Hi Alex, most probably of no help, but if you set the test switch to overide this will overide the tx if there is a fault on the heat sensor, which would fire it up regardless, but this may be just the transmit side and be independent to the receiver. Are you going to Malvern by the way, will email you as well regarding other items, all the best Ian. p.s will ask a friend about the 353, might be able to throw some light.