JXi Gas Fired Pool heater 400 reading Negative 1.7" WC when it turns on

[McKinney]

So four weeks ago we had a Jandy JXi installed at the house. At that time they also needed to install a new gas valve? It looks like it throttles gas to the heater in line not inside the equipment. Anyhow, after they come back and install that they say it works. Well I try it the next weekend and it doesn't want to light. They com back out while I am not here with a Jandy rep. They say it is the gas pressure to the unit. They have a video showing a meter that goes from 17"WC to -1.7 "WC.

I just need someone to tell me what this means. I understand something about pressure. But what I think this means is that I have a volume issue, as in, there is not enough volume of gas for this unit to use and therefore we are creating a vacuum.

My next question is how can the gas company fix this? Before I start calling and making a whole lot of mistakes I'd like to get some understanding of what I need to say and what words will be useful when dealing with them.

Thanks

 

[ps0303]

Did they have to upgrade your gas meter and install a regulator at the outside of the heater? Guessing the regulator is what they meant when you said gas valve.

Where are they taking the reading to show the 17"WC? That is way too high. Here are what the heater needs per the the manufacturer. As you can see the max inlet, coming from your gas companies meter, is 10" WC, minimum is 4"WC The reading as the manifold inside the heater should read .2"WC coming out of the gas valve when it fires up.



Who installed the pool heater? Are they gas licensed? If so they should be able to adjust the regulator to bring the pressure down going into the heater. Unless of course your local gas company prefers they do it.

 

[McKinney]

I completely agree with you. Which is why I posted here first. I had an authorized dealer to the installation and setup. They did install a new regulator. The problem is that after the heater turns on it goes from 17 WC to negative 1.7"WC.

How does it go negative?

 

[ps0303]

In the picture I attached above, the pressure coming from the regulator to the heater needs to be between 4.0"WC and 10"WC. If they measured it coming out of the regulator at 17"WC, it is too high and needs to be lowered to between 4"and 10"WC. Now the reading on the gas valve inside the heater, if you measure the pressure on what is called the "manifold" side, that is where the gas exists the valve and to the burner, it should a -0.2"WC.

**I updated this as the first manual I looked at did not have the correct reading for the manifold pressure. As you can see, I posted a picture from a manual and it does NOT list it as a -0.2WC

 

[JamesW]

The correct manifold pressure is -0.2" when measured against the reference of the line going from the gas valve vent to the blower inlet.

Since the blower inlet will have a negative pressure (below ambient atmospheric pressure), measuring the manifold vs air will be even more negative than -0.2.

-0.2 is listed as the offset pressure on the label inside the heater. The maxetherm also uses a negative manifold pressure of -0.2 as it's the same design.

Part of the manual does say 0.2, but it's a typo. The "-" is missing. Later in the manual, the correct pressure is shown.

4.3 Gas Offset Pressure Test
Before operating the heater it is necessary to test the offset gas pressure to ensure that it falls within the required range of -0.2" WC (Inches Water Column) +/- 0.1" WC. This reading must be taken with the heater
running using a digital differential manometer

In any case, I think that the inlet pressure is too high and that there is a supply issue, either the lines are too small or there is a restriction.

The outlet of the gas valve goes to the inlet of the blower. The inlet of the blower is under vacuum, which sucks the gas out of the gas valve. The outlet pressure of the gas valve is actually less than -0.2 with respect to the air. It's -0.2 with respect to the outer inlet of the blower.

Since you're getting pressure and then vacuum, the line probably has a serious blockage or some other supply issue.

It might be as simple as a valve that is closed or almost closed.