Which RadonAway fan is this

We had the same thing happen to our system. During the winter, water accumulated under the concrete where the radon pipes went into the basement slab and totally blocked the air flow causing our radon levels to go up. We have a 24/7 radon alarm that showed the higher levels. We ordered a new fan but that was not the problem. We cut the pipe near the basement floor and installed a "y" with a clean out cap and used this to pump out the water with a small pump. The pump had to be primed first but after removing 15 gallons, the radon pipes no longer gurgle. Be sure to put the clean out cap back on!

Our u-tube shows a 2" WC. IMO, the hole is the problem: the pump is sucking air from the basement, making both sides of the tube at the same (basement) pressure. Hence, 0 pressure difference. This will obviously reduce the suction from the subsoil; at the same time, it will be pulling radon-contaminated air from the basement. I have no idea what the net effect would be.

You could get a continuous radon monitor. (Amazon, $130) Not cheap, but I find ours very reassuring.

FYI, a couple of things, from experience with our system. (It doesn't seem like these apply to your problem, but just in case.)

1. We've had the outlet ice up in winter. (Moist air from sump, cold pipe.) When this happened, we showed 0 pressure.
2. We've had problems in summer, where a water bubble developed in the u-tube. This affected the reading, but I don't remember how much. At the time, we were drawing outside air into the basement, and getting a lot of condensation. So, warm air, u-tube in contact with the cold pipe. We now keep the cellar mostly closed in summer, and I spaced the tube out from the pipe.