Max-E-Therm Won't Stay On

[JWeiss]

Just opened up for the season this week, and diagnosing a heater problem. It's a Max-E-Therm 400 NG heater, about 7 years old. New igniter was installed last year. Controlled by IntelliCenter ("IC") via Fireman's Switch, and running on 120v. Heater panel is set to max temp (104F). IC is set for 70F; current water temp is 55F (agreed by both IC sensor and heater).

When I turn heat on at IC, the heater goes through normal startup, and ignites as normal. LED8 ("heating") stays on. After anywhere from 2-5 minutes, the flame cuts off, LED8 goes into "heat demand" mode (flashing continuously). About 30 seconds later, it reignites, LED8 goes solid, but will only run for less than a minute. The cycles continue this way for at least four cycles (as long as I've let it go thus far). Behavior is the same after I shut off heat, give it a rest and start over calling for heat (i.e., initial multi-minute run, followed by half-minute cycles).

There are no diagnostic lights at any point on the control board nor on the Fenwal ICM. The Service light never comes on, nor any of the specific sensor fault indicators. The ICM does not go into lockout, as it appears it is happy with each ignition. There is definitely air flow through the blower (I can feel the suction when I bring my hand to cover the intake). Tubes to the AFS seem to be clear. Heating canister seems to be intact (I can see no heavy corrosion areas at least in what's visible).

Any thoughts on the likely faults here? Is it likely that the igniter loses flame sense and shuts down (if so, would there be a diagnostic at the ICM or control board)? I haven't pulled the igniter yet for a visual, but as I mentioned above, it's quite new. I wonder if the shortened cycles after the initial one are due to the fact that the igniter is more fully heated from the first on cycle?

 

[ajw22]

Put a manometer on the gas valve and check the gas pressures as the heater cycles.

You may have a flame sense problem - Heater Flame Sensing - Further Reading

You may want to install MASTERTEMP® & MAX-E-THERM® HEATER GROUND WIRE KIT (KIT P/N 475214Z) whose instructions are attached to this post.

 

[JWeiss]

Thanks for this. Unfortunately, I don't have a manometer, so can't check pressure. Your link for flame sense problems is not working, but I'll do a specific search on that. I am aware that ground flakiness can lead to flame sense problems. The ground kit seems straightforward enough - seems I ought to be able to accomplish this with stranded ground wire and lugs that I have in my inventory.

 

[ajw22]

Your link for flame sense problems is not working, but I'll do a specific search on that.

Heater Flame Sensing - Further Reading

www.troublefreepool.com

 

[JWeiss]

Today's diagnostics (focused on flame sensing)... Checked static resistance across several different ground points: bond wire, electrical ground wire, various points of frame, yellow grounded conductor in control box, flame holder nuts. All combinations measured down to meter resistance (virtual zero). Installed a ground wire as per the kit from under the flame holder to the ground screw for the yellow wire at the control box bottom.

Next, I read DC voltage (using a DMM) at the ICM FC+/- pins. Consistent with the flame cycling described above, upon first ignition (which held flame for 3-4 minutes), the voltage rose fairly quickly to above 4VDC and then slowly started to drop. When it got down to about 0.3VDC, the flame cut out. I cannot tell for sure if combustion stops and is then quickly followed by gas shutoff, or if gas shutoff is what causes combustion to stop. Subsequent cycles (each with about 1/2 minute breathing delay) stay lit only about 1/2 minute with the voltage rising to only about 0.6VDC and then slowly falling to the 0.3 - 0.4 range before flame cutoff.

Finally, I pulled the igniter (again, new since last season) and don't like what I see. No obvious cracks or damage to the igniter itself, but there was some white foamy stuff present. Also, worse still, the igniter port seems quite corroded, with a rusted layer coming off with the igniter. Pictures are below. Do we think the heater is a goner at this point?

 

[ajw22]

I think your heat exchanger is leaking.

The water is dripping on the ignitor which is your flame sensor and killing the flame sense.

You don't see the small leak with the water evaporating from the heat.

The rust seen in your pics is not a good sign.

 

[JWeiss]

I think your heat exchanger is leaking.

The water is dripping on the ignitor which is your flame sensor and killing the flame sense.

You don't see the small leak with the water evaporating from the heat.

The rust sen in your pics is not a good sign.

That was my fear as soon as I pulled the igniter. I suppose the leak starts to really manifest as the canister heats up, causing the subsequent cycles to be shorter than the first.

 

[drewgost]

That was my fear as soon as I pulled the igniter. I suppose the leak starts to really manifest as the canister heats up, causing the subsequent cycles to be shorter than the first.

Hey J anymore info on this problem as I am having the exact issue, no faults or lights just keeps cycling on and off forever! was it the igniter?
Thanks,
Drew

 

[drewgost]

Thank you, I bought a new igniter and the heater is up and running! Now to tackle the high pitch sound

 

[JWeiss]

Sorry to have missed your question. We guessed the igniter was likely fouling due to heat exchanger leakage, and decided to replace the entire unit. Not thrilled with 7-year lifespan, but we did it anyway. Went with the cupronickel option for hopefully better longevity. If you've replaced the igniter, you may want to pull it (carefully!) after a while and see what it looks like.

 

[drewgost]

Sorry to have missed your question. We guessed the igniter was likely fouling due to heat exchanger leakage, and decided to replace the entire unit. Not thrilled with 7-year lifespan, but we did it anyway. Went with the cupronickel option for hopefully better longevity. If you've replaced the igniter, you may want to pull it (carefully!) after a while and see what it looks like.

Thanks J