boiler blowing off

chris_40

I went to a call today and boiler blew off gas fired buderus ga 244 I replaced expansion tank and relief valve what else could cause this fast fill, and does the high limit have anything to do with this thanks

Empire_2

Thoughts

What is the pressure on the boiler? Could possibly be that the PRV is leaking by, or not actually filling and making steam..etc... You may be over heating, but without info, it's just an educated guess. Fill boiler to 12 psi and shut down water supply to boiler. Watch and cycle as normal and see what happens..

Mike T.

Unknown

check the DHW devices/exchangers

had one of those a couple months ago, a real head scratcher. turned out to be the tankless coil that had developed a leak in the exchanger. might be something to check in your case if they have one, or an indirect tank.

Brad White_68

And don't forget to consider

the size of the expansion tank..., especially if it is connected to an older gravity system with lots of pipe and radiator volume.

Whatever type of system, was the ET at least properly sized based on volume? Rather than replace it, I would add others of the same type to reach the required acceptance volume, but make sure that they all are on a common leader pipe to one PONPC.

Too often an undersized ET will work fine in the lower temperatures and when run to high limit or for DHW production, that is enough to invoke Boyle's Law.

Do watch the pressure and temperature at the same time. If it leaks at all temperatures, especially when off, I would suspect a leaking DHW coil or fill valve/bypass valve. If that is the case you should be able to hear it on a still, quiet night when the moon is full...

Just an add to Mike T.'s and Zac's points. A good handful of variables.

Big Ed

Blow off

If it mantains high pressure and the relief valve drips constantly ......The water is feeding in....Feed valve ,heat exchanger or someone plumbed into the heating system by mistake..

If the pressure builds and the valve releases on temperture rise ......You don't have enough expansion...


If the pressure builds when the circulator runs......Its the location of the feed valve........

Erratic Leaking..... very rare but would like to add.... Someone plumbed into the heating system by mistake or a indirect leaking under a cooled down cycle.... Seen both

Jerry_15

Be careful that the x tank you put in is at the right system op pressure. If it was a potable tank it's preset at 60psi or so, and thus worthless. You have to bleed it down. Even the hydronic tanks are sometimes dead out of the box, and should always be checked. It could also be going to steam from lack of circulation, air-lock, etc. Good luck
PS Once the relief valve trips be ready to replace it. They don't like that.

Unknown

jerry's right

Jerry's right about matching the pressure as well the size of tank to the existing system... Question that I have to ask for the wallies... I was told by the state plumbing inspectors that we suppose to size the ET according to amount of the water heater btu input... Is that right?

Jerry_15

Brad-help

I have never understood the relationship between btu's and xtank size, although it comes up frequently. The xtank is dealing with the expansion of the water volume in the system. If someone can explain to me why a a system with a total water content of 50 gal needs one size tank with a 500k boiler, why would a mill boiler change the tank size, wuth no change in the water content?

Mike T., Swampeast MO

Jerry,

See this document Amtrol Brochure

Two different sizing methods are mentioned; one based on boiler output & type of radiation, the other based on system volume and temperature.

I believe that the boiler output & type of radiation method is a "rule of thumb" method while the system volume and temperature is the "real deal".

An inexpensive device like this Garden Flow Meter would likely prove very useful for a very reasonable estimate of system volume.

Brad White_9

BTU's and Expansion Tank Size

The "BTU Method of Expansion Tank Sizing" is like sizing a locomotive engine fuel tank based on the size of the conductors hat. Or something.

For heating systems is at best a rule of thumb and was based on copper (read: small diameter compared to gravity HW) tubing sizes. It is still a guess but the tables are experiential. They work but only when the parameters are understood and -miraculously- coincide with real-life!

As Mike T. posted with the material from Amtrol, you can see what I mean.

The habit of using the BTU method is so ingrained, it explains why so many converted gravity HW systems have such wet floors near the boilers.

As Mike T. said, a water meter is a great tool to get a real volume number.

Mike T., Swampeast MO

To my surprise the "BTU" method produced a barely acceptable selection (SX-30V) for my converted gravity system. ONLY however because I used the output of the RADIATORS, not the boiler! Used 170 btu/hr/sqftEDR.

If I ever have to replace the original 30-gallon plain tank, I'll probably use a Model 90 + a Model 60. If I wasn't 100% positive that any rationally sized boiler connected to the system is incapable of raising the entire system past 170° or so, it would be two Model 90s.

Jerry_15

Yeah, that all makes sense to me. I have tried the btu method when it's a hassle to calc an existing system. Might work when the boiler is grossly over sized, but I only use it as a cross check. I usually make an educated guess, over lunch, and size it up a notch or two depending on the size of the building. I hate multiple tanks. By the time you get done piping, hanging, and sometimes strapping, you could have put a nice floor mount with some extra volume to boot. Looks pro and clean, and since it's not in the pipe stream, you don't have to worry about what side of the pump, etc., and can stick it anywhere you want with a 1/2" ball-valve and easy piping. Bigger is not always better, but it don't hurt, and I never get call-backs.

Jerry_15

Regarding building inspectors the rule is: Those who can: do. Those who can't: teach. (excepting Dan of course) Those who can neither do or teach, become building inspectors.