[noroot]

For this cold spell it's a little too late, but the solution for this to add some heat-coil/heat-wire on the bottom of the heat-pump housing that you can activate in those conditions.

The issue is that the defrost mode will defrost all the ice from the fins, but it freezes again before it can all drain through the small drain hole on the bottom of the housing. It's somewhat a known issue with air source heat pumps, sadly. I've not run into this issue myself, but on a Dutch speaking forum (tweakers) there is a long thread about this modification to "survive" the cold spells with this small modification.

You can manually attack the ice with a heating gun or hair dryer to remove it, but that's a faffy.

I think manufacturers should, and probably will, add something like this themselves in the future.

[willvarfar]

Yeap this condense re-freezing is what's got me. And I think it's also blown in snow, we've had bad drifts too.

Anyone on forums advocating for drilling bigger or more drainage holes?

[svacko]

Yes, I've experienced a few poeple drilling the additional drainage holes on the bottom of the outdoor unit, when they experienced similar problems not having a "nordic" unit. With the nordic unit I mean the features mentioned above - heated compressor and the heating condenser vane.

Though, if it's snow blowing directly inside then I think creating some barrier or add additional shielding of the outdoor unit is required,so that you minimize the chance of the snow DDoS-ing the unit (note: check your unit's service manual for the minimum free distances from all sides of the unit, especially the front one that is the most important to be kept enough free space).