1991 Rheem 40gal LP not heating

Hello,
I have a 1991 Rheem 40gal LP W/H Model 21VP40 1/P-A which decided to not heat water this AM.
The Power Vent is on (exhaust) and the electric Pilot Ignitor cycles on and off because there is no ignition of the gas. It seems to me that there is no gas to ignite as I believe the valve is not turning on. (No smell anyway). There is gas to the heater and the valve is turned on. (The furnace works as well). How do I determine whether the problem is a faulty Gas Valve, Ignition Control Module or other?
Thank You!

 

Contact the manufacture in regards to this unit; it sounds like it is trying to lockout, could be numerous things that are causing this problem.



They will know how to troubleshoot your situation, short of giving you an authorized rep in your area that knows your specific unit.


If it was an A.O. Smith, I could better help you with your situation.

 

For anyone else having this problem it turns out to be the gas valve gone bad. How this works: The PowerVent fan goes on 1st, which creates vacuum down a tube to a diaphragm which triggers a switch, signaling the controller to start the igniter glowing. When glowing at max the controller tells the gas valve to turn on. The gas valve turns on, and the gas is lighted. Well the gas valve wouldn't listen anymore - it was shot and in need of replacement.

 

Ouch. That sounds like that was fairly expensive.



With some of the newer models there is a flashing LED light that will flash in sequence; the sequence depending on how many flashes in series will tell you exactly what is going on with the unit.



I usually farm these kind of jobs out to techs who deal only with powervents, just like many other plumbers in my area. Too expensive to keep inventory for those units and too much time involved in troubleshooting.


Some things are just better done by someone who works on them exclusively.

 

I also had the same problem, the water heater vent motor was running with no burner flame ... we would do the reset (turn off the gas and motor, wait, then turn on the gas then the motor) and the burner would lite ... this first happened just once in a while then it seemed every week, then ever day and finally the burner would only lite sometimes ... I first thought the issue was the gas valve because I can see the ignitor on, I just wasn't getting any gas to ignite ... I am fortunate that I have two identical water heaters so it was easy to change the ignition module -- go figure the module was bad keeping the lockout engaged ... the module is a Robertshaw HS780 17NL-104A which lists for $179.95 on the internet ... called the local jobber here (PenCo) and they had an HS780 34PL-308A for $59.95 ... their book shows it as a direct replacement for the 104A ... water heater works like a charm now ...