Rheem 21VP50 Power Vented Water Heater

[briegg]

Help...My water heater is intermittently failing - and I can't diagnose the problem

When I realize the thing isn't working, the power vent fan is running without the burner on.  I cycle the power off and then back on to initiate the 3 tries to ignite the burner

here are the things I have witnessed when I turn the power off and back on:

1. a few clicking noises.  My guess is that one is coming from the controller (not as loud), calling for the gas valve to open.  Then, multiple louder clicks, and no ignition.

2. only the softer click (again, I'm guessing coming from the controller), followed by nothing form the gas valve, and no ignition

3. the softer click, followed by a louder click, the burner ignitess for a small period of time, and then goes out (between 2 and 40 sec), to the sound of another click

4. successful ignition that stays lit until the water is hot.

The odd thing that I notice is that when I disconnect the leads to the pressure switch, scrape them a bit with a screwdriver, and reconnect them, I have a higher rate of successfully getting the heater to light.

I replaced the pressure switch (~$25 - it was worth a shot), that may have improved things a bit for a while, but now it's going downhill again.  The new switch came with 2 new leads - I replaced the one between the controller and the switch, but the other one that runs into a box with a cover is hard wired to a little plastic enclosure, so it doesn't seem replaceable.

The heater is about 13yrs old, so I don't want to put much into it before considering replacement (I assume the expected life is less than 20 yrs), but if there is an easy, cheap fix, I'd love to try it.

Thanks in advance.

[ROBBYRIG]

It's very possible that the inducer motor is not pulling enough air to close the pressure switch.

[briegg]

Is there an inducer on a water heater?  If so, would you have any insight as to where that animal might be on this unit and how to test it?  Also, if this is not the best place for a water heater question - I'll re-post it in the correct forum - I was a little unsure of where to post, but my water heater is near my furnace, and it makes things hot.

[Bobice]

Your heater : http://homeappliance.manualsonline.com/mdownloads/f918341a-6e8e-41b4-85be-5cde688317b9.pdf

[Bobice]

[user=34365]ROBBYRIG[/user] wrote:

It's very possible that the inducer motor is not pulling enough air to close the pressure switch.

This is not DSI, no inducer motor.

[Bobice]

[align=center]STANDING PILOT IGNITION[/align]  

 

 

The thermocouple is the pilot's, well, co-pilot! It is the electronic device that senses if the pilot flame is hot enough to sustain burning the gas fuel from the burner. If the thermocouple thinks it's safe, then it keeps open the main gas valve located in the pilot assembly. If the thermocouple does not sense enough heat from the pilot flame (such as when the pilot is out), then the thermocouple shuts off the gas valve to the burners.

How the Thermocouple Works

So what is this thing and how does it work? Well the thermocouple (technically called a thermocouple junction) is a device that contains two metal wires welded at the ends and placed inside a protective metal case. The thermocouple sensor is found at the business end of the pilot flame and is designed to be placed in the hottest part of the flame. The other end is connected to the pilot valve body. As the thermocouple heats up, it produces a small amount of electricity and when it gets hot enough from the pilot, send a signal to open the gas valve by using a solenoid operated by a 24 volt transformer. The thermocouple calls the shots, and by converting heat to an electrical signal, it allows the gas valve to open or close.

Once the gas valve is open, gas is then constantly supplied to the pilot and as required for the gas burners (as called for by the thermostat). If the pilot goes out, then the thermocouple gets cold and produces no electric signal to open the gas valve's solenoid and the gas valve shuts off the gas supply to the pilot and burners.

Re-Lighting a Pilot: PREPARATION  

The steps involved can vary slightly depending on your furnace model and pilot valve type, so if possible try and find the instructions inside the furnace door cover or in the instruction manual. Two of the most common types of pilot valve body assemblies either have a red reset button and a gas valve or no reset button and a valve knob that can be depressed. But whichever type you've got, if you have an older model furnace with a standing pilot (flame is lit all the time) then this is the basic procedure.

• Turn you thermostat to 80 degrees or to a setting that will demand heat. Make sure the thermostat is in "Heat" mode.Go to the furnace and find the pilot valve. The pilot valve body is a box shaped device into which the main gas line will run and is located near the gas burners. It will usually have a gas cock or valve knob that reads "On, "Pilot" and "Off." Locate this gas cock or knob.Turn the knob or gas cock to the "Off" position and wait about 3 minutes for any residual gas to clear away.Find the pilot. It's located near the gas burner tube assembly in the furnace.Get your match or lighter ready. Sometimes the pilot is hard to reach. If possible, try and use a long fireplace match when you light it. If you don't have a fireplace match then a butane BBQ grill lighter works well too. If you don't have that, then you can fasten a match to the end of a stick when you light the pilot.

Re-Lighting a Pilot: IGNITION
To actually light the pilot proceed as follows:

• If you have a pilot with a red Reset button, turn the gas valve from "Off," to "Pilot."If you have a pilot with no red button, turn the knob from "Off" to "Pilot."Place the lit match or ignited lighter tip at the pilot and depress and hold the button or depress the knob as appropriate. Depress the button or knob for about 30 seconds. This maintains gas flow to the pilot until the thermocouple gets hot enough to open the main gas valve.Once the pilot stays lit, slowly release the button or knob and turn the gas cock or knob from the "Pilot" position to the "On" position. This will ignite the burners and keep the flow of gas supplied as required for the burners as called for by the thermostat.If the burners fail to ignite then it may be because the thermocouple did not get hot enough to open the gas valve. Wait a few minutes and then repeat the above procedure. This time hold the red reset button or depress the knob for about 45-60 seconds.Once the main furnace burners ignite, adjust the thermostat to the desired setting.

When the Pilot Won't Stay Lit

If you've followed the previous steps on lighting the pilot and it still does not light after, or will not stay lit, then you probably have a problem with the thermocouple or an adjustment needs to be made to the pilot.

 

Pilot Has a Weak or Irregular Flame

If the pilot lights but the flame is a weak yellow flame, it will not get hot enough to heat the thermocouple to its set point allowing the gas valve to open.

A natural gas flame should be a bright blue with the tip of the flame having just a tinge of yellow. A propane flame should have a bluish green flame with a tinge of yellow at the tip. The flame should be strong enough to hit the thermocouple tip about 1/2 inch from the tip end. If the flame is weak or shaky looking, check to see that a breeze or draft is not blowing on it.

Adjusting the Flame

There is usually a small screw on the pilot valve body that will adjust the flame. You may have to refer to the manufacturer's instructions to find the screw. Turn the screw as needed to adjust the flame throw.

Yellow Flame

A yellow flame is caused by lack of air and incomplete combustion. It can be caused by a dirty pilot tube tip.

Split Flame

This is caused by dirt in the pilot tube. Take a needle or small nail and gently clean the tube.

Flickering or Wavering Flame

A flame that flickers is usually caused by a draft.

START-UP AND CHECKOUT Adjust Pilot Flame

The pilot flame should envelop 3/8 to 1/2 in. (10 to 13 mm) of

the thermocouple/thermopile tip. To adjust the

pilot flame:

1. Remove the pilot adjustment cover screw.

2. Turn the inner pilot adjustment screw clockwise  to decrease, or counterclockwise

to increase the pilot flame.

3. Always replace the pilot adjustment cover screw and tighten firmly after completing adjustment to ensure

proper operation.

 

[briegg]

Wow - I appreciate the time you must have spent Bobice.  Unfortunately, this does not resemble my water heater.  The Rheem 21VP50 is a power vented model with a hot surface igniter (no pilot flame that burns constantly).  I think the problem is either the controller (a Robert Shaw), the Gas valve, or some sort of obstruction in the vent.  Really, I'd like some help in ruling out the first two to see if I need to disassemble the piping, which would be a huge task.

Any help anyone could provide would be much appreciated.

[Bobice]

http://waterheating.rheem.com/content/resources/documents/tech%20bulletins/1600%20Series/1602.pdf Does this help ?

[Bobice]

Is this a "Guardian Unit" ?

[briegg]

I don't think this is a Guardian unit - when I look on the Rheem website, it seems like those are newer - the controller in the technical bulletin you sent is different from mine (mine is a Robert Shaw - this one is a Honeywell).  The unit I have is at least 13 years old (the original unit installed in a 13 year old home). 

 

The model # is 21VP50-1.

 

Thanks again Bobice for your help - I'm still not sure how to diagnose if it's a controller or Gas valve problem (or anything else for that matter).

[Bobice]

Try this : http://waterheating.rheem.com/content/resources/documents/tech%20bulletins/1600%20Series/1604.pdf

[Bobice]

Robertshaw Controler :http://waterheating.rheem.com/content/resources/documents/tech%20bulletins/1600%20Series/1603.pdf

[ROBBYRIG]

My eyes aren't as good as Reg's but I'm pretty sure I see a blower motor there in that link you just posted.

[Bobice]

My fault. The first manual was a 21 VG50 standing pilot . Need my glasses .

[RegUS_PatOff]

ROBBYRIG wrote:

My eyes aren't as good as Reg's but I'm pretty sure I see a blower motor there in that link you just posted.

Bobice wrote:

My fault. The first manual was a 21 VG50 standing pilot . Need my glasses .

:ooo:  see RegUS_PatOff

[Bobice]

Scewy Wabbit.