Heater Won't Fire

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K

Kit

Bronze Supporter
Mar 10, 2016
325
Medford, Oregon
Several days ago I discovered that my Pentair MasterTemp 400 heater shut off before reaching the set temperature. This was the case in both the general filtration mode & the spa mode. Having had this issue before, I discovered that the thermal regulator was corroded & would not open. So I installed a new regulator. Unfortunately, it did not solve the problem. There was no error code on the LCD screen & the Service Heater light was NOT illuminated. Looking at the rear of the circuit board, none of the LEDs were lit (except LED9 was dimly lit a green color).

Next I tested the thermistor by removing the 2 wires & connecting a resistor between them. The heater still would not fire. Finally I cleaned all of the electrical contacts. I even removed the circuit board (which had bit of corrosion) & gently cleaned it with electrical contact cleaner & a soft brush. After I reconnected everything, still the heater would not fire. However, the Service Heater light was on; but no error code. On the back of the circuit board, LED11 was lit (which I assume is associated with the Service Heater light).



So, at this point I am at a loss what to do next. With no LEDs illuminated, I'm starting to get suspicious that the circuit board itself might need to be replaced.
If anyone can offer me some guidance, I would truly appreciate it. Thank you so much.

Kit
 
If the bypass valve is broken the heater will short cycle and make noise. If you look in the hole where the thermal regulator goes, you should be able to see the black disk. If you look in the water inlet, you should be able to see the spring.

You will have to take the manifold off to replace the Internal by-pass kit P/N 77707-0001.

Guide to replacing the bypass valve is for the residential MasterTemp model.

The ASME commercial MasterTemp model has a different manifold with a 2-inch Pipe Plug, (for access to Internal BypassValve), located at the top of the Manifold.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com www.troublefreepool.com
 
When I replaced the thermal regulator, I looked into the hole & it appeared that the bypass valve was in place. I will confirm this again more carefully.

Since the heater blower will run for about 30 seconds but the heater doesn't fire, it seems like the igniter could be faulty. I will check to see if there is any obvious problem there.
 
Look at the Fenwal box and see if its LED is blinking when the heater shuts down.
 
I opened the Fenwal box (see below) & all connections looked clean & secure. I tested the fuse & it was fine. However, while the blower was running, the light in the box blinked a sequence of 3 several times. I thought that I had read on this forum that it might be an indication of a bad igniter. Your thoughts? Thank you.
 

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Thank you for the links. I did test the resistance across the flame sensor. It showed 95 ohms. I don't know if this is a problem since the article indicated an ideal reading of 50 ohms. If need be, I can probably remove & inspect the flame sensor if necessary. However, testing the flame sense circuit might be a stretching my electrical testing knowledge.
 
From what I gather, the ohms should be 40-80 ohms at room temperature. The 95 ohm reading I got was at ambient temperature of about 45F. I don't know if that would make a difference. And if so, would the cooler temps cause the ohm reading to decrease or increase? i just hate to end up replacing the igniter unnecessarily.

Also, I might add that when the blower was running I did NOT smell any gas.
 

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Well you can check the gas pressure with a manometer.

You should observe if you hear the click of the gas valve opening when the heater tries to start.

Is your heater NG or propane?
 
If the blower is not starting you are not getting far into the start sequence.

The Wiki explains how to diagnose a blower problem using a multimeter.
 
The flame igniter in my Pentair MasterTemp 400 heater has an ohm reading of 95 ohms. According to Pentair tech support, the acceptable range is 40-75 ohms at room temperature. My question is this: Since the 95 ohm reading was taken when the air temperature was about 45F, at room temperature would the 95 ohm reading be higher or lower? Just curious. I can always remove the igniter & check the reading at room temperature. Thank you.
 
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