Pentair Minimax Plus 400 hard starting

[mjohnson003]

I have a Pentair Minimax Plus 400 heater that is not starting up properly, somewhat intermittently.

When the switch is turned on, or the temperature control knob is turned up to call for heat, sometimes it will fire up properly, but sometimes it gets stuck before it actually fires.

When it does not fire properly, here is the sequence of events:
1) Switch turned to pool (or spa), or temp control know turned up
2) Click heard.
3) Thermostat LED lights (TSTAT) - so that seems ok
4) PowerMax fan turns on, AUX and PRESS LEDs light - so it seems that is ok
5) Heat LED never lights, and you do not hear the burners ignite, nor any clicking.
6) Service LED lights



The switch and circuit board have been replaced, and all wiring disconnected and the terminals cleaned, but the problem persists.

I did notice two scenarios where it seems to work properly.
1) If the heat has been on for a while, and I shut it off using the switch or the temp knobs (for a few seconds to few minutes) then turn it back on, it almost always fires up
2) the second scenario is, if I tap the panel that the controls are on, just to the right of the controls, it will almost always come on. I know that is where the gas control module (PN 073584) is located, so was wondering if that could be the culprit? I don't have to tap very hard, and usually once will do it, so am wondering if that module has any mechanical parts that could be "sticking"?

This makes me think it is an issue with the ignition circuit - either the control module or the ignitor.

Is there something else I should look at before replacing the gas control module (they are kind of pricey).

Thanks!

 

[cowboycasey]

While I do not have a heater and have never dealt with them, I can say this.. Those igniters are a pain, they just stop working, some more than others.. I wish I could tell you that if you replace it that it will work but I am not sure, but from what you're saying it sounds like that is the culprit

 

[ps0303]

How long ago did you replace the thermostat board?

Here is the manual if you want to look at the wiring etc.

https://www.parts4heating.com/v/vspfiles/images/pdfs/MiniMaxPlusPowerMaxIG.pdf

 

[Rocco]

I have the same heater and have worked on it every season. The good news is that the heater is designed that so in order for it to fire it must follow the same steps each time, with each light on the front representing a step. Here is what the service manual states.

The HEAT light is attached to the MV (Main Valve) terminal on the module. This terminal does not receive voltage until a Pilot Flame has been established. Once the MV terminal has voltage, it tells the Gas Valve to open and gas flows to the Burners and is ignited by the pilot flame.

Troubleshooting for: Power/T-Stat/Aux/Press/Service/No Spark:
1. Check the 3 lights on the back of the circuit board. These 3 lights are connected to 3 different controls in this order - #1 - High Limit. #2 - Thermal C/O. #3 - Pilot Valve

2. If the Pilot Valve light is Off, check the wiring from the circuit board to the module - Red wire should be attached to the MV terminal - White wire should be attached to the MV/PV terminal - Blue wire should be attached to the PV terminal and the Orange wires should be attached to the #6 Terminal. There will be 2 Ground wires attached to the Module. #4 Ground wire to the Gas Valve. #5 Ground wire to the cabinet.

3. If all wiring is correct and still no Pilot Valve light pull the Orange wire off of the #6 Terminal at the Module and test the wire for 24 VAC - if there is 24VAC, that means the board is O.K and the Module is defective. If you do not see 24VAC at the wire, the Board is defective.

4. If the Thermal C/O light is out - the Thermal C/O is defective.

5. If the High Limit Light is out - the High Limit is keeping the Heater off.

I do not recall where I was able to find the manual but I can email to you if you like.

 

[mjohnson003]

Thanks Rocco and Paul!

Thermostat/control board were replaced about 2 weeks ago. This problem existed before and after. (although by replacing the board I can now use both the Spa and Pump circuits)

All three LED's on the back of the control board are lit. So I think I am ok there. I also have 24 VAC on the wire you mentioned. When I cycle the heater on, with the door removed, I have no flame at the ignitor. As soon as I tap the panel to the right of the control board (where the ignition module it mounted on the backside), everything kicks on as normal. That is the only thing that seems to get it to come on.

I am really thinking it is likely the actual ignition module at this point? I've removed, cleaned and reconnected all wiring and connectors, and everything seems to have continuity ok. Is there anything mechanical in the ignition module that would respond to a light, sharp tap like that? Relays? Cold solder joint internally?

 

[ps0303]

Definitely sounds like the control/ignition module is an issue. I would suggest that you replace it and see what happens.

 

[mjohnson003]

It was the ignition module. I replaced it about two weeks ago, and it has worked great ever since

 

[ps0303]

Glad to hear all is good now.