New thermistor - still won’t hold temp

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Bketchum5

0
Jun 17, 2018
56
edmond,OK
Pool Size
25000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I recently had a clanging and knocking and rattling noise when my heater was trying to kick on. I found the thermistor was bad and wouldn’t open causing the pressure of the water to make the spring rattle like my heater was about explode. After replacing the thermistor no more banging and knocking. However, the heater still doesn’t seem to hold heat. It will get to 90 degrees, gas will shut off and gas will kick back on as the spa won’t reach set heat temp. Ill
Hold the spa on button down to see the internal temp and as soon as it hits a number it immediately starts dropping, gas kicks off then kicks on again and again. Any thoughts as to what might be the next step?

Mastertemp 400
 
can you post pics of the plumbing leading to the heater? It sounds like a flow issue. The heater needs a minimum of 40gpm to operate properly. Make sure filter is cleaned and vs if you have one is set to perform 40gpm or more. When the heater shuts down do you get a sfs light on the back of the board?
 
Poolbreh said:
can you post pics of the plumbing leading to the heater? It sounds like a flow issue. The heater needs a minimum of 40gpm to operate properly. Make sure filter is cleaned and vs if you have one is set to perform 40gpm or more. When the heater shuts down do you get a sfs light on the back of the board?
Click to expand...
Like the gas plumbing? The gas pipe runs down the side of my wall from meter about 35’, 90’s about 3’ to the mastertemp

Just cleaned my filters. Was doing this before and after cleaned filters. The thermistor fixed the banging noise. It was basically stuck due to scale or rust looking. No service lights come on.

I did literallly just fix and air leak after months of replacing o rings, shaving cream, etcetera. I really don’t even know how I fixed the air suction. Dumb luck I guess.

VS is set to 3400 rpms. How do I change the
 
Replacing a thermistor wouldn't make a noise go away. Apparently Mastertemp 400s (I have one, too) can have problems with bypass relief valves breaking. Check out this video
. What you say would be consistent with the valve breaking, rattling around for a while in the flow, and finally getting loose into the plumbing at the same time you replaced the thermistor. Now it's sitting somewhere in the return plumbing blocking flow, which will cause the heater to act as you say.

This is just one theory. But it will be pretty easy to check out. Remove the heater manifold to see if the valve is gone!
 
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Sorry. I meant replaced regulator not thermistor. It was corroded looking and stuck. When i replaced that the banging and cleaning stopped but gas would still kick off and on like the heat was meeting the set temp then so on and so on. Maybe the bypass switch where water flows in is messed like a video I saw in another post
 
generessler said:
Replacing a thermistor wouldn't make a noise go away. Apparently Mastertemp 400s (I have one, too) can have problems with bypass relief valves breaking. Check out this video
. What you say would be consistent with the valve breaking, rattling around for a while in the flow, and finally getting loose into the plumbing at the same time you replaced the thermistor. Now it's sitting somewhere in the return plumbing blocking flow, which will cause the heater to act as you say.

This is just one theory. But it will be pretty easy to check out. Remove the heater manifold to see if the valve is gone!
Click to expand...
I’m thinking this might be the issue. But I didn’t have any service lights come on.
 
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So I found that little black thing in my return line from my heater when I unscrewed my SWG so I now now that’s what needs replaced. Still a little rattling noise but is that because the sling is loose in there until I replace it? Temp still won’t hold but I assume that’s because the bypass isn’t restricting flow. I’ll try to record a sound of the knocking
 

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