Master temp 400 service system light

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Kevin y

Member
Jan 15, 2022
11
Dallas
My Pentair master temp 400 heater will not turn on.

If first started by cycling on and off frequently and now the service system light is on.

The PS led on the board is also on. I have checked the Pressure switch and even jumped it out and the PS light will not turn off.

Flow rate is good, filters are clean.

Anyone know any thing else to try?
 
Welcome to the forum.
Review Pentair MasterTemp Heaters - Further Reading for some trouble shooting ideas. Typically the first thing to look at is thermal regulator. But your issues do not present as the normal items caused by that part failing. But it is easy to get to and test.
 
mknauss said:
Welcome to the forum.
Review Pentair MasterTemp Heaters - Further Reading for some trouble shooting ideas. Typically the first thing to look at is thermal regulator. But your issues do not present as the normal items caused by that part failing. But it is easy to get to and test.
Click to expand...
Thank you for the suggestion. Thermal regulator tested as good.

However I did find the bypass valve stem floating around when I removed the thermal regulator. I ordered a new bypass valve kit. Hopefully that will solve the problems.
 
Get the gasket and O ring kit to replace them when you remove the manifold.

Find all the pieces of the broken bypass valve. One of the pieces may be somewhere in the plumbing causing the PS issue.
 
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The "Service System" led is usually an indication of a flow problem and not allow the heater to fire, the broken bypass would show up as other issues if the heater were to light (ags, hi-limit errors and a lot of banging). That would show as a "Service Heater" led (That led lights every time the heater fires as part of its self-check). If you jump the pressure switch and the heater still fails to light, be sure there isn't rodent damage to the wiring (they love these heaters). If there isn't, likely you will need a new PCB. The pressure switch is the first or second item the self-check looks at before allowing a heater to attempt to try to light.

I've seen those bypass valve stem missing in many systems and they were never found, probably stuck in the plumbing somewhere. They have never caused a pressure-switch issue in my experience
 
Thanks everyone. After replacing the bypass valve the problem still existed.

I doubled checked the voltage on pressure switch.

Final result. Control was bad. Just replaced it and all is working great just in time for the big Texas snowstorm!
 

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With rodents in your heater I suspect your E05 error is more then a sensor.
 
Yes. Maybe I missed something but everything in the document seems to be checking out ok.

Odd that the heater runs fine until the water temp hits 78 degrees.

I even switched to heating the pool for a couple hours and the heater kept going with out any problems.
 
Heating the pool up to what temp does it run on?

  • 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 !
Check the interior for obstructed venting (intake and exhaust). Animal nests, spiders, mud dauber nests against the air blower vent, can all block the air flow and lead to an overheat and SFS error.

You see those problems a lot more then a sensor that has gone bad. Although continued high temps could eventually cause a SFS to fail. The SFS will let the heater stack temp to run up to 480 degrees before it will shut the heater down. In the case of a sooted exchanger, the stack flue temp would rise slowly over time (weeks/ months) subjecting the sensor to extended over temp conditions.

The sensor may be tested with an ohm meter (3.8 MegOhms @ 77F) If you decide to get a new SFS, check the stack flue temp when you get it back together and running to confirm that the stack flue temps are where they should be, and not too high.
 
Kevin y said:
We have the easy touch remote.
Click to expand...

You have five temperatures to report for your heater problem…
  1. Water temperature displayed on ET
  2. Heater set point on ET
  3. Water temperature displayed on MasterTemp heater
  4. MasterTemp heater set point
  5. Actual water temperature in spa or pool as measured by a thermometer

What are those five temperatures as the pool/spa gets to 79 degrees?
 

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