Pentair NT 400mv Heater problems

[poolmonkey]

I have an inground 30000 gallon plaster pool. The heater is controlled by a Pentair CP3600 controller. This heater only fires intermittently, sometimes when it does, it will only heat the spa to 93 degrees, other times it works fine and heats to 101 degrees. I find myself in a finger pointing session between the pool & gas company.

I was unable to reproduce the problem for the pool technician who asked to get the gas pressure tested. Gas tech readings are 12.5/11 (htr off/on)WC. Label on heater indicates Min Gas Pressure WC 12, Max Gas Pressure WC 14, Manifold WC 11. Gas technician can not set WC any higher as the control mechanism is "cranked as high as it can go" and says the manifold pressure is 11 WC when the heater is running.

Pool company is now suggesting the water sensor be replaced. Does anyone know if it may be cleaned. Any other ideas on how to debug since no error codes are visible from heater....Thanks in advance

[thepoolman1]

Are you sure that this is a millivolt (mV) heater?

There is no way to clean the water temp sensor. A bad sensor is, however, the most common cause of the problems you are having.

[poolmonkey]

An update for those interested.

I replaced the water sensor/thermostat and problem was still happening. Another call to the Gas company sent out a chap who debugged my problem. Since this was a Mv heater he said it got its current from the flame of the pilot light. With an ohmmeter we measured the resistance of the flow valve controller which was rougly 550. He thought that was a little low and took a look at the burner. After giving it a quick clean using some sort of air device the resistance was measured again and read ~750. The heater is now performing with no problems (touch wood).

Please ignore my electrical ignorance, I focused on Comp Sci. at college.