Pentair MiniMax NT heater w/DDTC does not ignite

Eric_yang

Well-known member
Jun 6, 2016
54
San Jose
There's an error LED flashes which indicates an air pressure issue. The blower fan keeps running at the low speed when the system is on, which is pretty strange. For a normal system, at the start up the blower fan should run at at full speed for 15s (pre-purge period), then slow down to half the speed to allow trial ignition for 7s (heating up process). After the flame is detected, the blower fan comes back to the full speed until the heating process is done.

I shorted the air switch outputs to deceive the DDTC that the air pressure was right. Then I heard several clicks inside the DDTC which I guess to change the blower fan speed or for ignition. But there's no ignition happened.

At this moment, I'm not sure if it's the DDTC does not provide the right signal or power for the blower fan to run pre-purge (full speed), or the blower is broken and can only run at the half-speed. The input DDTC seems right as I can measure a 24V presented at the TH pin.

I also changed the running cap of the blower. No luck.

Any suggestion, please?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
21,299
Laughlin, NV
Let's see if any of heater folks just missed your post. I am no help with your technical questions.
 

danpik

TFP Guide
Jun 4, 2012
1,720
western NY
some of these systems look for an open switch on the vacuum switch prior to start to verify that it is not jumpered and then when the switch closes allows the system to start. Have you verified that the igniter is getting power? should be 120 volts on a 120 system and 240 on a 240 system. Check and see what the resistance is on the igniter. should be 40-100 ohms.

Dan
 

Eric_yang

Well-known member
Jun 6, 2016
54
San Jose
some of these systems look for an open switch on the vacuum switch prior to start to verify that it is not jumpered and then when the switch closes allows the system to start. Have you verified that the igniter is getting power? should be 120 volts on a 120 system and 240 on a 240 system. Check and see what the resistance is on the igniter. should be 40-100 ohms.

Dan
Hi Dan,

Thanks for the reply.

The igniter is measured 123Ω. I measure no 240V or 120V on the igniter. Is it true that the igniter should fire when a 240V is presented?

My feeling is that it is either the blower or the blower control, which is inside the DDTC, is gone bad. In the past, the fan was running at very high speed immediately right after the heater was turned on, in order to blow out all the dirty stuff from the grill. But now, the blower fan is keeping in low speed. My DDTC also blinking the red light which suggests air flow issue.

I'm wondering how the blower speed is controlled, by halving the supply voltage or there's a control signal. From there I can further inspect if it's the DDTC problem or blower's problem.

P.S. As what you said I probably won't be able to deceive the DDTC by jumping over the air switch if the unit is checking an open-close-open sequence.
 

danpik

TFP Guide
Jun 4, 2012
1,720
western NY
If the system is working , the output wire to the igniter will have voltage on it. I wouldn't condemn the igniter at 123 ohms yet. If the error light is showing an air flow problem, then the vacuum switch is either bad or the system is clogged up somewhere.




the fan was running at very high speed immediately right after the heater was turned on, in order to blow out all the dirty stuff from the grill.
This is not what this is for. The purpose of the fan is to vent exhaust gas from the burner chamber. If there is "dirty stuff" coming out of the exhaust then the unit needs to be opened up and cleaned. The vacuum switch in these systems is to prove that the fan is able to pull air/exhaust thru the system and vent it out the exhaust pipe properly. As for the fan having two speeds, this is simple. There are two sets of windings in the motor, high speed and low speed. There is a temperature switch on the blower housing that monitors the temperature of the exhaust gas and sets the fan speed accordingly.

Dan
 

Eric_yang

Well-known member
Jun 6, 2016
54
San Jose
If the system is working , the output wire to the igniter will have voltage on it. I wouldn't condemn the igniter at 123 ohms yet. If the error light is showing an air flow problem, then the vacuum switch is either bad or the system is clogged up somewhere.





This is not what this is for. The purpose of the fan is to vent exhaust gas from the burner chamber. If there is "dirty stuff" coming out of the exhaust then the unit needs to be opened up and cleaned. The vacuum switch in these systems is to prove that the fan is able to pull air/exhaust thru the system and vent it out the exhaust pipe properly. As for the fan having two speeds, this is simple. There are two sets of windings in the motor, high speed and low speed. There is a temperature switch on the blower housing that monitors the temperature of the exhaust gas and sets the fan speed accordingly.

Dan

Makes sense Dan!

Is there a way to check the vacuums pressure switch is good?

I turned the heater on, measured the output pins of the vacuum air switch ,which was kept open; meanwhile, the blower was kept at lower speed and I could feel air pressure at the exhaust, but definitely not as strong as in the normal heating. I checked there was 240V supplied to the blower as well. Then I took the air switch out and blowed air into the hose, it was still kept open. Can I say the switch is bad?

I tried to open the blower motor but failed. The blower motor seemed tightly attached to the exhaust with all seams either caulked or insulated. I'm not confident to open it and check if anything clogged inside.

My plan is to replace a new air switch. If it does not work I'll call a technician to service the blower.