"Air Pressure" fault on Baxi Luna 1.310 Fi

DouglasEWilliams

I have a Luna 1.310Fi boiler for radiant heating only. It is natural gas fired and located inside the house with a concentric air duct inside the flue duct going a few inches to the outside. The unit has worked for years, although I did replace the pump a few years ago.

It recently stopped working. After a reset, sometimes it will fire up and get to its operating temperature, but then it stops at some point with an "Air Pressure" error.

Per the manual, I've checked the electrical and pressure tube connections; blockage of pressure tubes; restriction in flue; and venturi, with nothing problematic on any. I replaced the pressure switch, even though it seemed to be ok, same issue. I then replaced the fan with the same result.

On this unit, the pressure switch has hoses going to a venturi and air outside the cabinet, and all are clear.

I've run out of recommendations from the manual and the obvious possibilities and would greatly appreciate any thoughts or insight over what could be the problem and/or how to fix it.

Intplm.

These things can make a guy scratch his head bald figuring them out.
What I have found with these types of units is that they can be very very fragile with their inputs.
Usually, something like this is attributed to a dip switch incorrectly selected. (Did one get inadvertently hit when serviced?)
Is there anything dirty cob web dust etc?
I know. It's an air pressure fault code description you are getting but this could also have been triggered by a low flow from water pressure, low water pressure, or gas pressure.
I've had some codes show up that sent me on a wild goose chase from a description code on the panel that was not what it turned out to be.
I would look at this from square one, with an open mind. And if all else fails its time for a conversation with there companies tech support.

DouglasEWilliams

Thank you for your response. This started happening when the unit was untouched, so I've not looked at incorrect wiring or switch settings. I've had it apart and don't see any evidence of rodents or insects. The water pressure is well above the 0.5bar min, so I haven't pursued that either.

DouglasEWilliams

I cleaned the water pressure differential valve, but didn't replace the diaphragm as it wasn't damaged. This appears to have fixed the "air pressure fault!