Heater Turns on for 15 Seconds then Shuts Off


New member
Jul 9, 2010
We have a two-year old pool with a MasterTemp 4000 gas heater. It had been working fine, but when we tried to heat the spa the other day the heater ignited, ran for 15 seconds then shut off. We have replaced the thermostat, a relay and the igniter, but the problem persists. Any thoughts?




Well-known member
Nov 6, 2009
Richmond, TX
Had the same problem with my variable speed pump. I had the pump running to low (~2,500 rpm). When increased to ~3,000 rpm, heater stayed on. The heater manual did say that low water flow will cause it to cut off.

Good Luck

Melt In The Sun

TFP Expert
LifeTime Supporter
Oct 29, 2009
Tucson, AZ
I agree that it sounds like a flow issue. It may seem like a dumb question, but are all the appropriate valves open? That pump should give you plenty of flow, unless there's a problem somewhere. Do you get decent flow at the returns?


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
I is possible that the heater needs to be cleaned. When the fire box vents get partially clogged by ash the heater will shutdown because it can't get enough air flow.


If you bought three or more Pentair products at the same time you are still under warranty. You should not have to replace the thermostat, a relay and the igniter already.

Sounds like you may have spider webs in the ports, or another build up. Did you pull the face piece and take a flashlight and look at the burner tray? I would take a look in there, as the fact that it is at least igniting tells me that everything is basically working.


TFP Expert
LifeTime Supporter
Mar 29, 2007
Coastalish 'down easter'
Welcome to TFP!!

Let me throw out my $.02 - check the thermal regulator, if it's shot cool water will not mix with the heated water and the temp will climb high enough to trip the high limit switch in ~ 10 - 15 seconds.

Of course there are other possibilities, you can 'jump out' any suspect switches, rather than just blindly replacing parts :cool:


LifeTime Supporter
Apr 26, 2009
I'm with waste - sounds like a limit switch problem. If you are handy with an ohm/voltmeter, look at the wiring diagram and ohm out the limit and pressure switches.