Navien CH-240 fan won't stop and constant "Abnormal air pressure" errors

mungbeans

I've got a 3 year old Navien CH-240 boiler which has started displaying an "Abnormal air pressure" error with increasing frequency. It was every few months, then every few weeks, now its happening every couple of days, or every few hours sometimes.

The supposed cause of this error is if there is a blockage in the air flow - but the air pipe leading from outside the house into the boiler is clear, and the air filter is clean. So I don't believe a blocked air flow is the cause despite what the error says.

I've also noticed the fan stays on for ages. If I turn on a hot tap, then the boiler springs into life, then if I turn the tap off the boiler part itself stops (the gas flames stop) but the fan keeps on making a noise for 5 or 10 minutes or longer, and sometimes its spinning crazy fast.

Has anybody encountered this sort of behavior, in general or with Navien in particular? Could the fan itself be broken, or is it more likely to be the electronic circuitry controlling it?

Is there anything I can do myself or am I going to have to call a repairman to come and take a look at it?

Thanks in advance for any replies

Jamie Hall

Double check both the complete intake and exhaust ducting, and all filters. Both the error message and the fan behaviour which you describe sound like blocked or partly blocked air flow.