Our Ecotec 937 has stopped working this morning. Error Code f81. It was installed and commissioned approx 8 months ago and has been working fine. The installer filled out the required details and signed off the installation. This morning we had no hot water and on checking the boiler noted the error code. I've read past posts on this subject and it seems this model has a known problem concerning the PCB leading to the boiler displaying this code error. Could somebody explain to me what exactly this code means and why the PCB is diagnosed as the culprit? Will a replacement PCB sort this problem? Has this been documented as a final fix or is this error code an ongoing unresolved issue on this model? I'm concerned that if the problem relates to the unvented tanks on this model then the engineer may just bypass this function and claim all is well! Our Vaillant room thermostat has also developed an error code BMU Err which I assume is related? We have an engineer coming out on Weds which means no heating or hot water until then. Thanks Vaillant - nice product!