MasterTemp 400 (connected - RS485) short cycling

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Turbo1Ton

Turbo1Ton

Gold Supporter
Dec 26, 2019
1,995
NE Oklahoma
Pool Size
14500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Good morning!

Noticed an issue with my heater this morning. Heated the pool yesterday with no issues (that I noticed), and the wife sat in the spa for a bit last night and didn't mention any issues.

This morning we turned the heater back on to take the chill off the pool for this afternoon, and as far as I know, it has been working just fine. It was bringing the temps up from 83 to 88. I noticed it short cycling with the temps about 86. It is short cycling, firing for about 30 seconds, and then shutting off for about 1 minute or so, I'm guessing enough time for the blower purge to complete to attempt another ignition cycle.

I am not getting any alarms, with the exception of if I turn the heater completely off (unselect the heater, or lower the setpoint, not actually cycling power) I will get a brief Air Flow Alarm but it immediately disappears from the list as soon as I click the alarm tab to see them. I've also seen one that is something about ignition, but it disappears too quickly for me to figure out what that one is.

I have pulled the covers and looked at everything, no blockage on the blower intake or anything that looks suspect.

The connected Fenwall does not have any diagnostic LED's. I do not know if the new board has any LED's but I suspect it does not. I can check that.

Anyone know any reason these would short cycle like this?

As I typed this I realized I did not cycle the power, so I am going to go do that and see what that does.

Any thoughts on other things to check? I do not have a manometer to check gas pressures but with nothing having changed between yesterday and today I struggle to believe anything is wrong there. I would also suspect I would be getting an alert if gas pressures were low.

--Jeff
 
Short cycling is a water flow problem causing the heater to overheat. As soon as it cools down it fires up again.

  • Low water flow due to clogged filter or low pump rpm
  • Bad Thermal regulator
  • Bad bypass valve
  • Blockage in water manifold

Remove the thermal regulator and see if the heater works as a TEST ONLY. Do not run the heater like that.

Otherwise you have to remove the manifold to get at the bypass valve.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
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Turbo1Ton said:
Good morning!

Noticed an issue with my heater this morning. Heated the pool yesterday with no issues (that I noticed), and the wife sat in the spa for a bit last night and didn't mention any issues.

This morning we turned the heater back on to take the chill off the pool for this afternoon, and as far as I know, it has been working just fine. It was bringing the temps up from 83 to 88. I noticed it short cycling with the temps about 86. It is short cycling, firing for about 30 seconds, and then shutting off for about 1 minute or so, I'm guessing enough time for the blower purge to complete to attempt another ignition cycle.

I am not getting any alarms, with the exception of if I turn the heater completely off (unselect the heater, or lower the setpoint, not actually cycling power) I will get a brief Air Flow Alarm but it immediately disappears from the list as soon as I click the alarm tab to see them. I've also seen one that is something about ignition, but it disappears too quickly for me to figure out what that one is.

I have pulled the covers and looked at everything, no blockage on the blower intake or anything that looks suspect.

The connected Fenwall does not have any diagnostic LED's. I do not know if the new board has any LED's but I suspect it does not. I can check that.

Anyone know any reason these would short cycle like this?

As I typed this I realized I did not cycle the power, so I am going to go do that and see what that does.

Any thoughts on other things to check? I do not have a manometer to check gas pressures but with nothing having changed between yesterday and today I struggle to believe anything is wrong there. I would also suspect I would be getting an alert if gas pressures were low.

--Jeff
Click to expand...
Its that 86 degree reading that is a clue. Seems that when the thermister starts to fail most of the times I've seen it is at that temperature.
Top left side of the manifold, 7/8" wrench.
You can always get OEM, but I have used these for many repairs and not had any fail:
 
Turbo1Ton said:
Question is, is the Pentair part worth the extra money, or is a generic good enough?

--Jeff
Click to expand...
For your piece of mind, get what you are comfortable with. If I do a repair and the part fails quickly, I have to do it again for free. In only use parts that have a good record of not failing. Wholesale Sensors' stuff has work well for me. Not likely that Pentair actually makes all of the parts they use in their products, but outsource them, just like automobiles.
 
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1poolman1 said:
For your piece of mind, get what you are comfortable with. If I do a repair and the part fails quickly, I have to do it again for free. In only use parts that have a good record of not failing. Wholesale Sensors' stuff has work well for me. Not likely that Pentair actually makes all of the parts they use in their products, but outsource them, just like automobiles.
Click to expand...
Yeah, I generally don't like buying the cheapest, but if there are good aftermarket parts available, I am usually happy to try those.


Bought this one. About half the cost of the Pentair ones I found and as long as the photos are correct, it has the exact same PN on it. We shall see. Should be here tomorrow. I'll advise on longevity once time some time has elapsed.

--Jeff
 
Installed the new thermal regulator. So far so good.

I did finally get the old one to open. I don't remember at what temp water, 150-160 or more, and when it opened, it was creaking and popping as if it were bound up. I took it apart, and while I found some corrosion around the inside edges of it, there was no corrosion on any parts that slide together.

Oh well, it's replaced and I'll try and remember to advise on longevity of the aftermarket part, at some point in the (hopefully) distant future.

--Jeff
 
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