Yes, that clears it up a bit. I should spend more time trying to figure out the groupings.....
Yes, the vocab wasn't the problem. Waermepumpen is practically English and trock

- has/had an English cognate that slips my mind.
Then you can go the other way which is way more complicated to write than to do in your head:
d=t, especially when the next letter is r.
ck ~= ch ~= gh. And gh in English tended to disappear when it was the last phoneme in a root.
So we're left with "What's an English word that fits this situation and consists of d/t + r + random vowel* ?"
Oh, 'dry'.
Does this work all the time? Hell no. But when you're trying to figure out something within a specific context and you know the part of speech it has to be and you know some of the more likely sound/spelling mutations between the two languages AND you have nothing else, it works way, way better than random chance.
*Random vowel thanks to the Great Vowel Shift. It's the one area of English language history that makes my eyes glaze over in 3 seconds flat. No, really. I'd rather go to a 6 hour seminar on strong verb declensions than a 1 hour seminar on the Great Vowel Shift.