In reply to captain paranoia:
> Does the burner appear to be weak, even when the valve is fully open?
Yes
> Have you made sure you're screwing the canister on fully?
Yep, hard as sensible
>Check the little prong that opens the Lindall valve on the canister. If it's not long enough, or is damaged, it may not be opening the canister valve properly.
Might be a silly question, but how do I check how long it is meant to be?