aaagghhh: ignition for 8 seconds then relight

[dumbass]

My Baxi maxflow wall mounted combi ignites for upto 8 seconds (both heating and hot water) then goes out but automatically relights, checked thermocouple, glows red hot but tip is black, could this be the problem

Also need to know recommeded psi for expansion vessel. i stupidly let all the air out, dumbass do i need to drain the expansion tank as well before i repressurise it?

Thanks in advance for advice, would get corgi on it but am totally brassic

 

[IanDB]

Re the expansion tank. You have to drain the boiler and then re-pressurise the tank to, normally, 1.0bar. The manual should tell you.