New member
Sep 17, 2015
Port Jeff NY
Hello All,

I know there are many threads re this issue but here goes...

I have a Mastertemp 400 natural gas heater that was winterized in perfect working order at the end of last pool season. Attempts to start it up this year has resulted in the heater starting as usual and shutting down after about a minute with an E05 error on the touch panel. The SFS light on the board is also on when this sequence occurs.

So far:
new SFS installed
new thermal regulator installed
new high limit switch installed
new thermistor installed

All wiring is in good shape and all contacts were cleaned and checked
no debris, nests, cobwebs, etc. throughout the unit
blower fan fully operational with good intake/exhaust

Temperature probe at exhaust near SFS goes up to 320 degrees and holds there until it shuts down and reads E05
Touch panel works fine in all respects
Pressing "pool" while running does not yield an exhaust temp but shows 80 and briefly 40 when held.
Alk and Ph are have pretty much always been kept in range and flow is good.

I am considering buyin a new control board before calling someone in....Thoughts?


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
E05 errors are due to things like a sooted exchanger (fuel delivery, venting), scaled up exchanger (water side), or a low water flow.

  • Sooted exchanger(external) due to improper gas pressure or lack of proper venting. either supply of fresh air or exhaust, or both. Heater is being starved of air and the resulting air/fuel mix is too rich (fat).
  • Calcified exchanger (internal) due to improper water chemistry. Note: Not necessarily right now, but at some point in the past, and for a while. This does not happen overnight.
  • Flow or velocity issue. Water is moving too slowly through the exchanger, gathering or absorbing too much heat, and is not carrying it away quickly enough to keep the heater at a workable temp. In this case, you may have a valve closed down, but not fully closed, or may be wanting to save a little more money on your electricity bill, so you turned down your VS pump as low as you can get away with. You will need to turn it back up to correct this !
My bet is that your problem is one of these three causes.


TFP Expert
Mar 2, 2011
If you hold down the "pool on" button, it stays on 80, then flashes to 40, then back to 80, then the 80/40 reading and E05 indicate that the board is not getting a reading from the sensor. It's usually a bad sensor or damaged wires.

If the sensor and the wires are good, then the board is probably bad.
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TFP Expert
Mar 2, 2011
Thread Status
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