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Thread: Pentair mastertemp 400 cycling due to low gas flow?

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    Pentair mastertemp 400 cycling due to low gas flow?

    Had mastertemp 400 heater installed about 2 years ago pool guy that did the install says this issue with it cycling is because I don't have enough gas flow to the heater. Is there a definitive way to confirm this before I spend about $3000 replacing the gas line?

    The cycling seems to be worse when cold that is about 70-80 degrees, some days it runs for 10 minutes before the burner shuts off for 30-45 sec, but other days it only runs for 2-3 min then cycles. Is there an indicator light on the heater that confirms low gas flow?

    The run to the heater is 70ft with 1 1/4 in ground pipe. I talked to one plumber so far he said that it should be 1 1/2 for a 400k btu heater. My house is 30 years old so he also says pipe could be rusted or have moisture in it restricting the flow, in addition to it technically being too small.

    Sound like a correct diagnosis?


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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Sorry I don't know Bob, but we have a couple of guys here that are really good with heaters. I wanted to say welcome to the forum however, and I hope you enjoy your stay.
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    You've had the unit for 2 years and up till now it has run just fine?

    Does the Service Heater light come on when the unit stops?

    No indicator light for the gas supply.

    1 1/2 line is the usual size needed but there are some other factors and things that could cause this. Pentair is very specific on what size supply line they need to feed one of their units.
    Paul
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Bob I had same problem with my heater-about 200 foot run on 1 1/4" line and was not a dedicated line (which some said it should be) as line went to pool house then from there to pool pad behind pool house (it was existing pool went with larger heater when we moved in). I was sick at the thought of digging up beautiful mature landscaping for a bigger gas line and the expense (heater started but wouldn't ignite due to low flow). Easy fix was bigger gas meter (free fr gas company and they increased line size fr road too) and a plumber put in regulator for HIGH PRESSURE line and problem solved!!!! Gas for heater is about flow not pressure u should first measure your flow at heater
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    His problem might be more about location. Since he has So Cal Gas Company for his gas supply, they might not put a 2 psi line for a residential installation. I know when I built my pool, they put in a huge meter, but I was still limited to 6 -14" w.c. for my pressure. That means, he might need to up size the line for a 70 ft run that can support 400K btu's.
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by Killer95Stang View Post
    His problem might be more about location. Since he has So Cal Gas Company for his gas supply, they might not put a 2 psi line for a residential installation. I know when I built my pool, they put in a huge meter, but I was still limited to 6 -14" w.c. for my pressure. That means, he might need to up size the line for a 70 ft run that can support 400K btu's.
    I should have mentioned this too, I did already have gas company come out and install a larger meter. So I now have a huge meter too. I also tried running every gas appliance in my home at same time as pool heater. 2 furnaces, tankless water heater, range that meter was really spinning made no difference in the heater cycling.

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    The 1-1/4" should be good for up to 100' total equivalent pipe length for natural gas. Total equivalent pipe length is total straight pipe plus 3 feet per elbow. This assumes hard pipe, not flex.

    If there is anything else on the line, the line has to be sized for the total load.

    The meter should be a least 400 cubic feet per hour for the heater plus anything else that might run at the same time.

    The inlet pressure to the gas valve should be between 4" wc and 14" wc. When operating, the inlet pressure should not drop by more than 2" wc nor to less than 4" wc.

    The cycling is not likely related to gas supply.

    Is "Service Heater" on?

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by ps0303 View Post
    You've had the unit for 2 years and up till now it has run just fine?

    Does the Service Heater light come on when the unit stops?

    No indicator light for the gas supply.

    1 1/2 line is the usual size needed but there are some other factors and things that could cause this. Pentair is very specific on what size supply line they need to feed one of their units.
    Yeah its been doing this ever since installed new, since we don't heat the pool and rarely use the spa, I have just been dealing with it and getting by. With a solar cover on the pool it gets to about 90 degrees by june. It seams to be worse in the winter though last week kids used the spa it took hours to heat up. I am out of town this weekend I'll look at the light and confirm, but if I recall correctly the led on the display blinks when the burner is not firing. The blower keeps running the entire time it's the burner that cycles. Never a problem with the burner starting right up when heater turns on. When it is running we also notice the burned gas has a strong smell

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Sta rite pool heater problems

    See the above thread. The starite is essentially the same heater except for the outside.

    It also could be a flow issue. Can you post a picture of the system?

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Those things are real sensitive to air fuel mix, if it is not right, it wont fire to begin with, period. But air fuel mix is different than gas pressure or volume. Mixing/blending is done at the heater, pressure is the service applied to the heater. You can put a manometer in it and find out immediately if your getting enough gas.

    Since it is Saturday, im not working, and for better or worse, i don't commit pipe size and run length to memory, but i think You have up to 90' with 1 1/4 pipe. Don't hold me to that though.

    You could also check the thermostatic bypass, but if it has done this from day one, why didn't you just get factory service for it?
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by bobca1 View Post
    Yeah its been doing this ever since installed new, since we don't heat the pool and rarely use the spa, I have just been dealing with it and getting by. With a solar cover on the pool it gets to about 90 degrees by june. It seams to be worse in the winter though last week kids used the spa it took hours to heat up. I am out of town this weekend I'll look at the light and confirm, but if I recall correctly the led on the display blinks when the burner is not firing. The blower keeps running the entire time it's the burner that cycles. Never a problem with the burner starting right up when heater turns on. When it is running we also notice the burned gas has a strong smell
    WOW, since day one and you lived with it?

    Cycling on and off like that could also be something else other than gas flow.

    When you get a chance, we need to know that when it cycles, does the service hater light come on. If it does, if you remove the top you can flip it over and look at the board to see which LED is on. You will need to remove the front and back panels and then up under the top in each corner is a wing nut. Remove all four and then the top will come off.
    Paul
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    It's a flow issue and 1 1/4" is fine if they install regulators and create a high pressure line
    30,000 gallon gunite swg, 3HP VSP, Pentair TA-100D, 8' spa w table/water feature, waterfall and PCC 2000 infloor

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by Pool Clown View Post
    Those things are real sensitive to air fuel mix, if it is not right, it wont fire to begin with, period. But air fuel mix is different that gas pressure or volume. Mixing/blending is done at the heater, pressure is the service applied to the heater. You can put a manometer in it and find out immediately if your getting enough gas.

    Since it is Saturday, im not working, and for better or worse, i don't commit pipe size and run length to memory, but i think You have up to 90' with 1 1/4 pipe. Don't hold me to that though.

    You could also check the thermostatic bypass, but if it has done this from day one, why didn't you just get factory service for it?
    A manometer... cool that's exactly what I was thinking there must be a way to test the pressure at the heater while it's running. I had 2 plumbers come to my house so far I asked just that if there was a way to test but neither one knew how to do this. Is this something I can buy somewhere like amazon and connect myself to test?

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by ps0303 View Post
    WOW, since day one and you lived with it?

    Cycling on and off like that could also be something else other than gas flow.

    When you get a chance, we need to know that when it cycles, does the service hater light come on. If it does, if you remove the top you can flip it over and look at the board to see which LED is on. You will need to remove the front and back panels and then up under the top in each corner is a wing nut. Remove all four and then the top will come off.
    It really doesn't bother us much since we hardly use it, and in the summer it still heats spa ok. I'll check the lights in couple days when I get back home. Thank you all for the suggestions and advice!

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by JamesW View Post
    Sta rite pool heater problems

    See the above thread. The starite is essentially the same heater except for the outside.

    It also could be a flow issue. Can you post a picture of the system?
    Sure I'll post when I get back home...

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Quote Originally Posted by will View Post
    It's a flow issue and 1 1/4" is fine if they install regulators and create a high pressure line
    What is this exactly, a high pressure line? Does this mean put a regular at the end of run by the heater? Right now I have one regulator installed before the meter.

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Google how to make a manometer. Simple tubing on a board. Water height differential in inches is the pressure. Plus you'll need a 1/8" threaded to barbed fitting to go into the test hole.

    You can buy a manometer if you want.

    Natural gas can be run two stage with a 2 psi first stage from the meter to a regulator near the heater that steps down to the inlet pressure of the heater. This allows for smaller line for most of the run.

    Note: Consult with a qualified gas contractor for anything you're not sure about. Don't do anything that you're not sure that you can do safely.

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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Hey bobca1! This is a long shot but it sounds like the technician installed a propane heater when you have natural gas. A propane Mastertemp has a smaller Gas orifice so that would cause not enough gas flow, and would cause short cycling. It's rare and throws a lot of technicians for a loop. If you installer is a Pentair dealer then you should have a 3 year warranty parts and labor. So If that's a case You should call Pentair and ask for Knowledgeable warranty technician to look at your heater. If you have any questions please ask. I do a lot of warranty work for Pentair and work for a Pentair dealer.
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Bob,

    I'm pretty new to pool equipment but I've done heat transfer and pipe sizing calculations for decades. For normal installations and gas systems you should have sufficient flow with 1-1/4" schedule 40 pipe. It could be close with all your other home gas consuming appliances on at once but not if they are all off. I'm assuming you've checked this out and it still cycles when you verify only pool heater is running? That being correct I like to trouble-shoot the safety stuff followed by the simple stuff first. So here's what I'd do, in order:


    1. You've probably already done this but to be sure and safe I've included this. Make sure there's no gas leak in the system. You indicated there's a gas smell when the unit runs. Is this only in the exhaust air while running? If not you have a gas leak. You can usually get your gas company to check this for free.
    2. Double check to be sure the line run to your heater is 11/4" and not reduced where it tee's off of the main line.
    3. Check to be sure the installer did not use flex pipe to make the final connection to your heater. That's a big no-no for most high btu demand devices like pool heaters.
    4. As RedBlue mentioned previously check the model number to be sure it's for natural gas not propane.
    5. Make sure your water pressure is not dropping too low due to a clogged water filter. Mine has a water pressure sensor on the inlet to sense water flow. If you're not sure about this by-pass the filter and see if the frequent heater cycling stops.
    6. When your heater shuts down it should have an indication of what caused the problem with an error coded or a blinking light. Find out what your code is. Could be the air flow through the burner. On mine (Jandy) I got an indication of "Check Ign Steps". Turned out it was a loose wire on one of the pressure sensors. A leaf over the fan inlet can cause the same error.
    7. If all the above check out, I'd call a qualified technician and request a tech that knows how to use a manometer to check pressure. This is waay cheaper than a $3000 line. Have him measure the pressure while the unit runs to check that the pressure is indeed too low when it shuts down and it's not a calibration issue with a sensor inside the heater. Please don't try this yourself unless you're really qualified to work with gas.


    I hope this helps and please let us know what you find out.

    Chris
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    Re: Pentair mastertemp 400 cycling due to low gas flow?

    Here's some photos of the system.




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