Why does my 2.0 L BrewKettle (BrewMaster 3000) lose pressure after I switched to a 15‑° mash schedule?

I’ve been wrestling with the BrewMaster 3000 2.0 L kettle for a week now. After I dropped the mash temperature from the usual 68 °C to a cooler 53 °C (trying that 15‑° swing some forum guys rave about), the pressure gauge on the lid never climbs above 0.3 bar, even though the pump is set to 2 L/min. The wort looks fine, but the airlock barely bubbles and the temperature controller (ST-200) is flashing ERR‑08.

I double‑checked the O‑ring seal, the vent valve, and even swapped the pump with the one from my 5‑gal fermenter – same result. The only thing that changed was the mash schedule and the fact I’m now using a 0.5 mm stainless‑steel sparge screen instead of the 0.8 mm one I usually use.

Anyone else seen this? Is the lower mash temp somehow affecting the headspace pressure, or am I just missing a step? I’m about to dump the batch, but I’d rather figure out if the kettle itself is defective before I toss the whole thing.

• Tried: re‑gasket, vent reset, pump swap, screen change
• Still: low pressure, ERR‑08 on controller
• Equipment: BrewMaster 3000 2.0 L, ST‑200 temp controller, 0.5 mm screen, 2 L/min pump

Any thoughts or similar horror stories appreciated.