Hydronic boiler pressures

Billyblood

I have 3 boilers here at work that operate on lead and lag. the pressure relief valve on each boiler is set for 40psi. As of late the pressures have been bouncing between 25 psi and 40 psi. because of this one of the boilers is spitting at the relief valve. My question is why is the pressure bouncing around all of a sudden when to the best of my knowledge it used to stay put at about 25 psi.

Jeff Krawic_2

pressure?

If the pressure is "rising" when the burners are running, you most likely have an expansion tank problem ex:
1) Tank has lost some or all of its charge (Bladder tank)
2) Tank(s) have damaged or toasted bladders
3) Undersized expansion tanks.

Now if the pressure is doing this weather or not the burners are running, then look at the feeders, however it is typical that the problem is usually identified WRONG on the feeders,.... so be careful.

Also I am assuming this is a "hot water" boiler and not steam.........

Billyblood

Boiler pressure

you are correct in thinking that they are hot water boilers. i will be cheking the expansion tank to see if that is causing the problem but I will need to get specs on it first. It is a large TACO expansion tank that serves all three boilers.I"ll let you know what I find.

Thanks,
Bill

steve_38

also

Check the feed valve! useually when i'm at a call for
a relief valve leaking. I end up replacing the 1/2" feed
valve, 3/4" male or female relief valve, and the extrol
tank or if it's an expansion tank it gets drained. and sometimes if there is an old gate valve before the expansion tank they may not seat/close all the way and the tank cannot be drained unless a new shut off valve is installed, most likely a ball valve would be a good replacement for a gate valve. When all is done, open feed valve and pressurize the system, purge zones unless you held the system on a vaccum while changing parts and only if there's a Vortech/airventing system. when sytem is pressurized before you turn the burner on make sure the pressure is set at what the feed valve is set for, because if pressure rises in a hydronic heating system with a tankless coil with the burner off, there may be a leak in the coil... steve