possessed Weil Mclain CGI

Rob10667

O.K  I'm out of Ideas. 

   About a week ago A weil-mclain boiler at a very good customer's house started relieving for no apparent reason. I checked all the usual suspects without success.  Pressure reducing valve, check.  Expansion tank, check.  Even replaced expansion tank out of sheer desperation but still have the problem. Closed the hand valve upstream of the PRV in case it was leaking through. no luck. This is about a 6 year old boiler 233,000 btu. It has 5 zone pumps attached to 2 zones of 100 year old cast iron radiators and 3 hydro air zones serving the newer additions. The pumps are on the return side of the boiler (we didn't install this) the #60 expansion tank is immediately off the supply along with an auto vent.

There are also 5 B/G weighted gravity flow checks on the supply header.  No matter what I do i can't keep the pressure from gradually rising (sometimes it takes overnight) and popping off.  No changes have been made the system and it has worked perfect for six years.  Fresh glycol was put into the system last October. This problem manifested itself about 10 days ago and has been a constant thorn in my side.  Haven't had my butt kicked like this in about 20 years.  Any helpful comments would be greatly appreiciated.

Big Ed_4

Pressure Build up

let's do the process of elimination .. if the pressure builds on temperature rise , you don't have enough expansion .. if the pressure rises when the circulators  run , it's the location of the feed valve... if the pressure increases and the relief valve stays with a constant drip. higher pressure water is by passing into the system. 



Now you replaced the tank .. Was it adjusted for proper charge ? Has the system been increased beyond the #60 ? 



  You shut off the feed , is the valve holding?



  From what I read , it steady increases with a steady drip ..??? 



  Is there a heat exchanger , hot water coil or indirect connected to the system ?? Can they be leaking ? Any plumbing done in the building ? Did some one pick up hot water from the heating system ? 

Rob10667

pressure rising in the boiler AND this big vein in my head!!

ED,

thanks for the response,  No changes have been made in the system since we've been servicing it.  I've virturally eliminated the feedwater system because the system is always full of air when I get on-site. but the boiler is always at 30# with a steady drip through the relief. (with lost of system gurgling)  The system has approx 125 gallons of water with the boiler and operating temp that #60 Xpan tank is marginal at best. but it has worked fine for six years so WHY NOW??

Al Letellier_21

dripping safety

I think the key clue here is fresh glycol solution. IF that new antifreeze is a stronger solution than before, and the X60 was marginal, you need more room for expansion. Add a second tank. 225 gallon is a lot to solution to heat up. It's the only thing that makes sense as you've eliminated all the other possibilities.

Unknown

Had that once,,,,

with another manufacturers unit.

Turns-out one of the pumps impellers was getting plugged at the "eye" causing the boiler to cycle on H/L,,, eventually one of the other zones called relieving the high-temp water and the valve tamed-down,,,,, but when it was only "that pump" trying to circulate the RV problem resumed again.



Was pulling my hair-out for awhile,,,, :-)

Mark Eatherton

I agree with Al, plus...

Glycnoids have a higher co-efficient of expansion than do straight water (hold the rocks). Now that the system is FULY heating up, you have more hot gallons of extremely highly expansive fluids, and a relief valve that is doing what it was intended to do. BTW, you can put a smaller expansion tank in with the bigger tank. Just make certain they are both connected to the piping in the same spot.



You have stated how many gallons the system has in it. How did you determine that and how many gallons of glycolization occurred, as a percentage?



I have Siegenthaler's program that will tell me how big the tank needs to be, and how many PSI you need on the diaphragm side of the tank to avoid lifting the relief valve. ALso need to know the overall height of the system from the boiler to the highest component.



The reason you have a continual air problem is because of the pumps being on the return, and I assume they are pumping towards the expansion tank (PONPC). Move them to the boiler outlet, making certain they are pumping away from the PONPC, install an air separator/eliminator and your air noise issues will go away.



Guaranteed.



ME

jgrossman

Relief Valve

I have had this happen a time or two and it turned out to be the aquastat was sticking and keeping the burner on periodically, causing the water to overheat and pop the relief.  It was hard to id because it always cycled as it should when we were there. 

Rob10667

Thanks guys!

 OK,  I buy into the glycol theory and I KNOW the expansion was marginal.  My only question still is why didn't this problem show up in october when the glycol was first pumped in, why now four months later!!  Today I twinned in another #60 with the existing one and we'll see.  Sometimes it take a day for it to do it. I'll post an update in a couple days if it behaves itself.   Thanks again for all the good advice!!

Rob10667

Last chapter and worse!

Mystery solved!  (finally)

This weekend my nasty little weil-mclain gave up a section.  So.....

I proceeded to tear down this boiler, remove the cracked section, reassembled the block (now one section shorter) On Super Bowl weekend, in the middle of a blizzard, out of the back of a Jeep Cherokee, (van was snowbound).  BTW if anyone ever has to do this, You have to blank off the missing section in the base with sheet metal and plug the burner orifice. BUT... don't blank off the flue collector hood because that causes too much velocity through the remaining sections and extinguishes the interrmittent pilot.

Anyway, this boiler was nearly full of scale and mud and my excessive pressure was coming from water trapped in the superheated sections and flashing to steam. Although it didn;t pop and crack like normal (THAT would have been a handy clue).  ANYWAY. Thanks to eveyone for all the helpful suggestions.  I'm gonna go sell a new boiler!

Rob

Unknown

WOW what a weekend you had!

Glad to hear you identified the problem,,,, kinda similar to what I went through. :-)