I've got a power vent gas water heater that has operated perfectly for several years but lately been unable to shut off without a racket.
The problem seems to occur when there are multiple uses for hot water, i.e. weekends.
The vent fan comes on and off rapidly and the solenoid clicks like a machine gun. I can make the unit "fire up" by running hot water until a definite demand is created. I replaced the thermostat and gas control valve. I've checked the air line and then replaced the air pressure switch. I've had the gas company out to check the pressure which was 7" W.C. so now I'm lost.
Any experts out there?
I have contacted the manufacturer, who tried to help via email but gave up.

Check the vent outside to make sure nothing is blocking it.

Outside opening of vent is clear. Snow melted for 2 foot diameter. I keep thinking it has something to do with the thermostat because it operates fine when there is a strong demand.