whether it is a steam leak or a water leak. In the second scenario, gradual overfilling can lead to flooding, where the water level rises until it finds a place to leak out, like a main vent or radiator vent, and it usually picks something expensive to leak on.



If you're being careful to refill the boiler every time you blow down the LWCO, but the feeder still needs to add water to maintain the normal level, you need to find out where the missing water is going, and the more missing water there is, the more urgent it is to find it. If the water feeder makes the water level end up higher than it should be, instead of looking for a leak, you need to make some adjustments to keep if from overfilling. Sometimes it's just a matter of lowering the LWCO or adjusting the feeder, but if the water level is fluctuating a lot during the heating cycle, you might need to raise the Hartford loop. This modification is sometimes called a Gifford loop. (See http://www.heatinghelp.com/files/posts/1196/HPACGiffordLoop.pdf)

Could be a few bad vents

If it's a big system and has a few bad vents, it could be losing steam that way, but it's the kind of thing you really want to track down instead of just assuming it's nothing serious. I used to think it was normal to lose a little water during heating season, then I got a call from my wife last November while I was at work telling me there was water on the basement floor. But that's small potatoes compared to a cracked boiler, which can send the water up the flue so you'd never see it, especially if you weren't looking for it.



Hopefully it won't turn out to be anything serious, but if it is, you want to find out before it becomes an emergency, so you can get it fixed over the summer instead of having to deal with it in the middle of next winter.

Check the

Valve packing, better still re PAC each valve, takes about 5 mins per valve (for a pro) and it could save a boiler long term. Also you should have a water meter, built in or otherwise.

Yes

You could also have vapor leaks. I would re pack them all