Should I leave my boiler fill open?

ryan242

I live in a single story ranch home with an unfinished basement, I have Fujitsu ductless mini splits throughout the house that I use for air conditioning and when the weather is mild in the winter, I have also have cast iron radiators and baseboard throughout the house and there is a 2 room addition that has fin tube baseboard. I use this system when it’s really cold. Last year I replaced the expansion tank as it wouldn’t hold an air charge, had a terrible time getting it off and ended up having the system open for a long period of time and drained the entire system, everything is back together and working but I can hear air in the baseboards in the addition part once in awhile, I’ve bled the entire system multiple times and lately I only get air off the radiator closest to the boiler, my question is should I continue to bleed every couple days or should I let it be and leave the air scoop try and get it? (There’s only about 4 inches of straight pipe between the elbow and the scoop, and the circulator is on the return) and also should I leave the fill valve open all the time or close it and just add water as needed ?

Jamie Hall

If the water is flowing OK through the baseboards, I'd be very inclined to just leave it be and let the air scoop try to get it. it will take a while -- four inches isn't really enough for best operation -- but give it time. If you think of it and have nothing else to do you can try bleeding -- but I suspect you're OK.

On the water fill. You ask six of us and you will get eight opinions. If the system seems to hold pressure well you can probably leave it closed. However... personally I would want to check the boiler pressure very regularly if I did that. And I would want a reliable low water cutoff...

EdTheHeaterMan

I agree with @Jamie Hall however, as a contractor, I would always leave the feed valve open so the auto feed could do its job. The worst thing is to have a customer pay $$$$$.00 for a new system only to have the LWCO cause a nuisance no heat. You can always count on the integrity of old piping systems to cause you problems over time. It is a great insurance policy. Especially since the Homeowners Insurance will cover the damage caused by the a leaking pipe. But you can't build a customer's confidence if you have routine nuisance failures.

Tinman

I keep mine closed and let the LWCO do it’s job. That said, I keep an eye on mine all the time. 

neilc

if you close the valve,
check your pressure 2 X's the first day,
once the next day,
skip a day and check,
then at 4 days,
always doubling your between checks period,
then once a week, once every 2 weeks,
check every 2 weeks.

hot_rod

What type of air purger do you have? Tha cast iron scoop type, when properly installed can take days to remove all the small air So the fill valve needs to be left in to add water as the air is removed

once it is completely silent , air free, you could turn it off

I have always left them on and have not regretted it,

ryan242

hot_rod said:

What type of air purger do you have? Tha cast iron scoop type, when properly installed can take days to remove all the small air So the fill valve needs to be left in to add water as the air is removed

once it is completely silent , air free, you could turn it off

I have always left them on and have not regretted it,

Yes it is the cast iron scoop type, it’s an Amtrol American air purger, the problem I’m worried about is it only has a touch over 4 inches of pipe from the 90 to the scoop

hot_rod

that scoop in that location really is not doing much, and the circ on the return further handicaps air removal 
The best fix would be some repiping and equipment upgrade.
Increasing boiler temperature for a few hours may help expel the problematic air.

Dave in QCA

I'm inclined to agree with everyone's previous comments regarding the residual air. If you have good circulation the air will probably work its way out, especially if you are maintaining the standard 12 psi at the boiler. That brings us to the subject of the autofill. Should you leave the supply to the autofill open or closed. Well, it seems to me, if you have an autofill, and close the supply, then you don't have an autofill anymore. No?
The first radiator system in a home that I owned, was a gravity hot water system. It was just great. The water fill was kept closed because if you didn't, the water just kept running in. There was no autofill. But the good thing was that the expansion tank was high on the wall in the upstairs bathroom. It had a sight glass on the side, and every morning when I got up, I could see the status of the water level in the expansion tank, and I had assurance that the system was doing OK. But that was back around 1982 and much time has passed since then. Gravity hot water systems have become a thing of the past and cast iron boilers with circulators must have special considerations because of the condensation that can come with a cast iron boiler running at cold temperatures. But I digress.
I few years ago I was with a friend and he was showing me his enormous Circa 1960 American Standard boiler. He explained all of the various components (that I fully understood probably better than he). I noticed that his water supply leading to the autofill was shut off. I asked him why, and he said that he just didn't think it needed to be on. I couldn't argue with that. But then a few years later, there was some difficulty with the system, some repairs were made, and when he turned the auto fill on, it would not work. He ended up calling service. The boiler repair company strongly advised him to keep the supply valve in the on position so that the static condition of the auto fill was in its normal operating condition. He explained that often when the water supply is shut off, it allows the autofill to rest in a position where it never moves, and after a few years, can become frozen in place by lime scale or mineral deposits. The autofill was repaired, the supply left on, and no problems have occurred since.
So.... from experience in the field, I have to weigh in on leaving the autofill supply valve open and let the autofill do its job.

PS. Jaimie, good to see you hear and still working hard to help folks solve problems with their heating systems.

Tinman

Another thing to consider is the water quality of the fill/makeup water. It could become a problem quickly with a modcon.