Mastertemp 400 heater issues

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Farmoci

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Jul 16, 2015
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Hello -

I am having Problems with my Pentair Mastertemp 400 heater. It won’t heat. It is doing exactly like the heater is this YouTube video.


It starts up. Heater LED blinks. The display shows the current water temp and shows the flame 🔥 icon. The fan works and air starts moving through the exhaust. I can begin to smell a little natural gas in the exhaust fumes. It goes through a series of clicks (click - a minute or so passes, another click - a minute or so passes, another click) and then the “Service Heater” light turns on.

I went through the troubleshooting guide in the manual. I changed the HSI Igniter and that didn’t fix the problem. I then changed the Ignition Control Module with no success.
I am already about $300 into this “repair” and the earliest I can get someone out to look at it is 2 weeks. I am assuming the gas pressure is ok as there is a gas grill on the same line that works (plus I can smell gas in the exhaust).

I typically use my Pentair ScreenLogic to control everything. Curiously, when I press the “Pool on” or “Spa on” buttons on the unit itself they don’t respond. I followed one of the previous threads that linked a video assessing the Membrane pad, and when I short the two pins closest to the yellow button on the control board nothing happens. If I try to turn it on from my ScreenLogic App, it does as above. Do I need to replace the control board???

I am at a loss. Any suggestions? Buy a new heater LOL?
 

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Check the voltage going to the ignitor on call for heat.

On a call for heat, the blower and HSI (Hot Surface Ignitor) are energized.

The HSI should receive 120 volts when you hear the blower start.

If the main supply voltage going to the heater is 120 volts, then the voltage reading to the HSI should be a clean 120 volts.

If the power to the heater is 240 volts, the voltage sent to the HSI is an intermittent pulse that "simulates" 120 volts.

The intermittent pulse will not read as a clean voltage by a multimeter.

A true RMS will get a better read on the voltage, but the voltage might read higher or lower than exactly 120 volts.

In about 20 seconds, the gas valve opens and ignition should occur.

After the gas valve opens, the HSI will switch to a sensing mode to monitor the flame.

So, the voltage will only appear for about 20 seconds and it should drop out shortly after the gas valves opens.

When the HSI switches to flame sensing mode, it is looking for a microamp current in the 1 to 10 microamp range (1.0 to 10 µA).

If the flame sensor does not read at least 1.0 microamps, the Fenwal controller will shut down power to the gas valve.

Is your heater connected to 120 or 240 volts?

Can you show a picture of inside the metal box like below?


Mastertemp Fenwal.jpeg
 
Last edited:
Check the gas pressure at the inlet static and on call for heat.

The pressure static should be about 7 to 10" w.c and it should drop only about 1 or 2 " w.c on call for heat.

Below, you can see that the initial pressure is good, but the pressure drops to zero on call for heat which indicates a gas supply issue.


Verify that all gas valves are open.

Verify that the gas valve in the heater is set to On.
 
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JamesW said:
Check the voltage going to the ignitor on call for heat.

On a call for heat, the blower and HSI (Hot Surface Ignitor) are energized.

The HSI receives 120 volts.

If the voltage going to the heater is 120 volts, then the voltage reading to the HSI should be 120 volts.

If the power to the heater is 240 volts, the voltage sent to the HSI is an intermittent pulse that simulates 120 volts.

The intermittent pulse will not read as a clean voltage by a multimeter.

A true RMS will get a better read on the voltage, but the voltage might read higher or lower than exactly 120 volts.

In about 20 seconds, the gas valve opens and ignition should occur.

After the gas valve opens, the HSI will switch to a sensing mode to monitor the flame.

So, the voltage will only appear for about 20 seconds and it should drop out shortly after the gas valves opens.

When the HSI switches to flame sensing mode, it is looking for a microamp current in the 1 to 10 microamp range (1.0 to 10 µA).

If the flame sensor does not read at least 1.0 microamps, the Fenwal controller will shut down power to the gas valve.

Is your heater connected to 120 or 240 volts?

Can you show a picture of inside the metal box like below?


View attachment 335912
Click to expand...

Attached is the picture that I took before I changed out the Ignition Control Module.

How (or where) would I check the voltage to the igniter?

Check the voltage going to the ignitor on call for heat.
JamesW said:
Check the voltage going to the ignitor on call for heat.

On a call for heat, the blower and HSI (Hot Surface Ignitor) are energized.

The HSI should receive 120 volts when you hear the blower start.

If the main supply voltage going to the heater is 120 volts, then the voltage reading to the HSI should be a clean 120 volts.

If the power to the heater is 240 volts, the voltage sent to the HSI is an intermittent pulse that "simulates" 120 volts.

The intermittent pulse will not read as a clean voltage by a multimeter.

A true RMS will get a better read on the voltage, but the voltage might read higher or lower than exactly 120 volts.

In about 20 seconds, the gas valve opens and ignition should occur.

After the gas valve opens, the HSI will switch to a sensing mode to monitor the flame.

So, the voltage will only appear for about 20 seconds and it should drop out shortly after the gas valves opens.

When the HSI switches to flame sensing mode, it is looking for a microamp current in the 1 to 10 microamp range (1.0 to 10 µA).

If the flame sensor does not read at least 1.0 microamps, the Fenwal controller will shut down power to the gas valve.

Is your heater connected to 120 or 240 volts?

Can you show a picture of inside the metal box like below?


View attachment 335912
Click to expand...
 

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  • 022E8B18-944B-4A95-A7A0-F956A87C9587.jpeg
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    379.7 KB · Views: 113
JamesW said:
Check the gas pressure at the inlet static and on call for heat.

The pressure static should be about 7 to 10" w.c and it should drop only about 1 or 2 " w.c on call for heat.

Below, you can see that the initial pressure is good, but the pressure drops to zero on call for heat which indicates a gas supply issue.


Verify that all gas valves are open.

Verify that the gas valve in the heater is set to On.
Click to expand...
Thank you for your reply. Is there a poor man’s test for assessing that LOL. I don’t have a digital manometer to check the pressure. My gas line to the heater has a split to my grill. FWIW I did manually adjust the gas regulator to see if the gas grill flames became more intense and it seemed to. It didn’t make any difference for the heater however. I returned the gas regulator back to its original setting.
 
Testing from L1 to L2 should show 120 volts before call for heat.

On call for heat, testing from S1 to S2 should show a clean 120 volts for 20 seconds until the gas valve opens.

The 120 should be a clean 120 volts since it looks like your unit is wired for 120 volts power input supply.

022e8b18-944b-4a95-a7a0-f956a87c9587-jpeg.335916
 
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Farmoci said:
Is there a poor man’s test for assessing that LOL. I don’t have a digital manometer to check the pressure.
Click to expand...

Gas Pressure Test Kit, 0 to 35 In WC Model # 78060

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Gas Pressure Test Kit Set Manifold with Ease

Our gas pressure test kit is easier to use than a manometer. This compact kit helps you accurately set manifold pressure for natural or L.P. gas.
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Hti-Xintai Digital Manometer, Dual Port Air Pressure Meter Pressure Gauge HVAC Gas Tester, Large LCD Display with Backlight, Basic: Amazon.com: Industrial & Scientific

Hti-Xintai Digital Manometer, Dual Port Air Pressure Meter Pressure Gauge HVAC Gas Tester, Large LCD Display with Backlight, Basic: Amazon.com: Industrial & Scientific
www.amazon.com
 
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If you have a clamp ammeter, you can check for amperage on the wires going to the ignitor.

The amperage should begin at the same time as the blower starts, or shortly after, and it should continue for about 20 seconds until just after the gas valve opens.
 

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Just a follow up to post the resolution to my heater problem. First, I’d like to thank everyone for their input. It really makes this forum valuable and quite informative.

It turns out the heater was fine. My gas line regulator valve failed. Apparently, it was not installed properly (it is supposed to be installed upside down when it is outside exposed to the elements - less likely for water damage supposedly??). Anyhow, I called the gas company to assess the pressure in the line and the technician noted the incorrect valve installation. He changed out the regulator valve and now everything runs perfectly. I guess if I had the manometer to check the pressure like it was suggested above, I would have seen the pressure drop.

Anyhow, thanks for everyone’s suggestions. Maybe this will help someone with a similar problem in the future.
 
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Not all gas regulators can be installed upside down. Refer to the installation instructions. Most times the vent is threaded so that you can install a compression fitting and a piece of tubing in a U shape so that water does not enter the vent.
 
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