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Old 03-14-2015, 05:09 PM   #1
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Jacuzzi heater gone crazy


Never mind the hissing sound, my wife was blowing out the lawnmower. It's the clanking sound that really has me concerned. It's pretty violent, enough that the whole unit is moving around. It sure sounds to be coming from inside the heat exchanger area but I can't find anything moving around.

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Old 03-14-2015, 06:59 PM   #2
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Sounds to me like it's trying to lite (clicking sound). Additionally, it looks like the flame is moving all around heat exchanger and coming out of the bottom at times. Could be a cracked/bad heat exchanger. Idk. Just guessing. I'd have it looked at by a pro. Just a suggestion.

Others will be along with more advice/suggestions.
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Old 03-15-2015, 02:30 AM   #3
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Talked to a pro. The burners light it's a pressure bypass in the manifold. It's like a car radiator thermostat and the spring is broken.
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Old 03-15-2015, 08:20 AM   #4
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A number of things can be causing that, The first is thermal shock. The fins are expanding rapidly because of the heat and the colder the fins are (the coder the water is) the worse the sound will be. If you watch at the beginning carefully you can see the flame yellow a bit at the exact same time a popping is heard. As a fin adjusts itself it displaces a wave if air which can be seen by the slightly yellowing flame.

The other possible cause is a scale or crud build up inside the tubes. Scale acts as an insulation and traps a tiny unit of water which super heats really fast, flashes to steam and then back to water as it is forced out from its insulated location back into the cooler surrounding water (a miniature explosion). That however would also rattle the fins and send an air wave to the flame so it's not really possible to tell which is going on from the video.

Do a chemical wash inside the tubes and make sure they're clean. Try to avoid a large flame and having it come in direct contact with the fins, and if your spa water is dead cold then lower the flame level and SLOWLY bring it up to temperature. I do large commercial boilers and it can take me days to warm up a large system due to thermal shock. The "mini explosions" aren't so mini in a large system and if not done slowly then you can literally watch as 18 inch steam lines jump an inch or two off their hangers.

After the water is uniformly warm then you can increase the heat level a bit... but if the water is dead cold you have to use a low flame.
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Old 03-16-2015, 10:47 AM   #5
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Hot tub gas heater with plugged heat exchanger


That looks like an old Teledyne Laars 50,000 BTU heater. The heat exchanger does not appear to be plugged.

I don't recall if that heater had a water mixing valve on the discharge of the heat exchanger.... If it has a valve, that might explain the noise but does not explain the gas valve cycling unless the exchanger is getting really hot and it doesn't seem to stay lit long enough for that to happen.

Check the pressure switch.

Ensure adequate, steady water flow. Ensure adequate water in the tub so you aren't sucking air through the plumbing. Remove the filter cartridge if it's dirty or plugged. Test the pressure switch with an Ohm meter.

The pressure switch should be closed when water is flowing. More importantly: It should be open when the water flow stops.

If the pressure switch is dropping out (open), the gas valve will shut down the burner. When the pressure switch kicks in again it will attempt to light again.

All the clicking sounds like the gas valve opening and closing because it's trying to follow the malfunctioning pressure switch.

Tom Davis, Owner
Affordable Hot Tub Repair
San Diego, CA

Last edited by Tomedav; 03-16-2015 at 11:06 AM. Reason: (Actually watched the video)
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Old 03-16-2015, 09:19 PM   #6
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Quote:
Originally Posted by Tomedav View Post
That looks like an old Teledyne Laars 50,000 BTU heater. The heat exchanger does not appear to be plugged.

I don't recall if that heater had a water mixing valve on the discharge of the heat exchanger.... If it has a valve, that might explain the noise but does not explain the gas valve cycling unless the exchanger is getting really hot and it doesn't seem to stay lit long enough for that to happen.

Check the pressure switch.

Ensure adequate, steady water flow. Ensure adequate water in the tub so you aren't sucking air through the plumbing. Remove the filter cartridge if it's dirty or plugged. Test the pressure switch with an Ohm meter.

The pressure switch should be closed when water is flowing. More importantly: It should be open when the water flow stops.

If the pressure switch is dropping out (open), the gas valve will shut down the burner. When the pressure switch kicks in again it will attempt to light again.

All the clicking sounds like the gas valve opening and closing because it's trying to follow the malfunctioning pressure switch.

Tom Davis, Owner
Affordable Hot Tub Repair
San Diego, CA

I probably shouldn't have done this but I bypassed all that in testing. Went straight from the transformer to the solenoid (pump running at the time) and it still did it.

The video doesn't really capture it but it sounds like a large bolt shaken around in a cast iron pot. the sound does not seem to be coming from the solenoid. The reason I zoomed in on the wire was to show how much the entire unit was shaking.

You are correct, it's a teledyne GTG-50 on a calspas setup. We are in the IE and have no pool. the kids (4 & 9) spend the whole summer in that thing.

Last edited by five.five-six; 03-16-2015 at 09:23 PM.
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Old 03-17-2015, 10:55 AM   #7
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Quote:
Originally Posted by five.five-six View Post
I probably shouldn't have done this but I bypassed all that in testing. Went straight from the transformer to the solenoid (pump running at the time) and it still did it.

The video doesn't really capture it but it sounds like a large bolt shaken around in a cast iron pot. the sound does not seem to be coming from the solenoid. The reason I zoomed in on the wire was to show how much the entire unit was shaking.

You are correct, it's a teledyne GTG-50 on a calspas setup. We are in the IE and have no pool. the kids (4 & 9) spend the whole summer in that thing.
All I can say to that: Hire somebody who can troubleshoot without bypassing all the control and safety devices.

Like somebody else on this thread suggested: you are probably boiling water. All the banging comes from the little steam explosions inside heat exchanger. With the pressure switch and high limits bypassed, you are just playing around with a potential steam-bomb.

I still can't confirm if the older Teledyne version of that heater had a bypass valve. I don't recall ever changing one when I worked for a Cal Spa dealership in the 90's and we sold a lot of those gas packs. We often plumbed a bypass using PVC pipe and a gate valve so we could control the temperature rise manually.

See parts diagram item #40, 41, 43 https://www.parts4heating.com/v/vspf...fs/Telstar.pdf

Either way, the heater is so old you might have trouble finding parts.

Tom Davis, Owner
Affordable Hot Tub Repair
San Diego, CA
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Old 03-17-2015, 11:52 AM   #8
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Quote:
Originally Posted by Tomedav View Post
I still can't confirm if the older Teledyne version of that heater had a bypass valve. I don't recall ever changing one when I worked for a Cal Spa dealership in the 90's and we sold a lot of those gas packs. We often plumbed a bypass using PVC pipe and a gate valve so we could control the temperature rise manually.
A few months back, months before this started happening, I took the whole thing apart because it was heating slowly. I suspected calcium buildup inside the heat exchanger so I flushed it with vinegar. That helped a little, but I did notice that there is a spring bypass thing in the manifold.


WE are considering replacing it. We are also strongly considering installing an in-ground pool in the next few years. My thinking is to either replace it with an inexpensive used heater or spend the bucks to buy a heater that would serve the future in-ground pool we want to buy.
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