blower pressure switch trouble

[russ1]

I have an A O Smith 40 gal water heater power vent,
The fan comes on but then I get an error code that pressure switch is not closing. I have jumped that switch and the burner starts up just fine. I have blown out the exhaust so there is no blockage. I have sucked on the switch hose and this closes the contacts, checked this using an ohm meter. I also bought a new switch and is working fine. I have also blown out the barbed brass fitting that comes out of the blower to make sure that is clear and replaced the hose. The fan seems to blow with plenty of power. All I can think of is that the fan blower is not running fast enough to create enough vacuum to close the switch or am I missing something? Any help would be appreciated!
Thanks

 

[Diehard]

I looked for any info that would help trouble shot your problem but came up empty. Lots about testing the switch, as you already have. But nothing relative to verifying the adequacy of the fan.
I would call A O Smith factory engineers and ask them.

I did find this Tech Bulletin...

 

[Rickyman]

Disconnect the vent and try to run the heater. If it operates normal you have a partially blocked vent. If it doesn’t work, check the combustion inlet of the heater for a blockage. Also make sure there’s no holes in the rubber tube to the pressure switch and it seals tight.

 

[SHEPLMBR]

Is in in a room with good airflow?

 

[russ1]

Thanks for the replies, I'll try taking the stack off and blowing out the inlet and yes it has good air flow the heater is about 10 years old and was working fine

I have an A O Smith 40 gal water heater power vent,
The fan comes on but then I get an error code that pressure switch is not closing. I have jumped that switch and the burner starts up just fine. I have blown out the exhaust so there is no blockage. I have sucked on the switch hose and this closes the contacts, checked this using an ohm meter. I also bought a new switch and is working fine. I have also blown out the barbed brass fitting that comes out of the blower to make sure that is clear and replaced the hose. The fan seems to blow with plenty of power. All I can think of is that the fan blower is not running fast enough to create enough vacuum to close the switch or am I missing something? Any help would be appreciated!
Thanks

 

[RenewDave]

Clean the fan itself. These motors are very low amprage, so if the fan blades get oily or dirty they weigh more. The resistance put on the motor to overcome the added weight can through that error code. It sounds crazy but I have fixed a bunch of tankless error codes by cleaning fan blades.

 

[russ1]

I looked for any info that would help trouble shot your problem but came up empty. Lots about testing the switch, as you already have. But nothing relative to verifying the adequacy of the fan.
I would call A O Smith factory engineers and ask them.

I did find this Tech Bulletin...

I looked for any info that would help trouble shot your problem but came up empty. Lots about testing the switch, as you already have. But nothing relative to verifying the adequacy of the fan.
I would call A O Smith factory engineers and ask them.

I did find this Tech Bulletin...

Clean the fan itself. These motors are very low amprage, so if the fan blades get oily or dirty they weigh more. The resistance put on the motor to overcome the added weight can through that error code. It sounds crazy but I have fixed a bunch of tankless error codes by cleaning fan blades.

Thank you I'll give it a try !!!

 

[russ1]

Thank you I'll give it a try !!!
Got it fixed. I removed the exhaust pipe like u guys said heard a definite change in fan speed. So I checked the owner manual it it showed that the exhaust pipe cannot be reduced until after the first elbow. The goofball that installed this 10 years ago only put a 6 inch lenght exhaist pipe coming out of the blower then reduced to 2 inches right away. There must have been to much restriction in the line. Vacuum meter showed it was hoo wring right around in .75 in water column so it would close properly.
Thanks again for your help!!