buderus wall-hung won't fire

I have a Buderus GB-142, installed about a year and a half ago. Thanksgiving morning, it was reading error code 6A, which means it tried to fire 3 times and then gave up. Turning the power off and back on reset the system and solved the problem for the time being.
Today, it's off again. Now, the boiler makes this gurgling noise, as if there's air in the system, while it tries to fire. After 3 tries, it kicks out again.
So, while I'm waiting for the plumber who installed the system to answer his pager, I wonder if you can help a poor electrician diagnose this problem.
Pressure reads 20psi
I'm thinking I should purge it somehow, but do I need to drain the whole system? It's radiant plus dhw.
Thanks for any advice.

no heat; help!

House temperature is dropping through the 50's; any help appreciated.

problem solved; condensate vent was blocked

What was blocked the condensate line or the vent it self ? I would have mentioned that it won't fire if the vent was blocked but I have ben busy in my basement installing a new GB142. how do you like it ?

Lou