Replaced 50 gallon rheem power vent water heater under house in crawl space in jan 08. Worked fine for 4 mo.?

Question

Then would not stay lit. Replaced heater since under warranty and same problem exist. Changed 2 lb gas regulator at unit. Gas company ran pressure test at outside meter and replaced outside regulator. Now unit will stay lit as long as heat shield is not installed at burner opening. Once shield is installed. Flame ceases and unit shuts down. Unit will recycle shortly aftwards, with fan engaging and pilot activating flame. Once shield is reinstalled, unit fails again. Plenty of room under crawl space. Stand up area. Visible outside foundation ventssurround heater. Gas furnace located in same area with no problem. 3 inch exhaust PVC vent aproximately 45 foot run with proper grade. Any help????????????????

Answer 1

There's an obstruction in the venting system.  Something is blocking the vent either in the pipe or blower.  If the blower is separate from the water heater (didn't get replaced), it is not coming up to speed or the blower wheel is clogged.

Answer 2

Check your installers manual. 45 feet seems a bit longer than I remember being acceptable. You also need to figure 10 Feet for every elbow so this 45 feet could actually figure up as 55 or 75 feet.

I believe there is also a requirement for a minimum 12 or 18 inch straight pipe directly on top of the inducer before the first ell, but I'm not sure. That should also be in the installers guide.

Answer 3

This may be more of a gas pressure issue.

If this is a 2# system there should be another regulator to step down to 7" WC for natural gas and 11"WC for propane before it goes into the appliance.

I would make sure the proper o*****e is installed and the proper manifold pressure is there when running.

It sounds over-fired.

Also that vent length may be exceeding the maximum length. Make sure your including the elbows in determining the maximum length. Check the installation instructions.