Gas boiler still blowing off!!!

Plumber63

We changed the fill valve, expansion tank,relief valve and it still blowing off every few days. Boiler pressure is set at 20lb and high limit is 180F.



Has anyone ever had this problem, By the way this work was done by a pro!!

Mike Kusiak_2

Tank capacity?

Is the expansion tank big enough to accept the additional volume of water created by thermal expansion? Is this a new system and did it ever work properly?



Otherwise you must have some sort of leak of feed or DHW into the system. Is the DHW also heated by the boiler? The pressure cannot continue increasing unless there is some source of additional water entering the system.

Charlie from wmass

Check the pressure

in the expansion tank and make sure it is matched to the working pressure. Why are you at 20 pounds pressure rather than 12 - 15 pounds? If the 20 pounds is required make sure the tank is large enough as the higher pressure will require a larger expansion tank

Ron Jr._3

I agree with Charlie

Why is the pressure set at 20 psi ? How high up is the heat going from where the boiler is ?  If the PRV is set at 20 psi cold it'll be very close to 30 psi when hot , even with a properly sized expansion tank . If the boiler is rated for it and you really need the increased pressure , I'd bump up the relief valve capacity to a 40 psi safety .

tim smith

Re: expansion tank

What size expansion tank did you put on, I know it is probably the same size but we have run into problems with tanks being marginally sized and even though they worked for prior 5 yrs or so, the new tanks would do the same thing. If I think a #30 extrol may do it, I go to a #60. Real hassle as you have found to chase pressure increase probs. I have had expansion tanks work fine for 5 yrs + and even though bladder still sound, they start to not accept the same amount of expansion they have prior. The only way I have been able to explain it is that maybe the bladder is sticking to the inner wall of tank or maybe the bladder has stiffened. I do not know but have pulled my hair out a few times over the years. Good luck. Tim

will smith_4

Pressure issue

Are you using a diaphragm or steel tank? If it's an old system, could the piping leading to the tank be partially plugged up?

STEVE PAUL_3

DON'T INCREASE SAFETY VALVE BLOW OFF SETTING!!!

With all due respect to Ron,

 I WOULD NOT, replace the pressure relief valve with one of a higher blow off setting. The 30 PSI blow off valve is a code requirement. Using a valve with a higher setting would negate any manufacturers warranty and would be dangerous. After reading all of the previous and valid suggestions the one that I would recommend is to look for an isolating valve between the expansion tank and the boiler, if there is one, make certain that it is wide open. Your present pressure regulating valve setting of 20 PSI seems to be a rather high setting. 20 PSI is more than  enough to fill and purge a system in a 4-5 story building. Your PRV setting usually should be approximately  the highest point of the system in feet, divided by 2.33 + an additional 2-3 PSI... 2-Stories = 20', divided by, 2.33 = 8.58 PSI, + 3 PSI = 8.61 PSI. The 12-PSI factory setting on the PRV is more than adequate

Slimpickins

indirect tank?

If you have an indirect water heater you may have a leak in the coil and the house side pressure is raising the pressure on the boiler side. Isolating the indirect tank will answer that question.

tim smith

Steve, are you thinking I was talking about relief valves???

Expansion tanks!

STEVE PAUL_3

"STILL BLOWING OFF"

TIM:

The original post stated that after the replacements were made, it was "STILL BLOWING OFF".

 After almost 50 years in this racket, I can not think of anything on a hot water boiler that will "BLOW OFF" other than the relief valve. If I am missing something, I can learn something. Please educate me.  Again, I would re-state,  don't tamper with the relief valve, stay with a 30 PSI rated valve.

 Please don't take this response as argumentative, I just would hate to see someone injured or worse.