Gas Heater Noise

[Woody007]

My Ray-Pak 400k makes an expansion noise, kind of a single light bang, every few minutes when running. I understand why it would do it if the flame were cycling on/off, but the flame is on all the time.
Just strikes me as odd the way it makes a noise like that when the water flow and flame are consistent. Probably does it every minute or so. Similar to sound if you were to tap on the outside cover for the heater, not a tic, tic tic type expansion noise.
Been doing it the last couple of seasons. Any ideas other than the obvious expansion of the manifold?

Edit to update:
After using shop vac to remove some leaves and then reversing the vac to blow around inside the heater it is no longer making the noise.
Not sure exactly what I did to fix it, but cleaning did the trick.
Thanks for your help!

 

[ajw22]

Let's see what @swamprat69 thinks.

 

[swamprat69]

Would be helpful to have exact Raypak model number and age of heater to be able to access the manual for the heater. Noise issues like yours are somewhat difficult to diagnose from offsite, but can be attempted with enough information. You should include all specific equipment information in your signature.

 

[Woody007]

Would be helpful to have exact Raypak model number and age of heater to be able to access the manual for the heater. Noise issues like yours are somewhat difficult to diagnose from offsite, but can be attempted with enough information. You should include all specific equipment information in your signature.

I don't see a tag on the outside of the heater but the manual is for models 206a, 266a, 336a and 406a. Rheem. Age is 4-5 years.

 

[ajw22]

Look on the inside of the door panel for the model number.

 

[Woody007]

Look on the inside of the door panel for the model number.

M 266A is what I found. Looked pretty clean in that area, vacuumed out a few leaves along the way.

 

[1poolman1]

M 266A is what I found. Looked pretty clean in that area, vacuumed out a few leaves along the way.

With the door off and he heater running from a couple of feet away, get down and look at the burners. Its better/safer if you can use a hand- mirror if possible. Is there flame on all of them? A clogged orifice or debris on a burner can cause that issue.

 

[Woody007]

With the door off and he heater running from a couple of feet away, get down and look at the burners. Its better/safer if you can use a hand- mirror if possible. Is there flame on all of them? A clogged orifice or debris on a burner can cause that issue.

I'll check that out. I can hear them, but one could certainly be out and couldn't tell the difference from outside.
Any cleaning tips if I see one of the burners not working? I haven't really done any work on pool heater, so not too familiar with it.

 

[Woody007]

With the door off and he heater running from a couple of feet away, get down and look at the burners. Its better/safer if you can use a hand- mirror if possible. Is there flame on all of them? A clogged orifice or debris on a burner can cause that issue.

Best I can tell the flames look good. It's more of a "field" of blue flames vs a jet going down a tube like a furnace. Can't clearly see all of it, but what I could see looked ok.
I only let it run a few minutes, but didn't hear the sound so I couldn't isolate where it may be from.

 

[1poolman1]

Field of blue, yes. You have an atmospheric heater. Vacuuming may have removed the cause of the problem. You don't have a 400K if the rating plate says M266. Its a 266K BTU model.

 

[Woody007]

Field of blue, yes. You have an atmospheric heater. Vacuuming may have removed the cause of the problem. You don't have a 400K if the rating plate says M266. Its a 266K BTU model.

What do you think is actually causing the noise? It seems to be more of a mechanical noise than the sound of a flame out but can't say for certain.
Regarding the size, I just went on what the installers told me, but they were wrong about more than one thing. It does a good job though.