Heater intermittently not coming on

doncaruana

LifeTime Supporter
Aug 25, 2011
325
Northville, Mi
A couple of years ago I replaced my thermistor and no problems since. That was the only issue I've had with the heater as we're winding down on it's eighth summer of usage. In the last week there've been a couple of times that it wouldn't come on. Each time, I shut off the pump, turned the temp down, turned the pump back on, then turned the temp back up and it kicked on and all was good.

So, obviously something is not quite right. And possibly even on it's way out. But I'm not sure exactly what and where to look. Any suggestions?
 

doncaruana

LifeTime Supporter
Aug 25, 2011
325
Northville, Mi
While I appreciate the link to the manual I've already read, the problem is that a) the issue is very sporadic and b) I was hoping for a little "tribe wisdom" before I have to start gutting the thing. Getting to the back of the control board is a pain.

I'd still appreciate any feedback from anybody. I'm the one who diagnosed and replaced the thermistor myself so it's not like I don't know my way around. But hopefully someone has some thoughts here before I have to take the heater apart.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,561
Northern NJ
The tribal wisdom is to look at the LEDs.

What do you find when you go out to the heater when it does not fire. Is the red “SERVICE SYSTEM”LED “on”? Is red “SERVICE HEATER”LED “on”?
 

setsailsoon

LifeTime Supporter
TFP Guide
Oct 25, 2015
1,572
Stuart/FL
Weird that there are no error messages or codes. I've had intermittent connection problems but always got an error message. The thermistor problem is the only one that wouldn't get an error message since the unit doesn't have any idea that it has failed. I've had a lot of these devices that I've played with over the years. If it's a 10K thermistor, the failure mechanism is they start to drift higher, then level off then drift again and pretty soon the are reading a resistance that translates to a temp that is above your set point so the unit turn the heat off. When you turn off the unit and re-power it will sometimes start low then quickly rise. So, I'd say you should replace it again. If you want to test this put an 8000 ohm across the thermistor connection. This should be read as about 90 deg F. If you have other than a 10 K thermistor look it up and get the resistance/temp chart for your controller and use the appropriate resister. This is only a temp test method, since your heater won't stop heating 'till it reaches the max heat setting and you lose the double protection. But it can save you waiting for delivery and the cost of the replacement.

Pool thermistors seem to vary widely in durability. My theory on this is that it has to do mostly with the housing. Many are cheap plastic that are subject to minute cracks from chlorine exposure. Some brands seem to use better plastics. The actual electronic part within the housing is the same and has a very high mtbf rate. When water intrudes it decreases the resistance which raises the temp reading. Pretty soon it fries and has almost no resistance or becomes an open circuit.

I hope this helps.

Chris