Have a new as3 b2l installed by builder but they are offering no assistance. Unit tries but does not ignite. Error code 12a. Where can I find installation instructions for this heater?

The technical, fault code and installation documents for your Eberspacher S3 B2L Airtronic heater can be found at https://www.butlertechnik.com/technical-library/s3-d2l-b2l-airtronic. The error code 12a refers to " Unsuccessful starting process" and the manual instructs to do the following - "1. Check exhaust and combustion air system. 2. Check fuel quantity and fuel supply. 3. Check the fuel filter or fuel strainer in the fuel metering pump and renew if necessary. If you require further technical assistance please email sales@butlertechnik.com or call +44 (0)1522243310 and our experienced staff will be happy to assist.