MasterTemp 400 Heater won't stay running

[sturnpaugh]

I'll start by saying I have read through all the posts on this type of issue that I can find and have tried just about everything noted in them. I have a 4 year old MasterTemp 400 that is very rarely used. This past weekend after cleaning my filter I turned on the heater just to try it out before I start needing it (I live south of Houston and won't really need this for another month). The heater fired up normally and I thought all was well. I finished cleaning up and forgot about the heater being turned on. I remembered it about an hour later and went out to shut it off and found the Service Heater light on. The control panel was locked up and would not let me turn off the heater. I had to turn off the breaker to regain control of the control panel. As soon as the breaker was turned back on the heater started back into its start up cycle. After going thru the normal startup routine the heater again fired up normally, ran for 20 seconds +/, tripped the service heater light and locked up again. I looked at the back of the control board and found the AGS light on.

After going through the cycle a few times I see the following pattern.
1. Turn on the heater (either "pool on" or "spa on"
2. Everything starts normally
3. The instant the gas valve opens and the ignitor fires, the Service Heater Light comes on.
4. The heater continues running normally for approximately 20 seconds, definitely heating, hot exhaust for entire 20 secs,
5. Heater shuts down, AGS light illuminates, panel locks up

What I have tried.
1. Checked thermostat - it works open and closes freely under hot top water. Heater functions exactly as above without thermostat installed at all.
2. Checked bypass valve - appears fine, completely clean
3. Checked internal condition of header - all appears clean
4. Replaced AGS switch - no change in operation
5. Looked at Gas regulator (Itron B42), have not disassembled but vent is clear
6. Flow rate seems fine, discharge into pool and over spillway from spa is at its normal high rate
7. Filter is clean and filter pressure is at its lowest rate as always just after cleaning, so a blockage is unlikely


I would love some suggestions. Thanks in advance.

 

[ps0303]

Seems like you have followed all the steps of troubleshooting. Looks like you have a bad control board. Search around on the net for an inexpensive board and replace it.

 

[sturnpaugh]

Thanks PS0303. I was afraid of that. I thought I might jump out all of the safety switches first just to make sure. What is the best way to do that? Do I just short the two connector wires together?

 

[ps0303]

Yes that is correct. However, if the AGS LED is still coming on after you replaced the AGS sensor, then the board.

 

[sturnpaugh]

Ps0303,

I jumped out the sensors and confirmed the continued issue, but I have new wrinkle. When I checked the header before the lower left bolt head was corroded to the extent that it could not be removed...the bolt head was nearly gone. But I removed the other nine bolts and found no water. The remainder of my header inspection was done through the inlet and return ports, and everything was spotless. Since there was no water coming from any of the other nine bolt holes I assumed the coil was OK and, figured the bolt corrosion was from something else. However, this morning while checking the jumped out sensors I noticed water dripping from that bolt, and confirmed it is coming from around the bolt. I assume this means the coil is leaking? Could this cause the AGS shutdown? Or do I have two issues? ..corroded, leaking coil & bad control board?

 

[ps0303]

Taking out either of the lower bolts would let you know if you have water inside the unit. I see many of the bottom bolts in the shape yours is in and there is no water inside the unit. Could water inside cause the unit to pop the AGS LED? Possibly. But if you leave the bolt out and the unit still shuts down with that error then you still probably have a board issue. For commercial accounts I have removed the bottom bolt and left it out till I could replace the unit and the unit ran fine as the water was constantly draining.

 

[Panelpro40]

Everyone must be doing better then I am at the moment. Pentair Master 400 , it turns on and has large “ baroom” firing, just takes multi short runs , waters hot , starts heating tub, then water cools unit turns off, then minute or two later, “baroom” fires up again. Does this on and off continuously. Slowly working towards the set temp of 103’ . is it not supposed to be on until it gets to set temp?