Newly refilled hydronic system- proper max pressure

pfmet

our boiler sprang a leak Saturday night

It can just be made out along that pale red line across the center of the photo above. With enough water drained from the boiler(not much) the pressure dropped to zero and the leak stopped. It had been leaking ~1/2 g/hr at the end of the day Monday. We were fortunate to be able to collect the water in an oil change pan and using a thirty mate bilge bump get it into a buckets to dump. After two days of refilling with the auto fill there was much entrapped air in the system at bedtime Monday night so I shut it down. Today Iran a hose from the boiler drain outside and drew off a tiny bit of water. After it dried out I hit it with the wire wheel real

well, scrubbed it clean with Acetone on a rag till the rag came out clean, and applied this stuff.

This ain’t Grampa’s J-B Weld.

this was the result and 4 hours later I flushed the air out of the system as per many descriptions on this site and elsewhere. Let the auto valve fill to what appeared on the gauge to be 12 psi. Opened all the appropriate valves and fired the burner. The boiler had been off for ~18hrs so was lukewarm warm. Didn’t time how long it ran but it came up to temp and the pressure rose to 28 lbs. 25 year old gauge, so who knows. It is short cycling as the house is rewarming and demand is constant. We are way over boilered I know. Long story. The replacement due shortly is properly sized.(Better anyway).

Regarding the pressure, it filled to 12 psi cold. With the boiler now up to temp it is hovering between 22 and 28 as it cycles. No ominous signs from the 30 psi blowoff valve. So, all good? Seems like we’re living on the edge here. My first forced ghetto fix on a boiler which I see everywhere is doomed in short order. But it’s a fun experiment as long as it’s safe, it appears to be working and I will shut in down at bedtime again regardless. My heat contractor is distracted by a sudden family illness so I’m not bugging him and I need tokeep warm. I have a great working woodstove we haven’t use in years. There’s always that. But I have a 1200 ft slab on the first floor to heat that part of the house so I’m trying to keep that warmed up. Hopefully the ship will stay afloat for a couple more days till the deed gets done. 🤞

This is the repair 1 hour after firing off. There is a slight damp spot at the left hand side. Doesn’t drip, just gets wet then dries during off cycle. So far so good. Sorry for the long windedness, a trademark I’m afraid. Any thought on the pressure would be welcomed and greatly appreciated. Thanks to all. Best wishes with all your projects.

EBEBRATT-Ed

Normal pressure is 12-15 with a cold boiler. When it is as hot as it gets you should be 20-22 at the most. 12-15 is enough pressure for a 2 story house. You need roughly 1 psi for every 2' of rise from the boiler to the top of the system plus 5 psi. So for 40' height you would need 25psi.

Either your PRV is not adjusted right ….leaking by or your expansion tank has failed or is water logged.

With the patch I would measure the height from the basement floor to the highest part of the system. Divide that # by 2.31 and add 5 psi to that.

With the patch I would run the lowest pressure you can run. You might get away with less than 12-15 if your house is lower than 2 stories.

pfmet

I found the Watts document on servicing the SB1156F auto fill valve

my question is, when I go through the process of lowering the set pressure, (tag shows 10psi min), how does the excess pressure get relieved? Will I need to connect a hose to the boiler drain and bleed off some amount of water? I see no way for the pressure to simply drop. It can’t relieve itself back through the valve against 65 lb water system pressure…correct?

Pressure was at 15psi cold this am when I fired the boiler. It rose to 25psi at 190deg high limit shut off, then slowly dropped during off cycle. As it had done last night so all seems steady/predictable at this point. I have a 10’ rise to top of system so absolute min pressure would be ideal for preservation of my band aid. So far so good but I’ve not heard from my contractor and this fix MUST last.

Thanks folks for your kind input, it’s much appreciated by the anxious homeowners.

SuperTech

That increase in pressure is an indication of not enough room for expansion. The expansion tank might have failed or needs to be recharged with air. You will need to isolate the expansion tank and drain the boiler pressure from it. With zero water pressure on the boiler you set the air bladder charge to the fill valve pressure. Typically 12-15 PSI for a two story home.