Is Rod Serling in the house?

Steve K._2

Bizarre happenings in Westchester!!

Looked at a job the other day. 2 boilers joined together at the header and return. One unit is 150 HP, the other 200 HP. Boiler heights are very similar. There is a three way motorized valve off the supply header for reset leading to a base mounted pump set.
Here's the problem- The 200 HP boiler blows the relief valve on every cycle. The smaller boiler remains 6 pounds lower. It doesn't matter which boiler is firing- the same difference remains. More fun- shut everything down to see if we can equalize- pressure differential remains.
The expansion tank is on the top floor- an open tank arrangement- does not over-fill and level rises and falls normally. Did some checks using valves in the boiler room, nothing seems to be clogged on tank line or supply and return headers. There are coils in both boilers and we have considered that the one in the 200 HP may be leaking. However, the system does not overfill and when both boilers cycle off the pressure drop a few pounds in both boiler... but the pressure difference remains.

Any ideas or experiences out there???

Thanks

Mark Walnicki_2

quick thoughts

Did you install new gauges? Maybe one or the other, or both, are just "off".

Maybe it's just a matter of a bad relief valve? Does the pressure on the 200hp boiler get to the relief valve setting? Assuming of course, the gauge is good.

You say it blows every cycle. Do you mean it blows everytime it's firing, or it'll still blow even when just the smaller boiler is firing?

Bill Nye_2

Where?

Where is the circulator pump located? is it pumping into the 200hp boiler?

S Ebels

Hmmmmm

Sounds like it could be a flow problem in the 200. Maybe causing the temp and therefore the pressure to spike. Check the piping for bothe and look closely to see if the head through each boiler is balanced.

Has any piping been changed recently?

Is the system pump circulating away from the boilers or pumping into them. If into, a higher head in the 200 would trnalate into higher pressure.

When did this symptom begin? All of a sudden or has it been occuring for a while?

Weezbo

My thought is .....

the pump is slightly oversized,or the impellers creating problems in flow check the maint. schedule and see what was the last work done on the system....

jerry scharf_2

pull both guages

Steve,

You make the false assumption that the guages are to be believed. How clean are the pipes/water in the system. It's not an easy flush for a system that size, so it's easy to believe that it's nasty inside there.

Replace both guages, and clean or replace the pipe each mounts onto. You've probably spent more time than the cost of the guages already.

jerry

Rudy

check your firing rate, I had a cleaver Brooks with a broken linkage a few years back that looked like it was modulating but was really in 100% fire all the time, during low flow/low demand it would pop the relief every time. Eirc