Dumb de Dumb, Dumb

Eddy

My hydronic system with a cast iron boiler that feeds multiple air handlers and re-heat coils was recently "upgraded" to a primary/seconday loop set up so I can reset secondary loop temp using outside air temp as the input. Since it was installed, every time the boiler fires, my pressures go nuts (suction & discahrge) and blow the safety valve on the boiler. I checked the bladder tank and it was flat. I replaced the leaking badder (which I asked the engineer to include in his design)charged the tank with air and hooked it up. Still the problem persists, as if I had no expansion tank. Then, I looked at the piping. The secondary loop which used to be the primary loop had the expansion tank on it and not the added primary loop. Am I correct to say that's the problem? I want a little backing before I embarrass anyone, myself included.

Bryan_16

Where are the pumps located in relationship to the tank? Is new primary pump oversized?

Ken_40

Recheck

the bladder. If it was "flat" when tested, it may be flat again!

Unless there is a HX between the primary and secondary loops, the pressure rise should not be that high. Unless of course a high head pump is sucking the water through the loop(s) and not "pumping away." Just remember, pumping away does NOT mean pumping away from the boiler; it means pumping away from the suspect expansion tank!

Eddy

The primay pumps have no physical connection

to the expansion tank. Only via the 3 way valve do they ever "see" the expansion tank. The primary piping and pumps are smaller then the secondary loop.

Eddy

I leak tested the expansion tank

before installing it. It "tees" into the make up line which tees into the suction side of the secondary loop pumps. Actually, there's 3 loops. The third loop is fed from the discahrge side of the secondary pump which feeds the suction side of the perimeter zone pumps. The secondary loop pumps away from the primary mixing valve.

Brad White_9

Might the 3-way valve

be isolating the major system volume from the expansion tank? If the 3-way closes to one position, it may in effect not be allowing the expansion tank to see the expanding system volume. Can you post a diagram?

Eddy

Sorry,

I do not have a scanner available to post a drawing. At this time I believe there are 3 things that need to be correceted. Upsize the expansion tank (the old system shared 2 tanks now there is one). Re-pipe the expansion tank to the primary loop (it's now on the secondary loop) and eliminate the check valve in the expansion tank connection to the system.

Mijola

A check valve in the expansion tank connection to the system? The expansion tank must be allowed to "absorb" the expansion of the water when it is heated, and "return" it to the system when it cools down. If there is a check valve in this connection, the water can't go both ways. Eliminate the check valve before doing your first two suggested corrections.