While I was at work yesterday I had a call from my wife at home saying that the ERV was making a funny noise. I told her to unplug it (just Google for HRV recalls related to fires) and I'd deal with it when I got home.
When I got home I first have to spend 1/2 an hour snowblowing the plow poop and drifting snow that had accumulated over the day (wife is scared of the snowblower and will shovel rather than run it). I finally got in the house and headed downstairs to look at the ERV and saw water dripping out the corner
With towels and a bucket to hand, opening the cover revealed the thing was 1/2 full of slush. I took out all the parts, emptied out the slush, dried off as much as I could with towels and left all the parts to dry overnight. I put it back together this morning and it all works
Looking out of the window gave a clue to what happened. With the winds and the snow yesterday the drift is all the way up to where the intake is and so it must have been sucking the snow in. I was surprised that the slush managed to get through the filter and the fan and was even under the enthalpy wheel, but I guess once the filter was wet it was drawing the water off the filter and then refreezing as slush further through the system. I've left it turned off with instructions for when the 12 year old drags himself out of bed to go shovel the snow bank away from the intake.