Mastertemp 400 cuts off

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This is the way that the valve handle needs to turn for heating.

The red dot is where the handle says "OFF".

The Brown check valve might not be working correctly causing a lack of flow.

If you have a lack of flow, then the heat is probably backing up into the inlet causing the water temp to read higher than the set point.

Does the water temp reading suddenly increase when the heater fires?

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ParrishGuy said:
One thing to note is the pressure on the filter canister goes from 8psi to 20pai when the heater is not bypassed
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I suspect that the check valve is probably defective.

If the heater shuts off with no indication of error, the likely cause is a water temp reading going above the set point due to heat backing up into the inlet.
 
JamesW said:
I suspect that the check valve is probably defective.

If the heater shuts off with no indication of error, the likely cause is a water temp reading going above the set point due to heat backing up into the inlet.
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I think we're definitely narrowing this down. I just looked at the panel and model is MT 400 LP so I'm 99% sure its propane without taking the orifice out to look at the size of the hole. It also operates very quietly and I've read if it was a NG on LP it would "scream like a banchee"

Also, I think I'm going to take off the manifold tomorrow and check that internal bypass again because there is a rattling sound and maybe I didn't know what I was looking at when I took it apart two years ago. I think it's either the internal bypass or that check valve not letting enough flow through. I do have that diverter turned the other way you pointed out to have it when the heater is in line and running. In that old picture it was bypassed and I knew that.
 
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JamesW said:
That is 12 psi, which is too much.

Pentair lists Heater Head Loss as about 7 feet, which is 3 psi.

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Alright so here is the latest today. The internal bypass was in perfect condition. The sensor you see in the picture had some corrosion but ohm'd at 9.0, I cleaned it up w some sand paper. I took a hose at full pressure and put in each one of the holes in the manifold and they all flowed out the other side perfect with no obstructions. I'm thinking that bypass/check valve may be causing back pressure not letting enough flow like you suggested. Do you have any ideas on placing an open piece of pipe in its place for testing purposes? See attached pictures..
 

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ParrishGuy said:
The sensor you see in the picture had some corrosion but ohm'd at 9.0, I cleaned it up w some sand paper.
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That is the 10K temperature sensor and should read more than 9 ohms.

Temperature Sensors - Further Reading

www.troublefreepool.com www.troublefreepool.com

10K_thermistor_chart.png


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ParrishGuy said:
Would that thermistor showing low ohms cause short cycling?
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The heater should read a high water temperature and not run at all.

Is the water temperature correct on the heater display?
 

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