Case study to determine root cause of Pentair mastertemp 400 not igniting

[JoyfulNoise]

So 8.0" can be ok;
how about flow? Im not sure how to read the specs of the regulator picture I posted
Its an S102, 3/16" Orifice, 5.5-8.5" WC range, and 1-86?
btw, thanks a ton for all your help thus far!

A 3/16” orifice is pretty small. If you randomly look up natural gas regulators with their spec sheets, a 2 psi inlet pressure with a 7” WC outlet pressure and a 3/16” orifice only yields less than 300 scf per hour for most reasonable pipe diameters (3/4” to 1-1/4”). I think you’re going to have to bring this issue up with the gas company and just make sure they understand that you have a pool heater which, all on its own, needs 400 cf per hour of gas. So they need to size the meter and regulator accordingly.

 

[Asherk74]

A 3/16” orifice is pretty small. If you randomly look up natural gas regulators with their spec sheets, a 2 psi inlet pressure with a 7” WC outlet pressure and a 3/16” orifice only yields less than 300 scf per hour for most reasonable pipe diameters (3/4” to 1-1/4”). I think you’re going to have to bring this issue up with the gas company and just make sure they understand that you have a pool heater which, all on its own, needs 400 cf per hour of gas. So they need to size the meter and regulator accordingly.

Thank you so much!
I will def push this point across, also, it seems like the regulator was built dated stamped for 1-86 (I.e. 35 years old, should they be replaced at some point)

 

[JamesW]

Pressure could be anywhere from a ½ pound to 60 psi before the service regulator.

Typical pressure is 15 to 60 psi.

The pressure coming out of the regulator going into the meter can be anywhere from 5.5 to 8.5" wc.

The meter produces a 1/2" wc drop in pressure at 400 CFM.

If the pressure going into the meter is 8" wc, the pressure coming out will be 7.5" wc at 400 CFM.

If the pressure drop at the heater is 2" wc, then the dynamic at the heater should be 5.5" wc.

I would want a minimum of 5" wc at the heater.

 

[JamesW]

If the dynamic pressure at the heater is less than 5.5" wc, I would suggest that you change to a 2 psi service regulator so you will have 2 psi coming out of the regulator going into and out of the meter and then 2 psi to the heater where you will put another regulator immediately before the heater to drop from 2 psi to about 7" wc.

You would also need a regulator after the meter on the line going into the house to drop from 2 psi to 7" wc before going into the house.

I would change the meter to a bigger size to accommodate the full flow required by the heater and everything else that can run at the same time.

 

[Asherk74]

Manometer came, so more Data points!
Hooked up high-low side as shown in the pentair manual.
Im am assuming this will then measure static (pre ignition) and dynamic (ignition) pressures?
Pre-ignition I am measuring ~3.75"WC, never touches 4" (the min), after ignition it drops to ~2.1" or so and ignition shuts off. I can safely assume there is not enough pressure/flow reaching the heater?
New finding: there def is ignition, some cycles last for a few seconds and with the top off I can hear the flame and feel the heat.

 

[JoyfulNoise]

Yep. Supply pressure is way too low. At least now you can tell the gas company tech exactly what numbers you’re seeing. They aren’t allowed to work on anything but their own equipment but if you can tell him where the heater is at, he can try to adjust his equipment to compensate.

 

[JamesW]

High/low is for the manifold.

To test the inlet gas pressure, you only use the single test.

 

[JamesW]

Below is the test for the manifold pressure.

To test the inlet pressure, you don't use both ports; you only use the Positive (High Pressure Port).

 

[JamesW]

The first picture is the inlet tap.

The second picture is the manifold tap.

Just use the inlet tap connected to the positive port.

 

[Asherk74]

Thanks! That makes more sense, but leads to a more depressing test result:
Starting (static) pressure: 8.3”
After ignition (dynamic): -1.5” !! so it ‘loses’ about 10” of pressure!
2 seconds later flame shuts off and pressure climbs back to 8.3”.

 

[JoyfulNoise]

That’s a huge pressure drop. As @JamesW alluded to, you need a drip leg on your plumbing to the heater. If the gas company says you’re ok or upgrades your meter and you are still getting a huge pressure swing like that, then I’d be concerned that your gas line or gas valve has some kind of obstruction in it. Let’s see what the gas company comes up with.

 

[JamesW]

That indicates that there is some sort of blockage in the line or maybe a valve is closed.

Have the gas company check their equipment, but it seems like the gas line going to the heater is probably defective somehow.

There is a screen in the valve inlet which might be clogged due to the lack of a drip leg, which is used to collect particles in the gas line.

Check the screen on the inlet of the valve.

Maybe the gas line can be blown out to make sure that it is not clogged with water or debris.

 

[JamesW]

In the below case, there was a bad valve going to the heater gas line.

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...

www.troublefreepool.com

 

[JamesW]

You have a valve on each end of the gas line and one might be defective.

Get someone to take it apart and check the valves and add a drip line to the plumbing near the heater.

 

[jedigrover]

Make sure you don't have something like this:

 

[Asherk74]

All right guys, next update !
SoCal gas tech came; my pressure is maxed out legally (~9"), replaced regulator with a new 1/4" orifice , then measured 8.7" at meter and 8.3" at heater.
He said flow 'sounded' wimpy at the heater but strong at meter.
After he left I decided test flow using meter gauge at
A. heater gas pipe at METER, I did this by loosening the union so gas can escape somewhat:

B. opening up the gas line at heater and watch flow (had a helper turn on and record flow):

In short: the flow reaching the heater is a fraction of the flow coming out of heater when the union is opened.
This points to a clog in the line? We did not hear any signs of water. can a plumber use a camera to look for blockages, and if so can they be 'blown out'..
see attached pics and videos
Thanks guys, you've really been invaluable!

 

[JoyfulNoise]

There’s a blockage somewhere. Perhaps the buried line is compromised in some way. You probably need to call in a certified gas plumber and see if they can scope the line out.

 

[jedigrover]

Yeah, you've got a problem between the meter and heater. Need a plumber to check it out. Might be able to blow it out. I don't know if they'd have a scope small enough to look down the line.

 

[JoyfulNoise]

Question - you bought this house with the pool … did the previous owner have a heater? We’re there any disclosed problems with the gas line?

 

[Asherk74]

Question - you bought this house with the pool … did the previous owner have a heater? We’re there any disclosed problems with the gas line?

They had a 400k heater, but was likely original from 1987 without new air/fuel/pressure safety controls I presume. So it did turn on during inspection, but i'm now guessing barely functional.
We bought new heater and had it installed last summer when we moved in.
nothing was disclosed to us