Outdoor wood boiler airflow question

Hello, please delete if wood boiler questions are not allowed in the woodstove subreddit. I’m just in need of some help.

I’m in a cabin that has a Central Boiler eclassic 2400. Unit was installed in 2010. I am new to the property and this is my first year running it.

Fired it up for the first time yesterday and everything went great. Got a fire going, started to get some coals. Water got up to 185° and all was good. Had it going from 10am to 10pm when I loaded up some logs and then went to sleep.

Woke up this morning and house was cold. Boiler water temp got down to 140. On attempt to reignite the coals, I got them glowing red and had a good bit of wood burning.

Problem is as soon as I close the door, the temp drops and it wont stay hot. Even if I get the firebox up to 450° before closing the door, as soon as I shut it, temp drops. This is an airflow issue right?

Puzzled because I checked owners manual and cleared out all the ash from the air intakes inside the firebox. Problem still persists. Not sure what to check next. Sorry for not being more informative but I’m new to this.

If there is any additional info I can provide to help please let me know.