Master Temp 400 ERR SFS Just the Sensor?

[JamesW]

I think that it is a flow issue.

If you have good flow, this check valve flapper should be open wide.

 

[W.J.Christy]

You are correct, in that pic the bypass is open. The heater wasn't on in those photos. Curious if its a flow issue as it was functioning fine about 2 weeks ago and also when i tested the bypass back around easter.

Not sure if it makes a difference but the bypass is set up to still flow through the heater when open to help maintain a proper chemistry and help during freeze protection mode. That flap opens wide once the bypass is closed.

 

[W.J.Christy]

Pic of the flap when the bypass is closed and heat demand is present. Also pic of the menu. The temp rise was fast. Like sub 60 seconds.

I have increased the rpm of the pump. Going to let the heater rest then try again with the higher rpm.

 

[W.J.Christy]

Welp, checked the resistance of the sensor, it was 2.34 mega ohms. It appears its bad.

 

[JamesW]

Can you show the valve with the bypass closed?

 

[JamesW]

Does the water temperature on the display also go up rapidly?

Yes.

If the water temperature is going up fast, then that indicates a flow problem.

 

[W.J.Christy]

Bought a Amazon sfs as a just in case and tossed it in after checking the oe one. The heater is operating correctly and the stack temp appears to have leveled off at 300F.

I couldn't help myself but open it up. The engineer in me made me do it.