Is it normal for my boiler condensate line to fill a 5-gallon bucket?

That is definatly your **pressure relief valve** dumping system water, not a condensate line. Real condensate from a high-efficiency unit looks pretty much like tap water. Murky, rusty brown water means you're losing the actual hydronic fluid circulating thru your heating loop. Putting a condensate pump on that pipe woud just mask a serious mechanical failure. Take a quick look at the pressure gauge on the boiler. If it's creeping up near or past 30 PSI when the burners are running, the valve is doing its job to keep the system from overpressurizing. Nine times out of ten, this happens because the **expansion tank** has failed. When the internal bladder tears, the tank gets completely waterlogged. Heating water expands as the temperture climbs, and without that cushion of air to absorb the extra volume, the pressure spikes immediately and lifts the valve seat.

You can give the expansion tank a quick check yourself. Tap it with your knuckle or a wrench: it should sound hollow on the bottom half where the air charge lives, and solid on the top. If it's a dead, heavy thud from top to bottom, the bladder is gone and it needs to be swapped out. The other common issue is a pressure-reducing fill valve stuck open, constantly feeding street pressure into the closed loop.

Get a tech out to look at it today. Running an overpressurized boiler that constantly dumps water is rough on the equipment, and bringing in that much fresh make-up water will rapidly rust the cast iron from the inside out. Whatever you do, never cap that pipe.

Depress the Schrader valve on the bottom of the tank—probly an Amtrol Extrol #30 if you're on a standard residential setup. If water spits out of that tire valve instead of air, the bladder is torn and it's completley toast. Also, plan on having the tech swap that relief valve itself (ussually a Watts or Apollo 30-lb). Once dirty hydronic fluid full of black magnetite blows across the seat, grit embeds in the elastomer gasket and it'll slow-drip indefinitely even after the pressure problem is fixed. Have them throw a Webstone Pro-Pal service valve on the tank port while the loop is drained.

While you're getting that sorted, defintely look into adding an Adey MagnaClean Pro2 to the return line. That dark brown junk in the bucket is pure magnetite chewing up your boiler and circulator pumps from the inside.

Once the tech fixes the pressure issue, have them flush the loop and pump in a bottle of Sentinel X100 inhibitor. Introducing all that fresh oxygenated make-up water will eat right through your cast iron without proper chemical protection.

Before jumping straight to the relief valve, have you acutally traced that white pipe back to where it connects inside the cabinet?

Most codes require PRVs to be piped in copper or threaded pipe, not white PVC. If that line realy is running off your condensate trap or exhaust collector, have you ruled out a failing heat exchanger? If an aluminum or cast-aluminum block is rotting out from acidic flue gas, you can get a surprising amount of murky, rusty sludge draining out with the condensation. What make and model is the boiler? Worth confirming wich port that line actually leaves before writing it off as simple overpressurization.

If your boiler has an internal tankless coil making your tap water, keep this in mind. Saw it constantly back in the 70s and 80s. Those copper coils develop pinhole leaks over the decades. When that happens, your 60-pound domestic street pressure bleeds straight into the 12-pound heating loop, and that relief valve will dump til doomsday. Shut the cold supply valve feeding that domestic coil for an hour and watch the boiler gauge. If the pressure drops back down, there's your culprit. Everyone blames the expansion tank first, but an old coil will fool you every time.

Quick update — you guys nailed it. I pressed that Schrader valve on the bottom of the expansion tank like suggested, and dirty water shot right out. The internal bladder was completely blown, so the relief valve was blowing off all that excess pressure. Tech came by this afternoon, swapped both the tank and the valve, and we're back in business. Appreciate the help!