Pentair 400 Heater not igniting, no errors, everything visually working

[BillT2]

Hi guys, I've spent a good amount of time troubleshooting this myself and am out of ideas.

Heater has been working fine for months with no problems. I realized it was not heating one day and it has not ignited at all since then. It goes through the ignition process, everything appears to be working, but there is no ignition when the system clicks - it tries several times and then the service heater light comes on. There are no error LED's at any point other than when they all flash on when the unit is started. The red LED inside the unit flashes 3 times for Ignition Lockout after the unit tries to start. The blower appears to have strong suction in the intake and blowing from the exhaust, I checked inside the exhaust with a pipe camera and the drum looks completely clean/dry, blower looks clean with the camera too, no staining anywhere etc, there is no corrosion inside the unit or near grounds etc that I see. At most the unit is 10 years old, inside is very clean.

I've gone through the troubleshooting process in the manual, which ends up at 2 options: "replace HSI igniter" and "Replace Ignition Control Module" - I tested the old igniter resistance and it seemed to be fine but I had a new one and swapped it, new igniter is also working fine - both were too hot to touch when removing. I tested the leads to the igniter while the system was trying to start, and the voltage I got matched what is supposed to be output, per the manual - a pulsing range under 240v. Lots of gas flowing (unit is right next to the meter) and I smell gas each time the unit tries to start. Spa jets appear to have the same water flow as always and other pool equipment seems to be fine.

So I could try to get someone to diagnose, but that can be a Crud shoot too. Any suggestions? Thanks for reading
edit - the next step I was thinking of is to replace the Ignition Control Module, as that is what is suggested in the manual - but it's not cheap and it appears to be functioning, at least in the ways that can be tested per the manual

edit: Solution was replacing the gas pressure regulator between the gas meter and the unit, which had gone bad - everything else was working normally.

 

[JamesW]

I tested the leads to the igniter while the system was trying to start, and the voltage I got matched what is supposed to be output, per the manual - a pulsing range under 240v.

Measure the current with a clamp ammeter.

Lots of gas flowing (unit is right next to the meter) and I smell gas each time the unit tries to start.

Measure the gas pressure to see if it is good before start and during call for heat.

If you have gas and a hot ignitor, there should be ignition.

Check the flame current.

Remove one of the lower manifold bolts to see if water comes out.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

Heater Flame Sensing - Further Reading

www.troublefreepool.com

 

[JamesW]

 

[BillT2]

Thanks for the response James - there are some things I haven't tried on that first link that I'll work on. The second link I had actually seen but I believe only applies if the flame is igniting briefly and mine is not igniting at all. I'll have to buy or borrow a clamp meter.

Is removing the manifold bolt to check for water in the drum? I checked the drum with a camera so just verifying what I'm looking for

I had seen gas pressure mentioned in the manual, but where should I check it and is there a certain expected PSI? I have a gauge in-line from the meter to the heater, but it's not functioning. I have a replacement i can swap in, but is that useful? Or am I supposed to be checking somewhere inside the unit or something?

 

[JamesW]

Is removing the manifold bolt to check for water in the drum?

Yes.

had seen gas pressure mentioned in the manual, but where should I check it and is there a certain expected PSI?

 

[JamesW]

The inlet pressure should be between 4 and 14 inches of water column.

The pressure will drop as the heater tries to light, but the drop should not be more than 2" w.c and the pressure should not drop below 4" w,c.

Only check the inlet pressure and do not worry about the manifold pressure.

 

[BillT2]

Thanks a ton for the links - I must have missed that table in the manual. I am going to go pick up a clamp meter, and I can probably hook my gas gauge up on the unit - I'll update after trying a few things

 

[JamesW]

The manifold pressure is actually negative and you will probably not need to test the manifold pressure.

 

[BillT2]

I'll post a video of the unit starting up below. I don't know if what is happening is expected behavior or not.

I checked the igniter wires with the clamp meter, which are getting about 4 amps, and then as soon as something clicks (maybe the gas valve opening, I could smell gas at that moment each time) the power to the igniter is cut, and then returns about 12 seconds later - this happens during each attempt. I don't know if the igniter is supposed to still have power when the gas valve opens, and don't see anything on this in the manual or other links unless I've missed it. Anyone know?

The manual says the igniter goes into sensing mode 'after ignition' but it's not specified if the igniter should be on while gas is flowing, but has not yet lit - on my unit the igniter appears to lose power as soon as the gas valve opens.

 

[JamesW]

The blower starts first, which should close the air flow switch.

Once the Air Flow Switch closes, the TH terminal get 24 VAC to activate the HSI (Hot Surface Ignitor).

After 20 seconds, the VAL (Gas Valve) terminal gets 24 VAC to power the gas valve.

The ignition should happen within about one or two seconds.

So, the ignitor will switch off about a second or two after the gas valve is supposed to open.

The ignitor seems to be working correctly, so that points to the gas valve or gas pressure.

Make sure that the valves are all open and check the gas pressure.

 

[JamesW]

The ignitor should still be hot enough that it can turn off as soon as the gas valve gets power and the gas should still ignite.

So, I suspect that it is a gas supply issue.

If you smell gas, that indicates that the valve is probably opening and letting some gas come out but the pressure is probably dropping off fast as shown in the video that I linked to earlier.

The inlet gas pressure was fine until the gas valve opened and then it went to zero.

 

[JamesW]

You can check for 24 volts AC at the gas valve when it is supposed to open.

Make sure that the On/Off switch on the valve is in the On position.

Check the gas shutoff valve right outside the heater to make sure that it is open.

Check for a gas shutoff valve near the meter.

Check the inlet gas pressure before the gas valve opens and after it opens.

 

[JamesW]

It sounds like the gas valve is clicking open and closed.

In my opinion, the most likely issue is a gas supply issue external to the heater.

The pressure test should tell us where to go next.

This is natural gas and not propane, correct?

Check all external valves on the gas supply line.

 

[wireform]

Is there any chance a part of the gas line is below grade and took in some water diminishing gas flow.

 

[swamprat69]

The ignitor should be powered for a specified time after the gas valve is powered. This is usually printed on the fenwal label as either "ignition" or "trial for ignition" or "ignition time" and is usually less than 10 seconds.

 

[JamesW]

 

[BillT2]

Wanted to post an update to this - in short, the gas regulator had failed, and replacing it solved the problem.

I had tested most or all of the items mentioned in this thread, and after testing the gas line the unit suddenly started working again. I think the gas regulator got shaken loose briefly, and then the unit stopped igniting again. I replaced the regulator and have had no problems since. I think the old regulator had gotten stuck closed or partway open, where it was venting the gas out of the relief rather than going to the unit.