more chilli growing expert advice needed!

I've grown some Hungarian Wax this year in the polytunnel, and to be honest I was going to pull them out, as they didn't appear to be doing anything up until about 5 weeks ago.  However, they put on some growth, flowered, and have now started to crop.

Soooo....I've harvested/used about 10 so far, and to be honest, they've been PATHETIC!!! I've eaten hotter cucumbers!! HOWEVER - I picked 4 tonight, and lobbed three of them in the massive pan of "I Grew It So I'm Dam'n Well Going To Eat It" stew type thingy I made tonight, which I will freeze, and chopped the other one into the salad I had for dinner (lobster - the only thing I didn't grow, but caught by a mate off his boat so still local!)  Of course, the huge error, which all you experts will have spotted, is that I haven't mentioned tasting any of the chillis before adding to recipes.  And yes - the one on the salad has got the same capabilities as a medium range thermo nuclear device, so I am just a little wary about trying the stew and seeing how many layers of taste-buds it will remove. 

So, finally getting to the point - what happened?  Why the change in heat, from 3 days ago to now? Is this usual for chillis to change heat?  Is it all a big laugh in the chilli plant community to lull novice growers into a false sense of "I'm oh-so-bland...go on rascal, BITE ME!"  security?  Please help, as now I'm scared.....

hmmm....it's been scorchio here for a couple of days, so maybe that is it.  I'll just have to VERY CAREFULLY try before using from now on!

thanks for the advice, both of you, and I'll try the recipe suggestion, Lardman, although I'm still nervous!