Safe to close valve for incoming water on Hydronic boiler?

dgvEP2020

Hello.
I have a two zone, two TACO pump, hydronic gas boiler system with expansion tank. The boiler is probably over 25 years old but I can't afford to replace it this year. The red zone is 30 PSI for the system and my relief valve works, because I've seen it in action. When the system is running I keep the water temp at about 145 Fahrenheit so the pressure stays in the safe zone. If I raise the temp the pressure goes up but I can bleed the system and keep it under 30 PSI at the higher temps, but only for the actual day I bleed it. (BTW-When I do bleed it it's just water that comes out, no air, like it used too.) My guess is that on the overnight when the system is off and the pressure drops and the feed valve puts new water in the system, (I believe it's rated to do so at 15-20psi) which in turn raises the pressure when it's heated in the am. I have a water shut off before and after the feed valve and so my question comes down to this: If I raise the water temp and bleed the system to get the pressure to say 25 PSI, can I safely shut off the intake so no "new" water gets into the system when the pressure drops? What are the dangers of doing so if I go that route? Than you!

neilc

Yes, you're ok to close the valve to the feeder, just keep an eye on it.
post some pictures of the boiler, where the feed is piped in, the circ(s) and the tank, one big shot if yuo can
How are you making domestic hot water?
is the domestic system tied in with the boiler?
there could be a leak from the higher pressure domestic, to the boiler.

Jamie Hall

Or the pressure regulating feed valve could be leaking by.

Further, check the expansion tank. If the system is run at 15 psi cold, it shouldn't rise to more than 20 when hot. If it does, there is an expansion tank problem in addition to the feed (or DHW) leaking.

dgvEP2020

Thank you for the response. I have included a picture. On the right is the vertical domestic water line, the first shut off valve, a back flow preventer, the feeder, second shut off valve and then it meets up with the zone feeds. I have a separate HW heater that uses the same feed but because of the back flow preventer I don't think were mixing.

Jamie Hall

No, you wouldn't have a mixing problem. The only time DHW can cause a problem is with a tankless coil actually in the boiler. So rest easy on that one.

dgvEP2020

Good point about the expansion tank. Any tricks to know regarding checking pressure or pressurizing? It's a 12psi base setting so if I shut the boiler off and the system pressure drops to 10-15psi is that good to check and pressurize or do I need to completely drain the boiler? My plan would then be to shut off all water coming in as well as on the zones which will allow me to just drain the boiler. Once empty then pressurize the tank to 12psi and refill the system and bleed. Suggestions?
And by the way, thank you all so much. It's great to have this for me to learn from.

neilc

dgvEP2020 said:

, , , or do I need to completely drain the boiler? My plan would then be to shut off all water coming in as well as on the zones which will allow me to just drain the boiler. Once empty then pressurize the tank to 12psi and refill the system and bleed. Suggestions?
And by the way, thank you all so much. It's great to have this for me to learn from.

not "completely" drain, just till it shows 0 pressure, and the hose or drain first stops flowing,
no need to glug, glug, (and introduce air),
do as you said, shut off all the valves to the house and isolate the boiler, drain the boiler to 0, now check the air on the tank, 12~13 psi, if you have to add air check the boiler gage again, it may pressurize a little, drain to 0 and recheck air,
then you reopen all valves to the house except the feed valve,
do a hand fill with the feed valve if it needs to make to 12 # on the boiler gage, then shut the feed valve again.
Check your boiler pressure daily for a week(you're not leaking), then once a week(you're not leaking), you're good, leave the feed valve shut, but check the boiler weekly, or monthly(you're not leaking)
I believe your circulator is pulling on your open feed valve, and adding pressure to your system as it is on the pull or low pressure side of your circ, and that tank, ideally the feed would be piped in to the tank line.