Tom,
Stay well away from this man only contact him through your Solicitor, no telephone calls to or from him and warn your brother and anyone else involved on the job to avoid that post code to the point of everyone keeping a daily diary.
Not only will he have your heating system and outstanding money he could have your Freedom.
Forget the macho bull this is business you are up against one of life's scum whatever you do don't try playing his game, the rules he plays by are completely different to anything decent people are used to, he knows you are wounded and is now trying to rub salt in looking for the reaction that will guarantee him a free heating system plus the chance for compensation.
Try to stay calm, hand the job over to the professionals and get on with your business and private life.
Scum like this can eat away at you from the inside without ever being physically near you.