Laars pool heater cuts off

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  #1  
Old 10-05-10, 10:15 AM
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Laars pool heater cuts off

I have a Laars Series 2 ESC pool heater. When I turn it on, the ignitor works and the pilot comes on, followed by the main burner. Then, in just a few seconds, the gas is cut off. The ignitor starts again and the cycle repeats. The Honeywell S8600F controller is getting a solid 24VAC, I have checked all the various sensors (replaced the fusible link...). When I apply 24VAC directly to the main gas valve, the heater will stay on. I have cleaned everything up as best I can. I am thinking it must be either the Honeywell controller, or the pilot ignitor/sensor. I even clipped on a temporary ground wire directly to the sensor bracket to try to eliminate grounding problems. I think the ignitor/sensor was replaced a few years ago, it looks fine.
This heater is 15 years old, not leaking but pretty rusty, not worth spending a lot of money on. I am trying to avoid buying a replacement Honeywell controller (or a new heater!). Is there some way to test the pilot ignitor/sensor?
 
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  #2  
Old 10-05-10, 01:55 PM
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There will be a few devices that are wired in series that will shut off that gas valve. A gas psi switch, an over temperature switch (snap disc), your thermostat, and possibly a bad solenoid coil...and maybe other safety devices/sensors.

If you put a volt meter across the 2 wires that enter the valve, and you know for sure that these are the 2 for the main valve, and you read:

24vac, uninterrupted, and the burner shuts...you may have a bad coil on that solenoid. To further check that, hook up an amp meter (you need to do this 100%correctly), and set the meter for mA. When the valve turns on, you should read a constant amperage as current flows through the coil. If that current stops at the same time your valve shuts off, and you still have 24vac on those 2 wires, then your coil is open (junk).

If your meter read 24vac and as the gas valve shuts off the meter goes to 0V, then one of your sensors are opening that circuit. You can use a jumper to troubleshoot which sensor is opening up. Just clip a wire across each sensors terminal until it works.
 
  #3  
Old 10-05-10, 02:26 PM
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Thanks for the reply. I have tested all the devices that might cut off the gas and they are all working fine (I had to replace the fusable link). The solenoids are working fine because I can apply 24vac directly to them and the gas flows. I even tested the rectifier diodes and the two filter capacitors that convert the 24vac to dc for the solenoids. What is cutting off the 24vac is the Honeywell controller. As far as I can tell, given that the 24vac is good, the only reason the Honeywell controller would turn off the gas after it turns on the main burner is because it thinks the pilot light is off. Since the pilot light is not off, it must be the pilot ignitor/sensor or the Honeywell controller itself at fault. I am trying to determine which one is the problem, without buying a new Honeywell controller. So I am looking for a way to independently test the ignitor/sensor.
 
  #4  
Old 10-05-10, 02:34 PM
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Also, there must be a flame sensor for your main burner. This might be a thermocouple or some other switch that detects that your pouring a load of fuel throught the burners and that it is being ignited.

On newer furnaces/water heaters there is a PLC or some sort of controller that takes these inputs and, thus, outputs accordingly. The problem is that you need to be able to read the program in order to know why the logic is working the way it is (working or not working correctly). Unfortunately, we will never get these programs from the manufaturer and therefore you get to call a service person to plug in and read why the heater isn't working.

If you understand the basic principles of the unit, you can sometimes figure out what's wrong. However, if the PLC/controller is bad (faulty input/output), then you're looking at a lot of guess work before calling for service.

Also, if you have a carbon-type ignitor, it might work initially, but as it heats up it can expand and open that circuit...which could be another fail-safe in an ignition circuit. I have seen these carbon heating elements crack and you would need a magnifying glass to see it. You will read 1 ohm with a meter, but if you grab it and separate it a tad, you will see the crack. Just an afterthought.

Good luck. Don't let this thing beat you!!
 
  #5  
Old 10-05-10, 03:43 PM
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Sounds like you're right there.

I think I would go out and buy a cheap t/c and plug it into your Honeywell and put a torch on it to see if the valve stays open. Or wing it and buy the replacement t/c and replace it.
 
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