Hayward H400IDL pool heater rust on burn tubes, corrosion on heat exchanger


New member
Sep 5, 2009
I just took apart my 16 year old Hayward natural gas pool heater to inspect the burners and heat exchanger. I'm wondering if someone more knowledge than I am could look at the attached pictures and advise me if they thought it was time to purchase a new heater?

I showed the pics to my local Leslie's Pool manager (someone I've known for years and trust) and he thought the heat exchanger corrosion was bad enough to require a replacement heater. He didn't advise just replacing the heat exchanger as it's an expensive item for an old heater.

Just looking for a second opinion and more advice.

Thank you,


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Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Welcome to TFP.

Lets let @swamprat69 declare it terminal. I would Not put more money into it.


Well-known member
Mar 30, 2019
Las Vegas, NV
Was there a specific reason that you took the heater apart to inspect the burners and heat exchanger e.g. (fault code, leaking heat exchanger or generally not operating normally)? What you are calling heat exchanger corrosion only appears near the header ends of the heat exchanger (can't really see the whole heat exchanger). What I am seeing is some sooting (carbon) at the edges of the heat exchanger which is an indication of incomplete combustion. Also the rusting patterns on the burners indicate the possibility of incomplete combustion and and a situation very close to (if not) flame rollout. I can only see the top side of the heat exchanger. You should inspect the underside of the heat exchanger for sooting (blockage). I have been nursing a ~15 yr. old Hayward H400IDL2BH for the past 9 yrs. , but I don't think out heater models/configurations are the same ( different hot surface ignitors and if that is your complete model number you seem to have a 2 speed inducer motor whereas mine is single speed). Also an H400IDL does not seem to use a fenwal ignition module, but controls ignition from the main control module (which fires on low inducer speed and moves to high inducer speed after flame is proven). Any more information you can give would be helpful as would overall photos of heater and controls with covers off and verification of complete model and serial number. This is the manual that I am looking at https://images.inyopools.com/cloud/documents/hayward-heaters-h-series-low-nox.pdf Correct me if I am wrong.


New member
Sep 5, 2009
Hello and thank you for this information and the web link to the Hayward H400IDL manual. I hadn't located that specific manual on my web search.

My heater is a Hayward H400IDL Serial Number 3104. Pic of label attached.

I've reassembled the heater and now wish I would have taken more pictures while disassembled but attached are a few more pics from when it was being disassembled yesterday.

I had detected an intermittent problem with the heater for the last couple of weeks in that twice I heard the flame stop while heating the pool water, then a few seconds later the flame would start up again. This was when I had set the heater to heat to 85 degree and the pool water was around 70 or so. Then, the other day the heater sort of rattled or seem to jump for a second with a banging sound, not loud but I heard it as I was near the heater. It was that event that prompted me to want to take a look at the heat exchanger and manifold parts.

I'm curious as to why the heat exchanger shows what I assume to be corrosion at both ends of the unit, but none in the middle. The manager at Leslie's thought it might have something to do with my Aquarite cell not having a one way valve between it and the pipe to the heater.

I enjoy working on equipment and this is turning out to be a good education on pool heaters. Likely, I will have to spend around $4K to buy a new Hayward heater but before I make that decision I'd like to confirm mine is not a candidate for repair.



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TFP Expert
Mar 2, 2011
The heat exchanger probably has a slow leak.

The copper looks like the pH has been too low at some recent point.

Your plaster looks like it has some copper staining.


Well-known member
Mar 30, 2019
Las Vegas, NV
Banging/rattling is usually an indication of a water flow problem. Is the filter clean and were the bypass valve/flow control thermostat not corroded or showing a buildup when you removed the water header? I am still very concerned about the visible soot on the top of the heat exchanger. You really need to inspect the underside of the heat exchanger for sooting (flashlight and mirror) to make sure it is not partially or fully blocked. The flame sensor looks like it should be cleaned (steel wool or small metal/diamond file). Burner slots should be cleaned with a wire brush. Inside of burner tubes and gas manifold orifices should be inspected/cleaned to make sure that they are free of spider webs.


Well-known member
Mar 30, 2019
Las Vegas, NV
As to the heat exchanger being clear in the middle of the top...if the underside is blocked by soot, the easiest path for combustion byproducts may be near the ends of the heat exchanger due to slightly larger openings?
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