I got home from work today and my package had arrived from H & G (surprised? not as much as I was!).
Enough Maris Otter to brew.
My wife disappeared to Cribbs Causeway (big mall at Bristol) and left me and #2 child at home.
I got the mash water on, weighed the grain and got everything ready as normal. Put the mash on and went to get #1 child from school. So far so good.
Added the first batch of sparge water to the mash and gave it a good stir. While it settled I put the boiler under the tap.
I ran off three jugs of first runnings and let the clear wort run into the boiler.
At this point I took the childrens tea into them and spent a couple of minutes sorting them out.
On my return to the kitchen I saw a large brown puddle covering most of the floor, the source being the OPEN boiler tap.
I don't know how much I lost, I attempted to compensate on the second sparge but it was all lovely first sparge I lost.
At the end of the boil I was 3 litres and about 8 gravity points short.
It won't happen again
always lock children in the cupboard under the stairs when you are brewing 
I've done it twice 
