Heater cycles on/off without heating

ratzfatz

Member
Sep 24, 2021
21
Menlo park
Hi All, I have a pentair system with intelliFlo VST and master tem 400. I had to install a nsw subpanel and so needed to wire my pool to a new breaker. Since then the heater act weird it heats very slowly as it continuously turns on and off. Everything else is normal. The pump runs at 3000 RPM/41 GPM the pressure valve on the filter is normal. The heater shows no warning light.
I cannot imagine why changing the breaker could trigger this but it is suspicious because it right happened after changing the electrics.

Also I tried to open the thermal regulator to check it but i cannot open it. I almost broke my screwdriver but it would not open.

Thanks!
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,091
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Welcome to TFP.

I think the subpanel and breaker change are a coincidence to your problem of the heater short cycling.

Short cycling is often caused by a low flow rate. How are you measuring 40 GPM @ 3000 RPM? That is a low flow for that speed and just at the minimum flow rate as specified on page 14 in https://www.pentair.com/content/dam...stertemp/Manual-MasterTemp-472592-English.pdf

When was the last time you cleaned your filter?

What model filter do you have?

What is your filter PSI?

Other reasons can be:
  • Thermal regulator not opening.
  • External bypass open.
  • Internal bypass broken.
  • Pump too small or on too low rpm.
  • Clogged filter.
  • Scale in heat exchanger.
Start by checking the thermal regulator. If you can't unscrew the thermal regulator you may need to remove the manifold which will let you check the thermal regulator, internal bypass, and heat exchanger. If the thermal regulator can't be opened there is a good chance the regulator may have problems.

 

ratzfatz

Member
Sep 24, 2021
21
Menlo park
Hi you are right with the low flow rate. I actually configured the vsf pump to 50 GPM but it would only manage to do 41gpm at max rpm (i put in a limit at 3000rpm). I have 2 inch pipes everywhere so I would have expected more. I will open the chassis tomorrow and have a look at the thermal first. Flow rate/rpm is measured by the screen logic intelliscreen. The filter has been cleaned 3 month ago. It is a big pentair thing

 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,091
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Find the restriction in your system causing the low flow rate. Your pump should be flowing more with the setup you describe.
 

ratzfatz

Member
Sep 24, 2021
21
Menlo park
I checked all filters everything is clean. Then I configured the cleaner to run at 60 GPM and I could reach 60gpm with 2800 RPM. The pipes from the filter outlet directly goes into the heater. I assume that in filter mode the inner bypass of the heater is used and that it permits 60gpm, but in heater mode flow is restricted to 40 GPM and I have this on/off cycling. So it must be the heater not the pump
 

ratzfatz

Member
Sep 24, 2021
21
Menlo park
With a utility knife and some heavy tools I could remove the thermal regulator. It has green oxidation on it but when putting it under a sink it extended. I don't have a thermostat to see what exact temp I am using. Should I replace it nevertheless?
 

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Poolbreh

In The Industry
Jul 31, 2021
272
San Diego
it’s a flow issue like Allen mentioned above. Minimum flow is 40gpm for mastertemp 400. Something isn’t adding up with your rpm and gpm.
how are you measuring gpm?
How far is pool from equipment?
How high is pool from equipment?
What does the status of vsf in settings say?
1632597273678.jpeg
 

ratzfatz

Member
Sep 24, 2021
21
Menlo park
it’s a flow issue like Allen mentioned above. Minimum flow is 40gpm for mastertemp 400.
But i am getting 60 [email protected] RPM when bypassing the heater. Isn't this a clear sign that the heater is the issue?
Something isn’t adding up with your rpm and gpm.
how are you measuring gpm?
- intelliFLO status on easytouch
How far is pool from equipment?
20 feet
How high is pool from equipment?
Equipment is on ground
What does the status of vsf in settings say?
View attachment 374135
 

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Poolbreh

In The Industry
Jul 31, 2021
272
San Diego
I feel you should be getting closer to 100+ gpm at 2800 rpm bypassing the heater, it’s normal to get a drop in flow when running through exchanger. But you are still barely at the minimum requirements. The video isn’t showing.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,091
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Those GPM flow rates from the pump display or EasyTouch are a calculated amount and not an actual measurement. I would not put much accuracy in the displayed GPM. To know the real flow rate you need a flowmeter in your plumbing doing actual measurement.

Are you running the pump in RPM mode or GPM mode?
 

ratzfatz

Member
Sep 24, 2021
21
Menlo park
Ok makes sense. I unfortunately cannot measure the flow rate more accurately than via easytouch. I configured it in GPM mode to 100 GPm and the maximum it would do at 3000RPM was 63. I am looking at where the water drains to the equipment and it indeed looks weak to me I would have expected to see more water draining
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,091
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Try running in RPM mode at 2000 to 2800 RPM.

I have an IntelliFlo VSF pump with a DE filter and a MasterTemp 400 and my MasterTemp will run as low as 1700 RPM although I usually run it at 2400 RPM.

You should not need the pump speed you say for the equipment you describe.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,387
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I cannot find where you told us what type of filter you have. If a cartridge filter, remove the the cartridges and see if the flow rate improves. If a DE or Sand filter with a MPV, set at recirculate.
 
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