Jandy LT400 LP Gas Heater - rebuilt and fully functioning!

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J

Jameso78

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Sep 18, 2020
57
North Texas
Pool Size
45000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I thought I would take a few minutes and chronicle my recent experience in taking my Jandy LT400 heater from a pile of metal to fully functioning heater :) It is 14+ years old, and had been unused and non-functioning for 7+ years due to some underground (below concrete deck) plumbing issues for the spa... I was able to get those problems all repaired this summer, and so went to get my heater back operating. Here is a list of everything I had to repair/replace in the order of diagnosis:
  • Control Board - sent to BPengineering.com to be repaired since they are no longer available
  • Draft Inducer blower motor assembly - found used one on Ebay, also no longer available new
  • Hot Surface Igniter - used a Truestart universal igniter from Diversitech
  • Gas Valve - got a Honeywell universal valve on amazon - VR8345M4302 - the original part number on my LT400 was VR8305M4157
  • Flame Sensor - found a new one on Amazon
This was a fix one component at a time, then on to the next kind of process...all together I spent about $450 in parts...I used a multimeter and the Jandy LX/LT Troubleshooting flow chart, it certainly helped get through all the problems with the heater. It is now fully functioning again, used my spa last night and it was great! Happy to share any more details if anyone has an LT400 I can assist with...

cheers!!!
 
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Some advice on the inducer motors. Most all manufacturers that use these use a standard supplied component from companies such as Nutone. When the inducer went bad on my hayward it was still available from them, but, it was $450. I work part time in the HVAC industry so I was able to recognize that the inducer was the same unit that is in a lot of 80%+ furnaces. I was able to source the same unit from my local HVAC house for $129. Some judicious searching you can probably find a new replacement in the future from companies such as Supply house.com and others
 
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Thanks for the Info danpik... I was able to find a used one on Ebay for $85, it was the complete assembly including the housing... when I searched the Fasco model number there, a lot of used ones came up... I went ahead and replaced the capacitor with a new one to be safe, and it works like a champ! I have used Supply House as well, especially for PVC fittings you can't find at Lowes or Home Depot...I've had to repair some of my plumbing I referred to earlier, and their fittings saved me a bunch of headaches!
 
Well, I guess I claimed victory too soon... Last night went out to use the spa, and it went into the loop where it tries to start up all the way thru ignition, then the flames go out, induction motor spins up to high speed, re-lights again, etc it does this loop 3 times, then I get the Air Flow error code... I power it off and on, same sequence occurs again...its worked great for almost 2 weeks... I haven't used my multimeter yet for troubleshooting, but the flame sensor is new, the induction motor is working fine, and the hose to the air flow switch is clear... is it the air flow switch possibly, it has not been replaced? any other places I should look?
 
I have one other theory after reading a couple other threads... the difference last night (and continued today) is that we have had rain the past couple of days... when my flame ignites and stays lit for 12-15 seconds, it produces an excessive very high volume of steam, which I'm wondering plays havoc with the air flow switch, and causing it to shut down? I have double checked my new flame sensor rod and connection, it all looks fine...does the heat exchanger have drain holes to allow for moisture (rain) to evacuate? if so, could they be stopped up, allowing water to accumulate and thereby causing all the steam? I have been thru probably 8-10 repeat cycles of igniting 3 times, shutting off with the air flow error, and restarting, thinking maybe it would burn off the excess water, but it hasnt slowed down the steam production... I have not been into that part of the heater (yet)... just looking for some advice if anyone has seen this before....
 
The steam should not have an effect on the switch. The same switches are used in condensing furnaces all the time with no problems. Excessive water buildup can cause the problems you are experiencing though if the exchanger is designed such that the vacuum pulled thru it can be interfered with by an accumulation of water. Not being too familiar with this unit I can not recall how these exchangers are designed. I suspect they are like most 80% units and are an open design. Does the vacuum hose come from the blower and go directly to the switch?

I am somewhat hesitant to condemn the vacuum switch as it seems to be setting properly which is allowing the gas valve to open. As a test, you could try to jumper across the terminals on the switch to see if it stays running. This is a quick way to test these. Another method is to put a "T": in the vacuum line and hook up a vacuum gage and monitor the pressure to see if something happens at the shutdown point. If it stays running with the test jumper in place then that at least points us in the right direction. Sometimes, motors that sound like they are running good are nor performing at their best and do not pull enough suction to set the switches. I have seen this several times over the years in house furnaces.

Edit: The steam is most likely coming from the flue gas being too cold. Once the flue gas temp drops below ~150 degrees it allows the moisture to condense out causing steam.

Dan
 
thanks Danpik... yes, the vacuum hose comes directly from the blower assembly...I haven't done any additional troubleshooting yet, been to cold to spend any lengthy time outside! I'll try the jumper approach, that's easy enough, and might save me digging further into the heater unnecessarily...I went ahead and ordered a new switch just in case... its 14 yrs old, it will go bad eventually if its not already... maybe I'll bundle up later today and try the jumper to see if it makes any difference and report back, that won't take too long...thx!
 
ok...so I jumped the wires on the airflow switch, the results are basically the same, except it continuously repeats the lighting, stay lit for 15 seconds, stopping and restarting process, instead of stopping after 3 cycles and getting the airflow error light...what does that mean? assuming its not the airflow switch, where else should I be looking? Gas pressure maybe? Could the change in temperature be causing it to be a little too low? I have a regulator just outside my heater, I could try increasing its pressure potentially... I adjusted the new gas valve to spec for LP per the install instructions that came with it...
 

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OK... so I raised the gas pressure, both externally at the regulator and inside on the valve, no difference, so I set them back to where they were... I removed the top (lid) of the heat exchanger box, lots of rust on the baffles, but no standing water or anything... I cleaned all that out, put it back together, and still have the same issue... I am stumped at the moment... it worked great for 2 weeks, only change was the weather (cold and rain)... any other clues anyone?...
 
I got out the multimeter last night and did some checking... 24VAC on the purple wire attached to the air flow switch, and on the black/yellow wire as well when the induction blower spins up to high, as well as when blower slows for the igniter to kick on, all the way thru the gas valve opening and ignition... 2-3 seconds after ignition, the voltage drops to zero on the black/yellow wire, purple remains at 24VAC, and the gas valve shuts off within 12-15 seconds after ignition... this whole process repeats twice, then the airflow error occurs...based on reading other posts, it really sounds like the flame sense rod is bad, but its brand new (2-3 weeks since I installed it)... I went ahead and ordered another one just in case that's it...also thought maybe something has fallen over the top of the burner under the flame sense rod, preventing it from doing its job...I should have my new rod tomorrow, I'll try it first...if its still not working, I'll pull out the burner tray and see if there's anything there...any other suggestions ?
 
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ok... I am stumped... went out this evening, to do some more diagnostics, and heater worked normal... sooooo, I now have some theories to work thru... either it was temperature related, or moisture related... today was warmer and dry,,, will check back later this weekend...
 
Update... heater is still working fine, no issues the past 3 days after the rain stopped and outside temps warmed up... I did go ahead and replace my air flow switch since it is so old, thinking maybe there was a weakness there dealing with the temp/humidity changes...I also did check my gas pressures at the regulator and outlet side of gas valve, both were fine (12.5 WC on outlet side of regulator, spec is 10.5 - 14... 9.0 WC on outlet side of gas valve, spec is 9.0)... so next time it rains I'll check again to see what happens...
 
Grounding issues are notorious for causing the issue. Check the connection from the rod to ground and you should never need to replace it. Clean with a dollar bill nothing more abrasive as it will cause more problems down the road.

Congrats on your perseverance! 14 years is very good and a tribute to your water balance efforts.

This is a great thread, thanks for taking the time.

Chris
 
ajw22 said:
You may have a poor ground that gets bad when cold or damp in the flame rectification circuit. Read...

Heater Flame Sensing - Further Reading

www.troublefreepool.com www.troublefreepool.com
Click to expand...
Thanks for the info! I have thoroughly cleaned surfaces that I've worked thru so far (induction motor housing where it connects to the heat exchanger box, the connection of the flame sensor rod on the exchanger box, etc) I will look for some of these other spots noted in the article and see if there's some compromise in other grounding places...this article really does sound very similar to the challenges I was having...thanks again!!!
 
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Update... I have implemented the grounding fix suggested in the Fenwal doc referenced here - Heater Flame sensing errors caused by bad grounding issues
On my LT400, I ran a ground wire between the flange of my flame sensor and my new Honeywell Universal gas valve - it actually has a ground plug built on it, my old gas valve did not...also replaced all the baffles on my heat exchanger, half of them had rusted completely away (disintegrated - rust dust)... its all back together and working properly, the real test will be after it rains again...meanwhile, I'll just enjoy my spa and a nice glass of bourbon...stay tuned for the update after a rain shower has passed... Cheers!!!🥃🥃🥃🇺🇸🇺🇸🇺🇸
 
James,

Thanks for the follow up, it's always helpful to us and other members. I have the ground wire addition in mine from the blower flange directly into the ground gang in the electrical tray. Make sure you use wire rated for the high temps. Pentair actually sells a kit for the modification that includes the right wire to address the grounding wire issue. Another thing I did that maybe helping is to use Corrosion Block on all connections.

Good luck and fingers crossed!

Chris
 
Chris,

Thanks for the encouragement... these DIY forums like this one are invaluable to me, I've always done my own work whenever/wherever I can...we have a chance of rain next week, so we'll see how it goes! All my work and parts I've replaced is much much cheaper than a new heater for sure!!! As you said, fingers crossed! :lovetfp:🤞🤞🤞
 

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