Laars LT low nox pool heater - seviceman 'stumped'

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Poolhaven

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May 19, 2014
12
New Jersey
Hello all,

I have a Laars LT low nox pool heater (>2003 model) - heater won't work.

Between myself and one pool serviceman troubleshooted the heater but still can't figure out what is wrong. Perhaps someone can help!? Here is the issue:

We followed the following appropriate manual (see link) on page 16 and 17 --- http://www.victormfg.com/_build/docs/prodguides/JandyPoolHeaterTroubleshootingGuides.pdf

(this is the laars LT low nox pool heater troubleshooting manual)

steps 1, 2, and 3 are fine
step 4 - fan is on, yes.
says skip to step 5.
step 5, yes, working (24 vac purple wire at both ignition and ignition control terminal are fine)

step 6:
hot surface ignitor glowing? No.
turned power off - ohm test 60 ohms - confirms working
which suggests ignition control is faulty.

I purchased $200 exact model and replaced. However, still NO change.

I turn on for heat - and fan turns on, I hear click, gas turns on... but again, burners do not turn on and it recycles these steps x 3 and then turns off.

So... I then (just in case) replaced the HSI (hot surface ignitor) with brand new one.

Again, NO change in above pattern.

I nor the pool serviceman was able to find a 'short' anywhere.

Any suggestions please??

Thank you!!!!!! :(
 
It's possible that the old ignitor shorted out the new control module before you replaced the ignitor. What is the part number of the module you used to replace it with?
 
I work on a lot of hot water makers ( large commercial water heaters for apartment buildings) Laars is on of the brands that deal with. You possible could have too much air. Ive had units where it blows enough air down the burner tubes and will not let the burners light. You might need to throttle back on the air. There should be an adjustable air damper on the blower.
 
There is no damper on the blower. Blowers on pool heaters suck air out, an exhaust. Plus he says the ignitor is NOT glowing.

Poolhaven, have you tested to see if the module is in fact putting voltage to the ignitor?
 
My apologies --- I actually replaced the ignitor before installing the new control module as I thought that was the initial problem. Any difference in suggestion given that info? Thanks.

- - - Updated - - -

Poolhaven, have you tested to see if the module is in fact putting voltage to the ignitor?

Not yet :) will try that it in am (dark here). Thanks for the suggestion.
 
Finally got chance to reassess.

So to update anyone that can lend a helpful suggestion - I have a laars lt low nox pool heater
The ags light went on early spring

Ultimately I repalced the ignition control , the hot surface ignitor and the hsi still did not light
Finally found a burn on the control module and repalced it.

Thankfully, now the hot surface ignotor lghts up and the burners then turn on but within few seconds the burners turn back off and the fan turns on

It does this only one cycle and then the ags light goes on again

Based on this algorithm - http://www.fwwebb.com/docs/JandyPoolHeaterTroubleshootingGuides.pdf
Page 16-17 is the heater version I have

It seems its now stating I should replace the thermostat.

But 1) anyone agree? If not - any other suggestion?
2) where is the thermostat?

Thank you!!!

Ps - I had a second serviceman confirm that the control module was not functioning - so was glad that after buying this part $125 (plus the hsi and ignition control purchases) the hsi now at least is working. But now I'm out >$500 total. Ugh. Can't imagine asking another serviceman to come back and tell me what else needs to be fixed as I keep paying more $ for someone to tell me buy another part.

Please help! Thanks again.
2)
 
AGS - Automatic Gas Shutdown simply means the Ignition Control did not sense flame rectification. Make certain all gas cocks are open, and there is sufficient gas pressure and volume (gas line sized properly). If the heater fires and then the flame goes out quickly, it indicates the rectification signal is not returning to the Ignition Control. Check for poor or missing ground wire..

Could it truly be faulty ground wire? Instead of the thermostat. As this is exactly what's hsppening... Heater fires and then flame goes out quickly.
 
hoosierrun said:
Definitely.
The ground is as important as a power wire. You need both. I hope that fixes it.
Click to expand...

There seems to be a few ground wires within the system. Two of them are within the circuits inside the heater unit and another one is 'outside' of the unit (along the base of the heater side door and then grounds to another ground wire at the pool pump. Which wire would I need to change?

Thanks

- - - Updated - - -

See below

Poolhaven said:
AGS - Automatic Gas Shutdown simply means the Ignition Control did not sense flame rectification. Make certain all gas cocks are open, and there is sufficient gas pressure and volume (gas line sized properly). If the heater fires and then the flame goes out quickly, it indicates the rectification signal is not returning to the Ignition Control. Check for poor or missing ground wire..

Response:
All gas cocks are open and gas pressure/volume are appropriate.

Can u suggest 'how to check' which ground wire might not be working?

Thanks

Could it truly be faulty ground wire? Instead of the thermostat. As this is exactly what's hsppening... Heater fires and then flame goes out quickly.
Click to expand...
 

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As for the grounds, I'd slightly loosen any screws and twist the back an forth a little to clean the contact surfaces and then retighten them. If they're spade plugs, unplug and replug them a few times to clean the contact surfaces.
 
There is also the possibility that the heat exchanger could be sooted up causing the flames to roll around inside. Can you see the flames? Maybe a lazy flame. I also believe your unit has a separate flame sensor. Have you tested it?
 
Poolhaven said:
No spider webs seen

Thanks!
Click to expand...

It's very hard to see spider webs in the orifices. It's best to take a pipe cleaner and push it into each one just in case they are there. You can also run a bottle brush, that's what I use carefully, thru the burners. In order to do this you have to remove the gas manifold.
 
The webs are on the inside of the gas nozzle so you have to remove them to see them. Did you remove them?
 
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