Pool / Spa Heater Seems to cycle Hot and Cold Water

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bongardjm

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Gold Supporter
Aug 12, 2014
51
Canton MI
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I have a MasterTemp 300 heater for our inground 25K gallon SWG pool w/ a raised spa. When in spa mode and heating the spa it seems like the heater will heat the water for about a minute and then we feel cold water coming through the inlets, then it heats the water, feels great when sitting in the spa, and then cold water for a bit etc..It does heat the spa up to desired temp eventually.
Just seems inefficient? Why wouldnt it just heat contiusously to set temperature. Seems like it would heat faster?

PB says that is by design as Pentair does not want continuus heat and cycles the heat for liability reasons. i.e no scalding burns I guess when your in spa and it is heating at full balst for extneded periods?
Does anyone else expereince this or should I be concerned?

Thanks!
 
Well it is not heated, so it feels colder?? , my guess is it is just not heated and maybe losing some heat going from spa to heater and back. The heater seems like it is always on, but is some how set to only heat in cycles and not continuously. I would hope it is not pulling from pool as it is in spa mode and is only pulling and sending to spa.
Everyone who is in spa notices. They state "hmm, thats odd I feel cold water" coming through the jets.
 
Welcome to the forum :wave:

I went through the manual and it isn't covered that I could find. My electric spa heater and older LP pool heater both heat until the set point is reached. I don't know if that's the same for yours but I don't really understand the scalding issue as the heater shouldn't be able to heat the water that much considering the small amount of time the water is in the heat exchanger and the large amount of flow. That's the reason they have such a huge BTU capacity. It takes a lot of fuel to heat that water when it's moving that fast through the heater.

It's just a seat of the pants guess but it sounds like you might have low flow or the heater is "seeing" low flow and it is getting too hot or thinks it is and a safety is shutting it down and then restarting it. Could be the burner high limit is set to low or it's defective or you have a flow restriction. To me it doesn't make sense it would cycle on and off as it's trying to get up to your desired operating temperature. I'm guessing when you are in the spa the water coming in when the heater first kicks in is almost the same temp (feeling it in the spa) as when it kicks out.

I'd call Pentair and see what they say.
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That does sound odd. Mine would heat for a good bit of time (much more than a minute) until it reached temperature and then would recirculate and slowly the water would cool down until the heat kicked back on. But, certainly never felt cold water entering.

I am wondering if you are not fully closing off the suction to the pool? If you run it is spa mode are you sure that any overflow to the pool stops?

Still bizarre that the heater might cycle that often though.
 
I like the suggestion of a flow issue and that is getting too hot. The pool suction suggestion is interesting, but even if I was pulling pool water along with the spa water it would still be getting heated?? and their should not be such a sudden change in temperature...one would think.
However I may take apart the valve tops to see if truly when in spa mode it is fully closed to the pool.
On a side comment...this is by far the best site and responsive members I have ever seen. I feel so educated going through this site and am able to talk to my PB with confidence! Thanks TFP!
 
Stand by the heater as it is running. You should hear the heater light and feel the heat coming from the exhaust chimney while it is burning. If during the heat up cycle, the unit stops heating and then suddenly starts ups again, there is an issue. The heater should stay lit up till the water reaches the set temperature. It is a constant heat cycle. It doesn't cycle the heat up. Just like a house AC or furnace, it heats till the temperature you set it to is reached. If while it's heating, you get the LED lit for Service Heater, you would need to look under the top of the unit to see what other LED is lit. If the Service System LED comes on, then you have a water flow issue. Other reason why the heater could cycle while heating could be a bad thermo regulator.
 
So I stood next I to the heater and watched the spa heat up. It was a continuous flow of heat, worked great until around 90 degrees then it would say service heater and turn off. Few minutes later it would turn on and cycle hot water and then turn off. This just continues. I opened the heater and saw error code 'HLS'

I remember a post about flow. I have a pentair VS high efficiency pump. Normally when I run spa I set it at 2350 RPM. On a whim I jumped it up to 3150 and the heater worked great, never cycled.

So is it a flow issue, should I be able to run the spa at 2350 RPM? I'm going to call PB as pool is only 3 months old. Seems like the only solution is to Max out the pump when heating the spa, seems like a bad solution though. The spa is raised above pool, could it need an adjustment to pressure setting?
 
No pressure setting change needed. The only time a pressure switch change is needed is a case where the spa is setup much much higher than the heater and when the unit keeps running when the pump is shut off and the pressure of the water causes the heater to stay on. In your case I wouldn't change anything on the pressure switch. So the heater is as old as the pool correct? I wonder if the thermo regulator or the high limit switch have issues. It's easy to check the thermo regulator but if the unit is new, get a Pentair service company involved so you don't void the warranty.

Running the pump at a higher speed is OK. With the variable speed pumps coming onto the scene has caused many issues with heaters.
 

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I have the PB looking at it today. It has done this since day one of going live with pool. As a new pool owner (opened since July 2014), I just thought it was normal, until everyone who sat in hottub kept asking why cold water? Well we shall see what they find...On a side note running the pump at 3150 RPM and being in hottub was great, worked liked a charm. Just concerned that it is covering up the problem and that I technically should be able to heat spa at a lower RPM. I would imagine at 2350 RPM I am pushing more than the minimum 40 GPM that my heater requires, I could be wrong though I guess. Just my OCD side coming out...
 
PB took out old thermo regulator and it is all corroded and wont slide very well. Replaced and problem solved, worrks like a charm. Now I need to determine why within 4 months it went bad. PB says it is usually due to low PH. I check PH everyday and ensure it is good. Keep it at 7.5. It is a salt water pool. I will keep an eye on this one though. Thanks for all your help
 
I don't but it looked like a solid ring of dark red rust with green dots on it, it was obvious it would not slide well. Its only 4 months old so it is concerning.
 
Seems very odd. Did the PB do a initial pool start up with you and make sure the chemicals were good before turning the pool over to you? Also, what do all of your water readings look like? Also if you recall, did they do all the initial chemicals with the pool heater hooked into the plumbing or had they installed a bypass to keep the heater isolated? I'm asking becasue it would concern me if the heater was running water thru it if the water wasn't balanced. You could have other issues on the horizon.
 
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