JMAC

Thanks all for comments, much appreciated. Just waiting on delivery of a unit now by a supplier who advises that the frost protection sensor which is coupled by a harness to another sensor on the latest models be removed and replaced with old version stand alone sensor. Will be interesting to see how it goes. In answer to some of above, none of the advance models I have seen in the field are connected to a 3-speed switch but the advance plus models are. The Heatrae manual not really of much help, full circuit diagrams would be nice....

Hi, I’m new to concept of forums but thought I’d give it a go. I service MVHR ventilation units and have a particular problem with Heatrae Sadia Advance models. This model has been replaced by the Advance Plus which looks identical but for a clip on cable connection on the fan assembly module. Replacement fan assembly modules for failed units should in theory fit both advance and advance plus units but you need to remove the additional clip on cable to allow the module to physically fit into older advance models. The problem however is that the new fan modules will not work correctly in the older units whether or not you disconnect the cable or leave it connected but uncoupled from the fan module body. Invariably the replacement unit will work briefly but will eventually switch itself over from low speed to boost speed without activation of a switched live signal and will not return to low speed unless you kill the power supply completely. Has anyone else come across this problem. Note, have tried getting advice from Heatrae Sadia and Baxi but they are about as helpful as a proverbial chocolate tea pot. thanks for listening John