Rheem Power Vent Mod# 21VP50-1P acting strange....

[ornrydaddy]

I was working in the utility room last night when I noticed my Rheem Power Vent water heater was acting strange.  I could hear the fan motor running as it normally does during the heating cycle but the flame kept turning on and off until the thermostate quit calling for heat.

During the call for heat from the thermostat, the glow plug came on and then the gas valve would open shortly thereafter to ingite the flame.  The flame would burn for about 30 seconds or so and then suddenly stop with a click (I think the gas valve closed).  Then almost as soon as the flame went out, the glow plug would come back on and then and with another click from the gas valve the flame would reignite.  This cycle continued until the thermostat stopped calling for heat.

The unit is still making hot water (thankfully) but I'm fearful that the over cycling will cause a premature failure of control components.  I had to replace the gas valve about 2 years ago and replaced the control module last October.

I suspect there is a temperature sencor somewhere that needs replaced.... any help or information would be appreciated.

Thanks,

Eric

[forestone]

Try cleaning off the thermocouple and the flame sensor (since you'll be in that a same area) with steel wool. Remove them from the framework to clean them properly. They're usually held in place by a single screw or snap in place by a mounting clip. Be careful not to brush up against the hot surface ignition device (glow plug); they are brittle and the way some are designed, an "arm" could snap off if caught or bumped by a tool, or handled roughly. (That's right, I can learn from my mistakes)

If that doesn't do the trick, then replace the thermocouple (first), then the flame sensor (second, if the thermocouple repl didnt't solve the problem).

Applianceman has an excellent video demonstrating this in the HVAC forum and here's the link--http://applianceguru.com/forum13/22527.html

Good luck. If you still have the same symptoms after doing this than the next step is to look at the draft inducer system and its vacuum/end switch(es). The good news is that you've already replaced the most expensive parts of your heater, so everything should be gravy from this point.

Steve

[ornrydaddy]

Thanks for the tip.

As it turned out, I ended up replacing the glow plug.  It turns out that this unit doubles as a hot surface igniter as well as a flame sensor.  Once it was replaced the unit works as normal!

[forestone]

You're welcome. That's great. What I wasn't paying attention to is that your heating device is a water heater not a forced air furnace because I got all excited with my first post. However, like all gas heating devices, they have common components and problems like intermittant call-for-heat cycling. This is why simple things (and inexpensive) procedures like regular cleaning of thermocouples/thermopiles, flame sensors, and filter replacements; are so effective at keeping your heating equipment humming smoothly.