MT 250-Runs short time, powers off, no codes or lights, motor runs

[Dalancas]

Time for my annual issue with this MasterTemp 250 heater. ;-( This is strange, never saw this problem before and couldn't find it replicated by anyone in my TFP search.

Water flow is good, no issues there. Heater was working great for many months now. But, all of a sudden when it turns on manually it will run and heat for 10-30 seconds and normal Heating light blinks and stays on once lit--then it ALL turns off. NO Service lights at all. NO LED lights on backside at all. BUT, the blower fan will continue to run to cool it for 30-60 seconds then turns off.

No codes, LED, service lights, nothing. It just stops heating and turns lights off, then eventually fan off and it will not come back on unless I manually turn on, then it cycles through the issue again. Cant keep it running and I have reset power and power codes are fine. It just wont stay running and heating.

Ideas to check?

 

[JamesW]

I'm thinking that it's probably a bad membrane pad. I would replace that first.

If that doesn't work, I would replace the control board.

 

[Dalancas]

UPDATE:
I wanted to provide an update on this issue so it may help others. The bottom line fix was to remove all connectors on the control board and clean all corrosion on pins and reassemble.

I went through and pulled all the safety switches to ensure they were not the culprit, although I had no lit LEDs on the control board nor in the ignition module. The heater just turned completely off, so no clues to where problem was.

I cleaned the stack flue sensor with fine sandpaper, good as new. I cleaned up the sensors in the manifold as well and while there was light corrosion they looked to be in good shape.

Pulled the lower and drain plugs and cleared some of the built up muck out but nothing real bad there. The plumbers putty had hardened and was a PITA to remove but all good now for another few years. I last had this heater apart 4 years back to replace the coil with a nickle copper coil.

Traced all wires to ensure they were not chewed on, and while I have had rats living inside they have not yet done any damage to the internals of the heater.

Lastly, I removed and replaced the membrane board connection several times onto the control board in the event it had a poor connection.

All this had no effect. I could still start the heater and it would run for some number of seconds and then all lights went out, flame went out and blower would shut off ~40 seconds later. Press the Pool or Spa button yielded same results.

SOLUTION:
So, I pulled all connectors from the control board and carefully sprayed with dielectric fluid to help remove corrosion on the pin connectors on the board. There wasnt any real noticeable corrosion but things get dry here in the desert so I suspect it was light buildup that causes some corrosion or fretting on the connections. Apparently that is what has happened.

I plugged everything back in and have not had any issues at all. I have shut the heater down, started it back up in Pool and Spa mode and it is good as new. Even set it to 101 last night for a relaxing soak, and no issues. It started up fine this morning and has already cycled on and off as the temp falls/rises based on thermostat setting.

I will keep an eye on things and ensure the control board is not slowly going to die an eventual death soon. Will report back here if I find any anomalies.

But, I would caution anyone to throw out that control board or membrane pad without cleaning the connections and trying that first. It can save you some serious coin, potentially as it did for me.

 

[JamesW]

I still suspect that the membrane pad is probably going bad.

 

[Dalancas]

James, (and others) let me know what you think.

Since cleaning of the connections and sensors, all was well for a week and a half. Then I start seeing the heater stalling at power on on the AD0 code. I referred here to see I had this trouble in August 2018--heater turned on to AD0 code and fix eventually was to ensure AD set to 1 and SF set to 1, to match. Took multiple tries before it took, but eventually it did.

I just reset both AD and SF to value of 1, and heater seems to run okay for now. But, what would cause the heater to lose its memory/mind and forget the AD/SF settings?

I suspect maybe voltage line surge/sag/brownout, but just a guess. What have the pro's seen with this?

 

[JamesW]

I still suspect that the membrane pad is probably going bad.

 

[Dalancas]

Yes, I am going to order one and install and see what happens. Just went out to check and heater is shutoff with AD1 on the display. Perhaps a slow death. I have never replaced the pad, only the main board, so after 5 years its probably due.

Will report back once I replace it this week.

Thank you for your wisdom!

Dennis