Boiler autofill question

joe85

Hi all,
I recently replaced a few items on my boiler (expansion tank, auto fill, pressure relief valve). It's been working good since, the boiler pressure is sitting right around 16-17 psi when hot which seems right for a large 2 story house (3000 sqft).

I checked the other day that my autofill was  working and let some water out with the pressure relief valve and the autofill did not start introducing water back into the system until it was around 6 psi, which seems low. I know I can increase the psi with the adjustment screw on top of the autofill, will that cause the overall psi of the boiler to increase or will it just increase the psi at which the autofill kicks on?
Thank you! 

Jamie Hall

That is a bit low. See if it comes back to where it belongs (you had it just about right!) and, if not, try the adjusting screw.

joe85

Jamie Hall said:

That is a bit low. See if it comes back to where it belongs (you had it just about right!) and, if not, try the adjusting screw.

Thanks for responding! So once the autofill does come on the psi goes back up nicely to right around 15psi. It's just that the autofill doesn't start introducing water until the boiler gets to around 6 psi which seems too low, maybe I'm wrong? I would think the autofill should kick on and start introducing water somewhere between 10 and 12 psi.

STEVEusaPA

Could've just been sticking. I always check pressure with my own gauge.

EBEBRATT-Ed

@joe85

It might be possible that it was feeding at a low rate and you didn't think it was feeding. I wouldn't test it by popping the relief valve. They have a habit of leaking if you do that too much.

Also, do you have a backflow preventer. If so it should be upstream of the autofill. I have seen them put in downstream and they don't work that way

dave1234

Don’t everyone fire at me at once… my thoughts on PRESSURE REDUCING VALVES… valve it off. A building freeze is SIGNIFICANTLY cheaper and better off than a freeze with a flood on top of it. Trust me. I’ve seen the aftermath. If the boiler goes out your far better freezing and dealing with frozen burst pipes that at least can be dealt with in a controlled manner which is gonna suck absolutely- pressure reducing valve or “auto fill” valve=burst and water keeps on coming- flooding the building. I’ve seen icicles bursting through sheeting and siding. Trust me- your better off without it. That’s from experience and more than one personal eye witness accounts. 

dave1234

Of course it will happen on a long weekend when no one’s around to catch it (commercial) or worse homeowner on vacation. 

Fpipes

I would say that most systems have a way of loosing pressure via packing glands or pex connections etc. Given that I would suggest against valving off as your chance of a frozen pipe is greatly increased when loss of pressure does not permit circulation. We don't shut the water off to our whole house everyday either. 

Fpipes

I would keep the pressure at 15 to 20 cold and 20 to 25 hot for a two story . And as long as it kicks back in and gets back to pressure within reasonable time I would not worry. Under 20psi hot seems low

hot_rod

Have have you or anyone you know had an Autofill flood?

If you valve it off, why bother even installing one?

maybe a fill tank like an Axomin is a better choice. You have some reserve, and a very tiny flood potential

And the yearly backflow testing goes away, if an RPZ is required

dave1234

hot_rod said:

Have have you or anyone you know had an Autofill flood?

If you valve it off, why bother even installing one?

maybe a fill tank like an Axomin is a better choice. You have some reserve, and a very tiny flood potential

And the yearly backflow testing goes away, if an RPZ is required

I’ve absolutely seen it. That’s why I say this. 

dave1234

Fpipes said:

I would say that most systems have a way of loosing pressure via packing glands or pex connections etc. Given that I would suggest against valving off as your chance of a frozen pipe is greatly increased when loss of pressure does not permit circulation. We don't shut the water off to our whole house everyday either. 

No we don’t but frozen water idle- I.e no flow will granted will freeze- expand and ICE burst through the copper on domestic water lines. Circulating water from down water loop there is NOTHING to shut it down=flood. Granted still have the pipes to deal with but can be done in a controlled manner once caught. Far better than a flood on top of it. 

dave1234

Kind of why up here with where we can and do see 30 below weather it’s recommended to leave a trickle of water at highest faucet especially with crawl spaces- the constant flow decreases chances of freezing. 

dave1234

hot_rod said:

If you valve it off, why bother even installing one?

If it was me I wouldn’t. I see a lot of buildings totally isolated loops- fill=bust out the hose

EBEBRATT-Ed

I have done plenty of glycol systems that were 100% tight and had no make up water connection. It's a non issue. I would make sure to have a good gauge (or two) a low water cut off and leave it valved off if its an issue. Just check the pressure occasionally.

LeeGran

hot_rod said:

Have have you or anyone you know had an Autofill flood?

I had an Autofill flood a couple months ago. It was a fu*king mess. Luckily, I had a guest staying in a basement bedroom that alerted me to the water on the floor. It took a few minutes to figure out why the relief valve was pouring out water. The Bell & Gossett "Pressure Reducing Valve" was only about 10 years old. B&G stuff used to last 30-40 years. It think it all started with a dripping automatic air vent. So the Autofill was always working.

In the future, I'll shut the valve on the Autofill. I check the boiler often enough.