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Laars Lt400N Fenwal Module Problem


Bugman1400

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I typically pride myself in being a LAARS pool heater expert on this forum but, this problem has me stumped. My symptoms include:

1.) Exhaust fan comes on but, HSI does not.

2.) I never hear the gas valve click.

3.) HSI shows continuity w/ 70 ohms and does appear to have any breaks. I believe this is a 240VAC ignitor.

4.) The L1 & L2 wires into the FENWAL 05-332161-103 have 240VAC between them and 120VAC to ground for both.

5.) The IGN/240 and IGN terminals on the FENWAL show low/no voltage between them and low/no voltage to ground during the cycle period.

6.) The flame sensor wire seemed very questionable and is now broken (due to yours truly).

Questions:

1.) I know the flame sensor is critical after the flame is established but, does the FENWAL check for it first before it activates the HSI? If so, is there a way to fake the signal?

2.) God help anyone trying to find a 05-33 replacement. It seems the 05-33 is the old analog type and has been replaced by the 05-66. However, the FENWAL conversion guide dated Feb. 11,2003 indicates that the replacement for my FENWAL 05-332161-103 is the 35-662534-113 which seems to be very ellusive to find. Does anyone know where I can find a decent replacement without the +$300 price tag that I've seen most places?

3.) Any additional tests that I can try other than to see how flat it gets after I run over it?

Many thanks!

UPDATE: I was able to reattach the wire to the flame sensor but, can't be sure if its truly fixed. I still get nothing from the HSI. Is there any other ways to bench test the FENWAL module?

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  • 3 weeks later...

I think the problem is with the blower, or the air switch. Although it is coming on, the blower may not be moving enough air to satisfy the air switch. This happens sometimes to the blower motor if it looses one winding. Or something is keeping the air switch from closing. Not enough air, spider in air tube, chewed tube, etc.

Here is the sequence more or less (Not all heaters fire in the same way, but this is close to what they all do)

1. call for heat

2. Safety circuit closes, or has been closed ever since the pump had started, and is just waiting for a heat call.

3. fenwall closes blower switch, blower spools up.

4. Fenwall then waiting for a signal from either control board or from air switch directly that it has closed THEN sends igniter voltage and begins the ignition process (glows or jumps gap).

5. After igniter has had voltage for a predetermined amount of time, gas valve opens (click)

6. Burners ignite (hopefully).

7. At this point, if flame rectification does not occur within a few seconds, gas valve will close.

Then the whole circus starts again two more times before it hard locks out.

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  • 4 months later...

I have read through your many previous posts on lighting issues on the 400 LX and LT, and I have a tale to tell...

We purchased a foreclosed home that a flipper tried to sell, but was foreclosed on as well. The heater was not used in years, and even had a mudflow cover the bottom 1-2" of the unit. Before that happened, the power distribution board popped out of its plastic housing and shorted out. I have replaced this. The gas line was not connected, so a plumber came in and connected it, and verified gas pressure.

After the gas was reconnected, it would not light, so I removed and cleaned all the orifices. Then the unit fired, and it started banging. I replaced the bypass (spring and end were missing). Now, it gets past #7 above, but when the fan goes high, the gas shuts off, and I get an airflow message. The blower switch is holding 24 VAC at the switch on both sides during this sequence, so I suspect some other event is causing the gas to shut down. Is it strange it went from working to not working after this event? Did it overheat or damage itself?

To be clear, blower circuit is closed at step #4, opens during some point after #6, and instantly closes again when high blower is commanded. The high blower stays on after the gas shuts off, high blower cycles off, and the sequence happens again. After the second time, Service/Air Flow lights are on the panel, no lights on Fenwal. Since I started checking things (wire brush to burner tube, checked/secured blower tube, checked flame rod, reassembled unit), it now only goes on high for a second where I was getting up to 10 before. I do notice the troubleshooting says to swap out the GUI, but that is an expensive fix.

Some previous threads mention that the burner might need to be cleaned, or the flame rod should be cleaned (looks almost new to me, except for the rust on the mounting bracket, but I have never seen one before this). I read that problems with either of these parts might show up when the blower goes to high. I tried removing the top of the burner housing (the part the blower attaches to, but It appears sealed with silicone or something. As for bottom access, is it a good idea to run shop air in the burner tube to remove any blockage, or do you have to take the burner cover off the bottom side to properly clean? This appears to be attached to the gas distribution bar, so I thought it might be more trouble than its worth. As for the flame rod, one guy said to bend it 45 degrees to keep flame contact. Also, the flame rod appears to be a single wire, so are you supposed to test it for resistance?

Also, the sooting issue. I have never seen this on a pool heater (last home had Laars millivolt from the 80's, looked clean, this is a low Nox from 2001, if that matters). When the fan goes high, air is really moving and when it did work previously, the air was not too hot to put your hand in front of the blower.

Finally, since the gas pressure is good, could the gas valve be damaged? It was exposed to the elements, and I tried vacuuming cobwebs and pine needles out of it. I am also curious if more gas comes out when the blower goes to high. If not, sounds like the gas valve is ok.

Thanks in advance

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Fixed. The metal on the burner directly below the flame sensor was oxidized, which made a poor path to ground. I sanded it down, and everything works.

I did experience the Zodiac tech support indifference, These units are pretty straightforward, but because of incorrect error messages, limited troubleshooting guides, and a mixture of water, gas and electricity, finding someone who has the knowledge and patience to figure these things out will be difficult. That being said, I cannot imagine that even the latest models wouldn't suffer from the same problem, unless they moved to UV flame detection or some other technology.

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