I came across this during different jobs ive been called out to. it could be a faulty diverter valve (or zone valve). these are silver metal ( or white plastic) boxes located on the pipework usually in the airing cupboard. if they start to leak they will sometimes short circuit and fuse. also, if the central heating pump is faulty this can also cause a fuse to blow. it could even be a simple case of loose wiring in the termination box. ask a Honeywell trained plumber to check these points out.
mark. (oftec engineer), October 2008
