Vic afloat

Hi, I am hoping someone can help. We have a Webasto thermo pro 90 on our narrowboat. It has a fault. We have completed the re-set and seem to have got round the lockout problem. It now shows fault code 16, exhaust temperature fault. Any ideas or tips on what could be causing this, or how to fix it? Also, when we ave checked everything else, there is a leaky valve leaking the coolant/water from the webasto under the bed. Bit messy and can't seem to tighten it. I feel an engineer call out might be needed, but am asking here first. Thanks in advance, Vic