MiniMax NT Heater - No Ignition Sequence

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If you are doubtful of your meter skills, probably the easiest way to troubleshoot is to first confirm that the wire to GND on the ignition control and case/cabinet ground are the same by setting the meter to ohms and measuring from that wire to a metal part of the cabinet. The meter should read zero ohms. Put the wire back on GND. If you have confirmed that the Igniton control GND and case/cabinet ground are the same , you can then keep one meter lead attached to case/cabinet ground by loosening one screw on the ignition control mounting plate ( such as ther upper left screw of the mounting plate ) and inserting one meter lead between the mounting plate and the metal heater cabinet and tightening screw to hold meter lead in place. Then set the meter to AC volts. Measure volts to the TH wire on the ignition control with the lead that is not attached to the cabinet. If you do not get 24Vac, you should then measure the voltage at both contacts on the blower/fan air pressure switch. One contact should be labeled C or common and one contact should be labeled NO or normally open. If you do not have 24Vac on the contact labled NO, then the air pressure switch is not closing the normally open contacts or you do not have 24Vac at the C or Common on the air pressure switch even though the fan/blower is running and we can troubleshoot for that problem. If you do not have 24Vac at the C or common connection, then an upstream safety in the circuit is open and you can backtrack through the safety circuit to identify the open safety.
 
Ok, here's where I'm At:
-Disconnected GND wire. Put one multimeter lead in GND wire, and touched the cabinet with the other lead = 2.2 ohms.
-Reattached GND wire. Put lead behind top left ignition board mounting screw. Removed TH wire from ignition board. Tested TH at the terminal, and tested the wire = 0 VAC in either direction.
-Reattached TH wire to board.
-Tested C contact on blower = 0 VAC
-Tested NO contact at blower = 25.1 VAC when connected to the main circuit board.
-Blower was running at the time
 

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Your air pressure switch does not seem to be closing when the fan/blower/inducer is running. Your air pressure switch seems to have a yellow label ( part # 472182 ) which would have a set point of - 0.95"WC. Search results for: 'pentair air pressure switch' The usual causes for the switch not closing are switch failure, blockage of the tubing or connections, cracked tubing, dirt in the vanes of the blower wheel or inadequate blower RPM. Without a digital manometer to test the actual pressure being developed by the blower against the setpoint, you could try removing the tubing from the air pressure switch and blowing vigorously towards the blower assembly and reattaching. If that doesn't work, you would need to remove the cabinet parts to access the tubing and blower assembly. Pull and check the tubing for blockages/cracks. Clear the barbed tubing attachment at the blower housing with a toothpick or paperclip ( do not try clearing the barbed attachment at the pressure switch as you may damage/ruin the pressure switch diaphram ). Reattach everything and try to start heater again. If it still won't fire up, we can go on from that point.
 
-Pulled the hose off the pressure switch.
-Blew as hard ad a could as long as I could.
-Pulled hose off the blower.
-Bless as hard as I could as long as I could from either end.
-Cleaned blower out with a toothpick.
-Reattached hose to blower.
-Blew again as hard as I could as long as I could.
-Reattached to switch.
Nothing. Still E04.
 
You seem to be down to either the blower is not developing enough negative pressure to activate the pressure switch or the pressure switch is bad. You cannot be sure which it is without checking the pressure at the tube that attaches to the pressure switch with a digital manometer. To confirm it is one or the other you could "briefly" jumper the 2 wires attached to the NO and C contacts of the pressure switch to see if the heater will fire up. This would confirm that it is either one or the other, but not which one.
 
Made a Jumper out of white romex copper wire, unshielded on both ends.
Left the leads on the pressure switch.
Held one wire on the NO contact and tapped the other end on the C contact = no response.
Held it there a little longer = no response.
Blower was running at the time.
 
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Then you are down to either not developing enough enough pressure to close the air pressure switch contacts or the pressure switch is bad. You could get an inexpensive digital manometer from amazon since you would not be using it every day like a technician would. I tend to shy away from throwing parts at a unit without knowing exactly what the problem is. But that choice is up to you.
 
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Thanks for all your help on this. I found a switch on Amazon, so I'll be able to return it if it doesn't do the job. I'll let you know how it goes.
 
You know that the pressure switch was not closing because when you jumped it out you got the heater to run. If you installed a brand new pressure switch and it still won't close, it would seem to point to not enough pressure being developed to close the pressure switch. This could be confirmed with a digital manometer. You would also be able to tell with a digital manometer just how much short of the pressure needed to close the pressure switch it is at. If you are sure that the tubing is not blocked or cracked, I would look at problems that would cause insufficient flow i.e. weak blower motor capacitor, failing/worn blower motor bearings, buildup of dirt on the cupped vanes of the blower wheel or a blockage of flow through the heater (normally a blockage at the heat exchanger). You could take a reading of the blower motor amps while it is running against the listed running amps as a helpful indicator. Excessive amperage would indicate that the blower motor is trying to move adequate air but is being restricted for some reason (weak capacitor or worn/failing bearings). Lower than normal amperage would tend to indicate a restriction to airflow causing the blower to do less work than it is capable of ( blocked or partialy blocked heat exchanger or dirt buildup in the vanes of the blower wheel).
 
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Wow, sorry to hear about this. This is where heaters can be frustrating. I would also check the electrical connections on the switch and at the other ends. Also, make sure the air hose connections are good.
 
The results are in.
-.16 wc (using the hose that came with the manometer not the heater). It appears there isn't enough suction.
It doesn't sound like the fan is struggling at all, and there's a good amount of air being foced out of the unit.
I also started getting a LO error. Is that water pressure? Air pressure? Gas?
 

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setsailsoon said:
Wow, sorry to hear about this. This is where heaters can be frustrating. I would also check the electrical connections on the switch and at the other ends. Also, make sure the air hose connections are good.
Click to expand...
Thanks! I pulled the wires of all the connections, and they all seemed super tight.
 
Where are you getting your reading of -0.16"WC? You should be disconnecting the tubing from the heater pressure switch and attaching it to the manometer in order to observe the actual pressure that the pressure switch is seeing.
 
I tried that, but the hose diameter was too large for the manometer. I'll try again now to see what the switch is getting with the existing hose.
 

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