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Experience:  25 years in the trade. new Construction, remodeling, repairs ect. Business owner. 2nd gen plumber
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I have a Rheem 21vp40e power vent water heater. it stopped

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I have a Rheem 21vp40e power vent water heater. it stopped heating and when checking it out I noticed the control module smelled burned up so I replaced the module. All of the wiring is correct but I still get no spark at the igniter. The puge fan runs but nothing else happens. I have 29 volts at the input and output sides of the vacuum switch. I have that voltage at the control module but there is no voltage reading at the MV PV ETC. ports. I'm baffled at what is wrong with this water heater.
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sounds like to me the mother board is fried , i see this a lot, then you go and replace the control module but it doesn't fix the problem because the hole thing got fried, this can happen due to product failure or a power outage and power surge.

Hi, I can answer your question, lets handle them one at a time. Click 'accept' when you are satisfied.or we can getanother expert.


The ignition module is likely bad. check voltage to that during the ignition phase and tell me what reading you get...we can go from there. Phil


Customer: replied 6 years ago.
I have 29 volts to that during start up. I just put the new control module in the unit because the other one smelled burnt up when I checked it so I replaced it and it still doesn't work.
Customer: replied 6 years ago.
Relist: Incomplete answer.
Do you have 29 volts in put and output of fan vac switch with the fan off? Just checking to see if the vac switch is stuck. If not I need to know if your model has a spark ignition, or hot surface igniter
Customer: replied 6 years ago.
I will have to re-check that but I think it is working correctly because I hear the switch click when I power up the unit. This unit has a spark ignition.
Ok, Just let me know. Ill take it that everything is working as it should be at this point.

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Customer: replied 6 years ago.
I do not have output voltage at the switch with the fan off and the unit has spark ignition.
Is it working? If not, Is it spraking? and if so Is the pilot lit? Reason I am asking is to see if the flame rectification (pilot sensor) is working. Alot of times the pilot will lite and the unit will keep sparking (trying to lite) because the sensor isn't telling the unit the pilots lit. At that point, If its sparking, and not lit, check for voltage at the gas valve terminal across pv & mv/pv the MV/PV is the common.
Customer: replied 6 years ago.
It is not sparking at all. Before the unit stopped working my kids heard the unit rapidly clicking when I was at work. I assume this was the ignitor sparking. This was during the night before the unit stopped heating. My wife called me the next morning at work to tell me we had no hot water and when I got home and checked it out is when I noticed the module was burnt out. After installing the new module I haven't heard it attempt to spark at all.
If there is no voltage to the blue and white that means the control module is malfunctioning, as a previous expert mentioned. I know its new, but its an electronic part and they can be bad right out of the box. Basically, when the heater goes in to "call for heat" the thermostat will send voltage to the module and it will have to be proved through the vac/blower switch. You already said that was working. Did you by chance do a continuity test just to make sure? I know its redundant, but. Ok after the voltage goes through the switch, the module send spark to the igniter and 24 volt signal to the gas valve. Flame sensor picks up pilot and module open gas valve. simple

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. One thing Id like you to try, With a pair of insulated pliers, pull the ignition wire of the module and hold it about a sixteenth of an inch away from the terminal and turn the heater on. If it jumps spark from the pole on the module to the plug, the pilot assembly needs to be cleaned and or replaced. If you would like a copy/link to the manual, I have can it and can upload it for you.

Edited by Pitsch Plumbing on 10/6/2010 at 3:05 PM EST
Customer: replied 6 years ago.
I tried the spark test and no luck with spark. I guess I will have to go get another control module and try it. I suppose I will have to eat the money on that one because most places don't take returns on electrical components and if that's the case I will be out $195.00. If you would please upload the manual for me that would be great and I appreciate all of your help. Thanks, Rick

Here is the link. Also, before you replace the module, unplug the PV and MV (blue and red) and see if it sparks. also, Double check you ground wire. That could also be a reason for the box not responding. If none of that works and you get a new box, try it without the gas valve plugged in. Fortunately in this case your model is probably one of the simplest Power vents (wire and control wise) they made. new ones have become extremely complicated. Here's the link:


My reason for trying it without the gas valve plugged in is just incase the valve is shorting internally.





Edited by Pitsch Plumbing on 10/6/2010 at 5:09 PM EST
Customer: replied 6 years ago.
Hi, I made sure there was a good ground connection and i diconnected the wires to the gas valve like you suggested but still no luck. This replacement Honeywell S8610U module says it has LED trouble codes built in. Should any of these be showing because there is no LED display at all showing up. I guess I may as well stop tomorrow and see if they will exchange this module.
It has and led near the wire terminals. Make sure the oem box and the new one match part number wise.

ohh, and here:


Thats pretty much all of the 8600 series ignition controls. Last thing, if your module has ground and 24 volt ground, connect them both. See page 5.

Customer: replied 6 years ago.
One last thing, should an led be lit up when it is powered up?
Page 12 of the PDF shows you the LED cycles. If there is NO led, It says no call for heat, but since you do have voltage to the box and the wiring is correct, The module most not be registering call for heat.
Pitsch Plumbing, State Certified Plumbing Contractor
Category: Plumbing
Satisfied Customers: 370
Experience: 25 years in the trade. new Construction, remodeling, repairs ect. Business owner. 2nd gen plumber
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