Pentair Mastertemp 400 won’t reignite

greentoblue

Member
Jan 3, 2025
8
keller tx
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Ok so I have a Mastertemp 400 just out of warranty the won’t reignite. At first it wouldn’t ignite at all and after a rundown of all the possibilities with my pool guy it came down to the gas control valve. I bought a used one on eBay and it ignited but wouldn’t reignite. Thinking I shouldn’t have gone cheap and bought used, I bought a new one off of Amazon and same issue. It ignigjted and got to 104 then it would maintain the temp or reignite. Service light is on and I am at a loss what could be the cause.
 
Welcome to TFP.

When the MasterTemp fails to light, does the blower run?

Is the heater connected to automation?

Which Service LED - Service System or Service Heater?

Have you looked at the diagnostic LEDs and the LED on the Fenwal box when the heater fails to light?

 
TY for your help!

The blower runs as it tries to kick on, makes a clicking sound at the valve. I replace the valve a second time and it ignites and works properly only once.

I believe it is connected to automation, service heater light, I can recheck the diagnostic leds but believe we have done that, I will recheck. My pool guy thinks it may be the gas pressure and he recommends a plumber with a manometer, only I can’t understand why it work fine one time and not a second.
 
Gas technician with manometer was going to be one of my suggestions.

You have to see what the gas pressure is when the heater fails to light.

Post pictures of your gas meter, labels on the meter, and heater showing gas pipe into it.
 
Here is the heater itself with a meter attached - and a pic of the meter
 

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Your gas meter is rated for 425 CFPM, which is marginal for a 400K heater. What other gas appliances do you have in the house?

What is that gauge on the end of your heater gas line?

Check the diagnostic LEDs and also the diagnostic LED on the FENWAL box.

You may also want to check the igniter.

 
It looks like the meter reads 12 psi and it doesn’t move as the gas valve tries to open. I am almost certain if I install a new gas valve it will work the first time but not a second.
 
You may have sediment in your gas that is clogging the gas valve.

A gas tech needs to open the gas line and clear the sediment trap, and purge the gas line.

You could have a malfunctioning gas meter or regulator. I had my house gas meter fail and needed the gas company to come out and replace it.
 
The meter was left behind after the gas line extension for the heater. We have a central gas heater, stove and tankless water heater all pulling from that meter.
 
The meter was left behind after the gas line extension for the heater. We have a central gas heater, stove and tankless water heater all pulling from that meter.

You should have a larger meter if those appliances kick on while running the pool heater.
 

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You should have a larger meter if those appliances kick on while running the pool heater.
Ok I will call the city and request a replacement meter that is also larger. After that I will work to clear out any sentiment. Does the 12 psi on that meter seem right, is a manometer measurement different? Could it be sediment ruining the gas valve after the first run and would that mean I may need a third replacement meter after the “to does” above are done?
 
There is no way that it is 12 psi.

Can you show the whole gas line, manometer and how you are testing?
This meter was left behind after a 3/4 line was installed 3 yrs ago to cover the larger gas pull. It seems I may need a bigger meter as well. All of the electric seems fine but the two replacement valves only work a single time then just make a clicking sound as it tried to reopen a second time. When I replaced the gas valve twice I didn’t blow out or address any potential debris in the line but there is a trap of sorts you can see in the pic
 

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1.2 psi is 33.2 in WC (inches of water column (conventional)) and you cannot put that much pressure into the gas valve.

That pressure will damage the gas valve and make it malfunction.

The pressure needs to be between 4" w.c and 14" w.c.

If you use higher pressure (Typically 2psi) from the meter to the heater, you need a regulator near the heater to decrease the pressure from 2 psi to about 7" w.c at the heater.

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How long is the gas line?

3/4" pipe is ok to about 150 feet for a 2 psi gas pressure, but you need a regulator near the heater to decrease the pressure to heater inlet range.

The gas going to your other household appliances will also need to be low pressure and the appliances require a regulator to make sure that the pressure is correct.

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Ok I think you have it figured out - it’s about 35 feet long from the meter to this pic and there is no regulator currently near the heater- perhaps with a regulator adjusted properly one of these three will work or a new one with work and reignite a 2nd time
 

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