Hey all,

We have a Vaillant ecoTEC plus 831.

A couple of days ago my condensate froze over.  Annoying, but no biggie and a couple of buckets of warm water later it was working again.  I also noticed that the pressure relief pipe had a decent amount of ice under it, but didn't think anything of it at the time.

This morning the boiler turned off (halfway through my shower  ) and it's now reporting F22 - Dry Fire.  Checked the pressure and it's down to 0.3 bar.  Had a hunt around the house and I can't see any leaks.  I attempt to repressurise the boiler using the refill pipes and... nothing happens.  No sound of water flowing, just silence.  I bleed a couple of downstairs radiators and nothing happens.  I've checked the expansion vessel and there's definitely air in there - although I've got no way of checking the pressure on it.

Any thoughts?

You should hear a flow of water as you fill, and the needle possibly spasm.