Pool heater turns off if there's too much return flow?

Jun 23, 2017
61
Sparta, NJ
Pool Size
30000
Surface
Plaster
Chlorine
Liquid Chlorine
I'm still figuring out how our pool works. We have an oil fired heater and I'm having the complete opposite issue to what I expected.

Last fall, after we bought the house, we turned on the heater to try and get at least one use of the pool before it was closed for the winter. I started it in the evening and left it and the pump running overnight. The heater shut off at some point during the night, leaving the pool at a brisk 64 degrees (one of my nieces still jumped in the pool, but us adults sat it out). When the pool guys opened the pool this spring I asked about it and he said that it was likely that my filter was clogged and there wasn't enough water flow through the heater so it cut off, which made sense.

However, we're still having problems with the heater turning off. I know my filter is relatively clean and the pressure is roughly at the same point it was when I last cleaned the filter 10 days ago (stuff stopped falling out of the trees and into the pool for a little while). However, the heater shuts off unless I turn the diverter valve on my returns to almost the off setting. I'm assuming this is causing the water to "back up" and move slower through the heater which is causing it to decide to stay on. Even when I get it to stay on, if I then unplug Polaris from his wall fitting the heater cuts off - again, I'm assuming it's because the return flow then has less restriction. Does this sound at all correct? Does anyone have any suggestions on how to run the heater with a reasonable amount of return flow, as this doesn't seem like it's the way things are supposed to work. Does this suggest that something's not right and needs cleaned/serviced/replaced?

One thing I will note is that our return pipes have no nozzles on them, so it's free flow out of 2" pipes into the pool. I've ordered a selection of nozzles to see which ones would work, which I assume would restrict the return flow a little but I'm not sure how much difference it'll make. Help me please, as I keep getting calls at work from my wife and kids when they're once again doing battle with the selection of valves trying to get them in just the right place to warm up the pool.
 
If you do not have enough back pressure, it could cause the heater to not fire. Adding the "nozzles" to the pool returns could create the back pressure you need.
 
Thanks for the advice. Looking at the manual it looks like there's a thumb wheel for the pressure switch to adjust the sensitivity, which I can try if my nozzles don't help enough. I liked how the manual described how to turn the thumb wheel without giving too good an indication of whereabouts you find it (all I could really see it on was the exploded diagram at the end) - perhaps I'll need to do that investigation while my wife is busy elsewhere so she doesn't see me deconstructing the heater in search of a tiny wheel.
 
Be careful with adjusting the pressure switch. I usually advise not to mess with the factory setting on it. If you adjust ti to much you can create a problem where the heater would come on with little pressure coming thru it and thus damaging the unit.
 
One of my replacement nozzles came today and I fitted it and the strangely customized nozzle that was in our bundle of pool stuff in the basement. After I turned on the pump, I was able to fire up the heater no problem (and it didn't turn off during the 5 minutes I let it run). Hopefully after I fit my 3rd nozzle when it arrives on Saturday that should provide enough pressure to keep the heater on as long as we need it. Thanks again for the advice
 
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