Our pentair400 natural gas heater (2000 gallon in-ground spa, filter pressure under 20PSI) lights, heats for 30-40 secs, shuts down as if the set temp has been reached (has not) then after 90 seconds the unit restarts, relights and repeats the cycle until set temp is reached. From new (2 years old) the unit never heated nonstop until set temp, but would heat many more minutes before cycling off then back on again. The unit was intentionally oversized by the spa company so it would heat quickly. ? clogged heat exchanger with lower flow, ?stack flu temp sensor? Thoughts?
Pentair Heater lights, heats 30 seconds, shuts off, restarts in 90 secs, repeats
- Thread starter sholdr
- Start date
What is the exact model of the unit? Pentiar has several units under their name.
If this unit acted this way since day one, then I suspect an install issue. Did you ever address this with the installer or Pentair for that matter while it was under warranty?
If this unit acted this way since day one, then I suspect an install issue. Did you ever address this with the installer or Pentair for that matter while it was under warranty?
Model 460738. Was assured the cycling was normal for a pool this small and heater this big -- now out of business.....Cycling now much more frequent but still eventually heats to set temp
Sholdr
I'm going to guess that the model is a MasterTemp heater. The model number you provided relates to a part on that heater.
First make sure you have adequate water flow to the unit. Make sure if you have all vales set correctly if you have any. Then the next thing I would check is the bypass valve in the unit and the thermal regulator. The thermal regulator is most times the culprit in this type of issue.
First make sure you have adequate water flow to the unit. Make sure if you have all vales set correctly if you have any. Then the next thing I would check is the bypass valve in the unit and the thermal regulator. The thermal regulator is most times the culprit in this type of issue.
I have experience with a much older heater and any time I have had issues like this it was due to the gas flow being restricted due to a dirty burner assembly. After removing and cleaning the burner assembly the unit works great.
If this is a MasterTemp heater, the burners are in a sealed can and to clean them is a huge major task. Cycling is an indication of water flow issues.
Is a mastertemp as you surmised -- will investigate your suggestions -- THANKS.
Will report any progress
Thanks for the help -- Removed the thermal regulator and indeed does not open when put into boiling water.
In addition found the bypass valve plastic piece not held up by it's spring -- on removal of the thermal regulator this plastic valve came down and out. Briefly ran the pump with heater outflow disconnected to flush out of the heater any debris, reconnected the outflow and tested the system -- worked perfectly for the first time since new heating without cycling even once and shut off appropriately and restarted no problem when I advanced the set temperature. I assume the missing pieces are there for a reason, but any ideas what the down side would be to leave well enough alone? Perhaps keeping the heat exchanger warm between cycles to decrease condensate in the can?
I do not mind the effort to replace the pieces -- I removed and had repaired the heat exchanger on our prior heater -- the installer did not use the more salt-resistant model.......lasted 3 more years...But since it now works better than day 1.....
Thanks
In addition found the bypass valve plastic piece not held up by it's spring -- on removal of the thermal regulator this plastic valve came down and out. Briefly ran the pump with heater outflow disconnected to flush out of the heater any debris, reconnected the outflow and tested the system -- worked perfectly for the first time since new heating without cycling even once and shut off appropriately and restarted no problem when I advanced the set temperature. I assume the missing pieces are there for a reason, but any ideas what the down side would be to leave well enough alone? Perhaps keeping the heat exchanger warm between cycles to decrease condensate in the can?
I do not mind the effort to replace the pieces -- I removed and had repaired the heat exchanger on our prior heater -- the installer did not use the more salt-resistant model.......lasted 3 more years...But since it now works better than day 1.....
Thanks
You have to replace the bypass valve or water can flow without going thru the unit. So replace the bypass and the thermal regulator. When you do this, you also should also get a o-ring kit and replace them as well to prevent any leaks.
No such thing as a "more salt-resistant model" heater. The amount of salt used in a pool is nowhere high enough to cause any issues in the heater or pumps.
No such thing as a "more salt-resistant model" heater. The amount of salt used in a pool is nowhere high enough to cause any issues in the heater or pumps.
I really do appreciate your educating on this blog, and not to belabor the point, but if the missing bypass valve now cut water flow thru the coil sufficiently to be a problem the heater should not heat the spa as quickly as it does now and the temp limit switch should stop the heater as it apparently was doing with the stuck thermal regulator blocking flow. Normally the bypass valve opens to let through the excess flow until the thermal regulator opens after which the bypass valve can close partially or fully to ensure sufficient flow through the coil.......Perhaps from new the bypass valve was faulty so the heater cycled due to insufficient flow through even the functioning regulator valve, but with the regulator valve out the flow is now sufficient to cool the coil to prevent the high temp cutout......But why need a "thermostat" at all other than it would take a while to heat the coil on startup otherwise and perhaps on cold days lead to condensation and faulty firing.....
I will proceed with repairs as suggested
Thanks
I will proceed with repairs as suggested
Thanks