Water Heater Help

[ichorniy]

I have a Rheem Classic heater model: PRO G50S 36N CN67 PV.

It has a sensor that is supposed to monitor exost. After buying a house heater, it went into error mode with 3 blinking lights, so I replaced the sensor. It helped, but every winter in cold weather, usually -10 or below, the same 3 blink would come up. I snaked the exost pipe from one end to the other with no blockages. If it's getting really costly, the heater goes into error almost every hour. I need to wait before restarting, it will work for an hour or two hours and shut off again. Sometimes it would not even last 30 minutes. In summer, no problem, the heater works like a champ.

Any suggestions on what could be causing it, and especially why cold is a factor?

If sensor was replaced should i look at fan replacemetn etc?

[Admin]

Are you able to post a picture of the gas control that displays the 3 flash error code?  And a picture of the switch you replaced would help.  Have you verified there is no ice built up on the outdoor vent termination?

I suspect this may be a pressure switch issue.  It's possible during colder weather there's more condensation building up in the venting.  If the venting isn't sloped properly this water could be a restriction causing the pressure switch to stay open.