Rheem 406A Heater Blowback

[filmsmith]

We have a 25,000 gallon in-ground pool that was rebuilt this summer. During the winter and the idle time a small creature built a nest on the burner tubes of the Rheem 406A propane heater. We cleaned it out and blew other leaves and debris from the heater, but the heater blows back when when we try to light it. Technicians from the pool company replaced the burner tubes and everything appears to be clean and the pilot system seems to be sparking correctly, but it still tries to fire up a couple of times and then eventually ignites and blows back with flames belching out of the bottom access under the burners.

The heater is 10 years old and the technician said it's time for a new heater. I'm concerned that there may be further internal cleaning required, or better alignment of the pilot, but I have not disassembled the manifolds and tubes myself to examine them.

He said everything looks clean and I don't see any obvious rust or corrosion, and the pressure is good from the underground tank. Is there something else I should be looking for - other than a different technician - or is a new heater the logical solution?

 

[ps0303]

Did you clean the heat exchanger of soot? Pop the top and make sure nothing is sitting on top of the heat exchanger. If clean, turn the gas off and remove the burner tray. Then a hose with a fairly strong spray nozzle and spray from the top down and then up from underneath the heat exchanger. Do this several times and if you get lots of black soot, that's probably the issue. Careful, if you get the soot on your clothes they will be done for.

 

[Pool Clown]

When you say "Blow back" are you saying that are getting:
A) an ignition of pooled gas? a whoom?
Or are you getting:
B) A continuous flame coming back up from below the gas valve after an otherwise normal ignition?

If A: I would look at the burner tubes and jets again. Pooling gas suggests a delay in ignition. This can be from a clogged burner tube, usually spider webs, or a clogged jet, maybe two. In particular, the last two on the right. This is where the pilot is. It is critical that those two are clear, so that the heater can fire without incident. If these one or two jets are clogged, it would force the pilot to ignite the gas from the third (or the first clear) rail, causing gas to pool until it migrated to the source of ignition, by then, there would be enough gas accumulated to cause a significant "woosh", if you will, or dare i say, explosion. Sometimes this can be enough expansion to cause the heaters' service panel to achieve flight, and cross the backyard. Early Laars heaters were famous for this.

If B: i would address the sooting issue as Paul stated earlier.

 

[filmsmith]

The blowback seems to be your suggestion "A", a whoom of flame rolling from under the heater. The jets, which I assume are the 22 tubes with the holes for the flames, have all been replaced. I did not inspect the tubes between which these are mounted, but I assumed that the technician would have done that since he pointed out the deterioration in the jets (from rust) that had caused the holes to be of irregular sizes. He first replaced only the two tubes on the right because they had appeared to be severely deteriorated, but when that did not solve the problem he replaced the remaining 20 but that did not solve it either.
He also removed the pilot light assembly and we tested it separately and it appeared to function normally. In an earlier forum entry from last year, the misalignment of the pilot light was listed as one possible cause for this delayed ignition, but I did not consider that when we were attempting the repair.
This problem was first noticed a few weeks ago when we lit the heater following the renovation and it began smoking. We turned it off immediately and dowsed the coils with buckets of water from the pool. The following day I blew it out with a leaf blower to clear any debris, and also hosed it as well as I could could from the top with a pressure nozzle on a garden hose, but when it smoked again, and I sprayed it down again, the renovators called their technician and that is when we discovered the nest on the jets. So while the coils were not deliberately cleaned, they were inadvertently washed quite a bit.
I'm uncomfortable working with the gas lines, so it may be time to call the technician for one more crack at it.
Thanks for your suggestions, I still have a lot to learn about this heater...

 

[ps0303]

I would have the tech come back out and look at it again. I wonder if any of the orifices are somewhat clogged thus creating the "whoosh" when it lights.

Do you hear it sparking and then it lights with the whoosh?

This is one of those issues where it's better to see it in person to determine what is actually happening.

 

[filmsmith]

Yes, you can hear it sparking before it lights with the whoosh. And when we tested the igniter it was definitely sparking. All the jets appeared to be clear, but I don't know if the manifold (or tubes) they are mounted in was carefully checked and cleaned. And as I mentioned, I'm not certain about the mounting and alignment of the pilot light either.

Either way way it goes, I want to have it rechecked before I buy a new heater, but I don't want to barbecue myself in the process, so I will definitely call a technician...

Thank you all for your suggestions. If you think of anything else please let me know.

 

[ps0303]

The mounting of the pilot can usually only be done one way so that really can't be messed up unless the burner tray is all rusted out and it was modified to make things fit.

 

[filmsmith]

Thanks Paul. That's good to know.

 

[Pool Clown]

I would maintain that there is something keeping the gas from getting to the pilot in a timely manner.

clogged jet(s) (right side of burner). Or improper positioning of the pilot? There is really just one way to mount it, unless it's bracket was rusted out and it got put back in kinda wonky.

Something obstructing between the pilot and the first rail. I don't know what, other than maybe a spider web.

I would check the jets. Now, just so we are all on the same page, the jets thread into the manifold. You will need a wrench or socket to get them off the manifold. They are maybe a half inch long. These aren't the burner rails that were replaced that are about 12" long. He will have to take the burner tray all the way out and all the burner rails off the burner tray as well, to get to the jets. It should take him at least a 1/2 hour to tear it down, and clean the jets.

 

[proavia]

To the OP:
There is a difference between the burner tubes and the burner orifices. Have a look at this diagram - specifically items 3 and 4:
Raypak Rheem Ruud 206A, 266A, 336A, 406A Digital Atmospheric Gas Heater Parts
In the link above, it appears each burner tube has its own orifice. The orifice is located at the end of the burner tube where the gas enters each burner tube. If gas isn't flowing through the orifice into the burner tube - especially nearest the pilot/igniter, gas may pool in other unobstructed orifice/tube areas causing the flame "woosh" you are experiencing once a bit of that pooling gas get back toward the ignition source.

The 2 gentlemen who have been assisting you are to 2 go to guys here for heater issues. They seem to be wanting you to check the burner orifices for blockage.

 

[filmsmith]

Thank you all for the information. I did not see the burner orifices and they were not mentioned in any of the repair discussions, so I believe it is possible that they were not checked or properly cleaned. I will have it done as soon as possible and will be there to confirm their condition.

Thanks again for your focus on this problem. TFP is definitely a valuable resource.

 

[filmsmith]

I want to thank everyone for the excellent feedback and suggestions with this problem. When I checked with the pool company they said their technician did not "notice" any problem with the orifices and that he did not see any blockage. As it turns out - he did not even check them.

A different technician showed up yesterday, and, as you suggested, we discovered that a number of the orifices were completely blocked and many were very restricted. The two orifices closest to the pilot light were among those that were completely blocked. We removed and cleaned them all and blew out the manifold and it started up immediately with no hesitation and no blowback.

It's aggravating that such an obvious issue was completely ignored and they tried to sell me a new heater rather than effect an obvious repair. It's like replacing a carburetor before checking a fuel pump, and then suggesting that the entire engine should be replaced.

But it's working fine now and you all deserve the credit for your great advice. TFP is a valuable resource and I will definitely support it! Thanks again for your very valuable help and keep up the good work.