Hi all, got called out to connect a cooker and chap mentions his worcester 24 cdi getting DHW but no heating. One od the old ones where you can't see the plate HE. It works OK if you press the reset button, stays on, doesn't cut out etc, but won't fire up, cold or hot, on its own. DHW fires up no prob. End of a Saturday, so I told him I'd look into it another day, and maybe to live with it for the life of the boiler, false economy etc. Any ideas?