Powerflex 50gal gas water heater, 6 years old.
Noticed no hot water, dummy light flashing 3 times = TCO or pressure switch stuck open.

No problem, done this before, pulled the vac tube to blow it out, pulled the nipple and cleaned it out, checked vent, no obstructions. Still same issue.
Replaced the pressure switch, still same issue.
Pulled the vent pipe off, hooked my leaf blower up to it and let it rip. Outside air is coming out of the vent as you would expect with the force of a blower.
Hooked it back up, same issue.
If I run it with the vent disconnected... it clears the self check and fires, so I don't think it is an intake issue. As soon as I put the vent back on it dies.

The PVC vent runs 40' across the house and has a screen on it, and clearly worked this morning bc last night's flurries are melted around it. What am I missing???

You say everything works fine when unhooked from the vent, no issues, etc., but once you hook it back up to vent it fails.

Possibly the vent screen is icing up, vent screen holes are too small, or pipe pitch/length issue preventing good air flow. Just a thought.

Imo, gotta be something to do with the vent. Try running it with the vent screen off and see what happens.

 

Post a couple pictures of the vent from the outside. thank you.

 

 

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Thanks for the pictures.

Screen looks good to me. Nice size holes, I don't see any problems from outside. You can try running it without the screen and see if it makes a difference. Probably not, I'm guessing.

Do you have access to the 40 foot run? Check the full run of the pipe. Post some pictures of that if you can. Maybe a support came loose or something changing the pitch of the pipe.

 

A dip in the pipe so it is holding water in the middle, air under pressure might just move it enough but not clear it?

 

No dips, leaves the heater up to a 90* elbow horizontal and runs 40’ to exit the house. That’s why I put the blower on it, hoping it was that simple.
Can blowers slow down? Maybe it just doesn’t have the power it used to against the friction of the long run?

 

The ceiling is open, I can see the entire run. I am perplexed!

 

With it put back together, have you felt the exhaust airflow while the blower is starting up. Guessing there's an obstruction that's causing back pressuer.

 

Check the installation specs for your specific unit. Some direct vent furnaces, for example, allow 45 ft. max run, but deduct 5 ft. for each elbow. That angled exit of yours also counts as an elbow.
If this is the case, you could be at the ragged edge of max allowable run, and your blower might have gotten weaker, or your pressure switch has gotten weaker.

 

You may be onto it right here. Book says (for my sized unit) 50’ + termination elbow, add 5’ for 90*, add 2.5’ for 45*. By that calculation we’re every bit of 50’.
Looked again last night and see they couldn't go straight out the rim joist as it runs perpendicular. So they 45'd for height, added 4' to the run, and then out. Using 2 45's saved 5' of length restriction. Not sure what I can do here... remove the 90 above the unit and replace with 2 45's (prob not enough change), increase to 3" (equally hard with that turn at the end), or replace the blower and get 5 stressed years out of it and do it all again.

Other ideas?

If I go to 3" it increases my max length to 125', which I could then go all the way to the wall, use a 90* up and a 90* out, and not care about the length they saved by using 2 45's?

.

 

You could just replace the easy part - (the entire straight section of 2" pipe) - with 3" pipe. Use reducers to adapt from 2" to 3" and 3" to 2" and call it a day.
You should save enough pressure drop to have plenty of margin.

 

Good call, keep it simple; I could get a good 30' of 3" pipe on there and then reduce it right at the end.

Begs the question why they didn't just go 25' out of the back of the house, running within the joists. Combustible air intakes go that way as well as the sump discharge. If I go that way I may just do it in 3" anyway and never deal with this again.

 

Rat out the plumber, when all else fails.