Pentair MasterTemp 400 Burner won't light

[CANV22]

Dear TFP forum members,
I live in southern Nevada, as the 3rd homeowner, with an in-ground pool (~16.5K gal). The pool equipment includes a Pentair MasterTemp 400, natural gas heater. I'm not sure of the age of the heater but I would say likely 6 or 7 years old. A few days ago I started the heater but ultimately the burner does not come on at all and eventually shuts off with the Service Heater light on. I have begun to troubleshoot the issue and have removed the side and top panels of the heater to see the LEDS under the top cover panel and removed the metal cover of the Ignition Control Module box to expose the debug/ICM fault LEDs. the following are the details:

- When the heater is activated, the blower starts and runs while the Heater LED is blinking (calling for heat). After approx 10 to 20 seconds a "buzzing" noise emanates from the combi gas control valve and the burner never lights. The Fenwal ICM's LED is flashing 3 times repeatedly in succession for about 10 sec, and then stops flashing. After a few minutes, the heater shuts itself off. The burner never starts. There are no diagnostic/code LEDs lit from the heater LCD PCB under the top cover.

Troubleshooting steps I have taken:
- I don't own a Manometer so I have not verified the actual inches of water column readings of the incoming gas port or the out port. However, I did remove the cover and electromagnetic solenoid for the gas valve and manually lifted the "piston" and heard and smelled gas flowing (would assume into the combi gas valve unit).
- I checked that the 24VAC from the ICM was present on the terminals (gas valve switch in the ON position) of the gas valve relay(?) and electromagnetic solenoid after the ignitor should already be glowing red hot. When the gas valve switch is in the OFF position then the 24VAC is not ever present on terminals of the gas valve relay. So that tells me the switch is working properly and 24VAC is being applied to the electromagnetic solenoid to "pull" the gas valve piston up, and allow gas to flow into a chamber for ignition.
- I manually checked the resistance of the Ignitor (60 Ohms - good) and verified that it glows red hot when the ICM allows the 120VAC to energize the Ignitor. That tells me the Ignitor element is OK and the ICM to start an ignition cycle is working properly.
- From an older thread on this forum for a similar issue incl the "buzzing" gas valve relay(?), it was recommended to strike the gas valve unit with a hammer when the buzzing noise appears as an attempt to free a sticking relay(?). I tried this as well several times but the buzzing noise persists and no ignition of the burner.

So it seems to me that there is gas available to flow into the burner for ignition, but is not actually getting into the burner likely because the gas valve "piston" is not being "pulled" up by the electromagnetic solenoid. The buzzing noise is an obvious clue as to the source of the failure, but I don't know what is failing, and actually causing the buzzing noise.

I would appreciate any insight and guidance from the forum members to better understand where the failure is and what needs to be replaced to fix.

Thank you!

 

[ajw22]

Three flashes of the Fenwal LED indicates no flame being sensed.

Read Heater Flame Sensing - Further Reading

Post pics of the interior of your heater.

@swamprat69

 

[CANV22]

Hello ajw22,

Thank you for your quick response and the link to flame sensing. As far as I understand, an issue with flame sensing happens if the burner lit for a moment with perhaps a small puff of smoke and quick burst of heat from the exhaust. I don't get a momentary burner ignition. Could a flame sensing issue still be the cause of no momentary burner ignition? I could still improve the grounding between the bracket for the Ignitor and directly back to a ground on the ICM - per the Fenwal Technical Article (Improve Grounding in Gas Ignition Controls).

Also - if you could be a bit more specific on what pics you would like to see, then I won't take unnecessary pics.

 

[1poolman1]

Dear TFP forum members,
I live in southern Nevada, as the 3rd homeowner, with an in-ground pool (~16.5K gal). The pool equipment includes a Pentair MasterTemp 400, natural gas heater. I'm not sure of the age of the heater but I would say likely 6 or 7 years old. A few days ago I started the heater but ultimately the burner does not come on at all and eventually shuts off with the Service Heater light on. I have begun to troubleshoot the issue and have removed the side and top panels of the heater to see the LEDS under the top cover panel and removed the metal cover of the Ignition Control Module box to expose the debug/ICM fault LEDs. the following are the details:

- When the heater is activated, the blower starts and runs while the Heater LED is blinking (calling for heat). After approx 10 to 20 seconds a "buzzing" noise emanates from the combi gas control valve and the burner never lights. The Fenwal ICM's LED is flashing 3 times repeatedly in succession for about 10 sec, and then stops flashing. After a few minutes, the heater shuts itself off. The burner never starts. There are no diagnostic/code LEDs lit from the heater LCD PCB under the top cover.

Troubleshooting steps I have taken:
- I don't own a Manometer so I have not verified the actual inches of water column readings of the incoming gas port or the out port. However, I did remove the cover and electromagnetic solenoid for the gas valve and manually lifted the "piston" and heard and smelled gas flowing (would assume into the combi gas valve unit).
- I checked that the 24VAC from the ICM was present on the terminals (gas valve switch in the ON position) of the gas valve relay(?) and electromagnetic solenoid after the ignitor should already be glowing red hot. When the gas valve switch is in the OFF position then the 24VAC is not ever present on terminals of the gas valve relay. So that tells me the switch is working properly and 24VAC is being applied to the electromagnetic solenoid to "pull" the gas valve piston up, and allow gas to flow into a chamber for ignition.
- I manually checked the resistance of the Ignitor (60 Ohms - good) and verified that it glows red hot when the ICM allows the 120VAC to energize the Ignitor. That tells me the Ignitor element is OK and the ICM to start an ignition cycle is working properly.
- From an older thread on this forum for a similar issue incl the "buzzing" gas valve relay(?), it was recommended to strike the gas valve unit with a hammer when the buzzing noise appears as an attempt to free a sticking relay(?). I tried this as well several times but the buzzing noise persists and no ignition of the burner.

So it seems to me that there is gas available to flow into the burner for ignition, but is not actually getting into the burner likely because the gas valve "piston" is not being "pulled" up by the electromagnetic solenoid. The buzzing noise is an obvious clue as to the source of the failure, but I don't know what is failing, and actually causing the buzzing noise.

I would appreciate any insight and guidance from the forum members to better understand where the failure is and what needs to be replaced to fix.

Thank you!

If you opened any portion of the gas valve, it needs to be replaced. If it is buzzing, it needs to be replaced. Hitting a "stuck closed" gas valve can get it stuck in the open position and cause a runaway heater that you can't turn off. NEVER HIT the gas valve. What is the resistance of the igniter? It should be around 50 ohms.

 

[ajw22]

Hello ajw22,

Thank you for your quick response and the link to flame sensing. As far as I understand, an issue with flame sensing happens if the burner lit for a moment with perhaps a small puff of smoke and quick burst of heat from the exhaust. I don't get a momentary burner ignition. Could a flame sensing issue still be the cause of no momentary burner ignition? I could still improve the grounding between the bracket for the Ignitor and directly back to a ground on the ICM - per the Fenwal Technical Article (Improve Grounding in Gas Ignition Controls).

Also - if you could be a bit more specific on what pics you would like to see, then I won't take unnecessary pics.

It sounded to me like you were getting a momentary light. If you are sure you are getting no flame then don't worry about the flame sensing yet.

For the heater to light you need air, fuel, and spark. If the blower is running you probably have enough air. You say you checked the igniter although that is an inexpensive part to replace. So you are left with a gas problem.

You need a manometer to check your gas flow. And the manometer will tell you if the gas valve is opening because there will be a pressure drop when it opens.

Replace that gas valve at this point and get the right tools to diagnose a gas problem.

For pics I want to see the area with your gas valve and Fenwal and 120/20V plug. I also want to see the exterior gas line into the heater. And a pic of your gas meter showing the CFM of your gas service.

 

[CANV22]

Thank you 1poolman1 and ajw22,
The measured resistance of the ignitor is 60 Ohms. Which is right in the middle of the range (40 Ohms to 80 Ohms) Pentair says is good for the ignitor.
I have ordered a manometer and it will take a few days before it arrives and I can take measurements.
Do either of you know what causes the gas valve to buzz? My thoughts are that the ICM is not able to provide enough current to properly energize the solenoid. As I stated in my original post, I did measure 24VAC across the terminals of the solenoid on top of the gas valve, so from a voltage perspective it looks like the ICM is OK, but perhaps the current is not sufficient. Or perhaps the resistance of the coil of the solenoid is too high. As the coil looks to be just a solid wire, probably not a coil resistance isse, but easy to measure anyway.

 

[1poolman1]

Thank you 1poolman1 and ajw22,
The measured resistance of the ignitor is 60 Ohms. Which is right in the middle of the range (40 Ohms to 80 Ohms) Pentair says is good for the ignitor.
I have ordered a manometer and it will take a few days before it arrives and I can take measurements.
Do either of you know what causes the gas valve to buzz? My thoughts are that the ICM is not able to provide enough current to properly energize the solenoid. As I stated in my original post, I did measure 24VAC across the terminals of the solenoid on top of the gas valve, so from a voltage perspective it looks like the ICM is OK, but perhaps the current is not sufficient. Or perhaps the resistance of the coil of the solenoid is too high. As the coil looks to be just a solid wire, probably not a coil resistance isse, but easy to measure anyway.

24 volts at valve and it won't open (buzz), need new valve. You opened the valve, need new valve.

 

[swamprat69]

As 1poolman1 mentioned gas valves are not user serviceable. If you have disassembled the gas valve, it should be replaced. A gas valve solenoid that is buzzing can be caused by insufficient voltage ( weak transformer, dirty contacts in the circuit or frayed/loose wiring) , but you would notice a voltage drop at the gas valve under load. It can also be caused by a mechanical problem with the solenoid, but in that case you would notice that the amp draw of the gas valve would exceed the amp draw stated on the gas valve label. If you are trying to measure a very low amp draw with a clamp around ammeter, you can take multiple wire turns through the clamp and divide your reading by the number of turns through the center of the clamp to get an accurate reading.

 

[CANV22]

Thank you swamprat69 and 1poolman1 for your last feedback.
My manometer was delivered so I took measurements of the Inlet and Outlet pressure. My manometer does not directly measure in inches water column so I made my measurements in psi and converted to inches w.c. by using 1" w.c. = 0.03613 psi. I also remeasured the VAC (true RMS) across the gas valve solenoid terminals and measured using a clamp on amp meter the AC (true RMS) current in one of the solenoid wires. I took the VAC and Amp readings with the thought of ruling out a potentially bad Fenwal ICM driving the gas valve solenoid.
Please note that except where noted, all the gas Inlet/Outlet pressure, VAC and AC current measurements and values were taken when the gas valve was "buzzing".

Conditions for first reading (baseline system - in an all OFF state):
Heater OFF
External Main Gas Valve OFF
Gas Valve Switch OFF
Manometer connected to the Inlet Port
Measured pressure reading: 0.000 psi (as it should be).

Conditions for second readings
Heater ON
External Main Gas Valve ON
Gas Valve Switch ON, and "Buzzing"
Positive terminal of Manometer connected to the Inlet Port
Measured pressure reading: 0.275 psi = 7.61 inches w.c. (according to the Pentair Installation manual the Min Inlet pressure = 4" w.c.; Max Inlet pressure = 14" w.c. My measurement is above the min and approx 1.5 inches w.c. less than a center point of 9" w.c.). My conclusion is that 7.61" w.c. is sufficient to at least allow the Burner to start.
VAC (true RMS) across the solenoid terminals = 24VAC.
AC Current (true RMS) through one of the solenoid wires (clamp on meter) = 0.55 Amps (is that what you would expect?). When the buzzing stops the current is 0.00 Amps as expected.
Assuming 0.55 Amps (true RMS) through the solenoid is a Good value, then together with the 24VAC at the gas valve terminals I conclude that the Fenwal ICM is likely correctly driving the solenoid, and the issue of the burner not starting is the gas valve vibrating/buzzing, not allowing gas to flow through the Gas Valve Combi unit and mix with the air from the running Blower and be ignited by the red glowing Ignitor.

Just to complete the pressure measurements I connected the manometer to the Outlet Port and with the other conditions the same as the second reading I measured -0.143 psi = -3.96" w.c. Other than the fact that it is indeed a negative pressure, not sure the actual value has much meaning as we know that no gas is getting through the gas valve.

For good practice and maintenance I went ahead and cleaned the ground connections (one outside the control box and two inside the control box) and added a ground wire directly from the Ignitor metal bracket back to the Fenwal ICM ground, inside the control box following the Fenwal Technical Article (Improve Grounding in Gas Controls) recommendation.

I have attached various pics of the inside of the heater, control box, combi gas valve, added grounding wire from Ignitor bracket back to Fenwal ICM ground and the gas pressure readings on the Inlet and Outlet ports. I have also included a pic of the external gas pipeline to the heater. You will see that a Flex line is used although NOT recommend by Pentair. and the incorrect orientation of the "T" fitting for the sediment trap. Seems some plumbers do not know not to use Flex line and the correct orientation of the T fitting for a sediment trap. Even though the Flex line is NOT recommended and should be changed to a fixed pipe, I'm still getting sufficient gas pressure on the Inlet to at least have the Burner start. The Flex line may not allow enough gas flow after the burner starts, but it should at least be OK to get the burner to lite.

So unless someone thinks otherwise, I do agree with your earlier conclusion that the combi gas valve unit needs to be replaced and that should at least get the burner to lite.

Your feedback is welcome.

 

[Asherk74]

I’m having a similar issue; the biggest question is; has it ever worked?
If not, could be insufficient gas flow (I’m struggling with this now, as I’ve never got my $3500 heater I still to light as of yet)

 

[CANV22]

Hello Asherk74,
My heater was installed by the 2nd homeowner but I do believe it did work at one point. And the exhaust port does look like it had been working in the past.
Do you have a manometer to measure the Inlet pressure of the Combi Gas Valve unit?

 

[1poolman1]

That flex pipe will not let enough gas into the heater for it to function properly if at all. It should be hard piped all the way to the heater. Did one two weeks ago. Two other companies unloaded a parts canon but it wouldn't light. Replaced flex with pipe and fired immediately.

 

[Poolbreh]

James does a good job explaining the static and dynamic test here

Case study to determine root cause of Pentair mastertemp 400 not igniting

The history: -Last summer, we bought house and upgraded to new pool heater, Pentair Mastertemp 400 -after installation, we cannot get ignition; Pentair rep comes out, says not enough gas flow -Gas company comes out, upgrades meter to 400k btu (max), 'listens' to amount of gas flow at heater...

www.troublefreepool.com

 

[CANV22]

UPDATE: Using the feedback from swamprat69 and 1poolman1 and my analysis and diagnosis (followed the Pentair MasterTemp Pool & Spa Heater Installation & User's guide - Section 5 Troubleshooting) I decided that the most likely culprit preventing the Burner from igniting was a faulty combi gas valve unit so I ordered a new one. I also decided to replace the 3/4" flex tube (see pic below) with fixed 1" gas piping to a 1" x 1" x 3/4" T with correct orientation with a 1" sediment trap, followed by 3/4" piping and Union (enable service/maintenance) see pic below of the new gas line installation.

After installing the new combi gas valve unit with new gas line, I activated the Heater. After the Blower had run for about 20 sec, the burner correctly ignited! I also visually verified that the gas meter Half Foot dial was turning at a constant rate. The Heater continued to run without any error LEDs lit or error codes on the display. I now have my Heater up and running correctly.

I want to thank everyone for their helpful advice and guidance!