Natural Gas Heater manifold problem..

RichRodgers

Member
Jul 18, 2020
6
West Linn, Oregon
I've recently replaced my Hayward H400FD gas heater with a newer model (old one about 15 years old). Everything seems to be working, but often won't start. Input pressure is 6.6 to 6.9, well within the 4.5 to 10.0 recommended pressure. Manifold pressure is 1.32, well below the 1.8 to 2.0 recommended pressure. I'm fairly certain this is causing the starting problems, and would be an issue either way.

My problem is that I can turn it down at the far height of the screw distance to about 1.10 when the heater turns off. No matter how far down I turn the screw clockwise, it will quickly hit 1.29-1.34 and just bounce around that range. Fairly certain the new unit has a defective Honeywell valve, but thought I'd check here to see if anybody has advice.

The only thing "unique" about the install is that i did have to turn the 90 degree elbow at the top of the valve to match the right side input of the older installation. Since the input pressure is perfect I doubt this is causing issues though.

Probably not useful, but when the heater does start, the input pressure tap does go from 6.6 to 2.4. This value is not variable either as I turn the Regulator Adjustment screw. I'm assuming this is standard as the manifold kicks in, but could be a sign of something?
 

JamesW

TFP Expert
Mar 2, 2011
21,547
The pressure should not drop more than about 0.5 inch w.c from static to load and it should never drop below the inlet rating of 4.5 inch w.c.
 

RichRodgers

Member
Jul 18, 2020
6
West Linn, Oregon
The pressure should not drop more than about 0.5 inch w.c from static to load and it should never drop below the inlet rating of 4.5 inch w.c.
Thanks again James, I kinda figured about the 4.5" lower rating but wasn't positive and had no clue on the 0.5 inch. static to load. I'm guessing at this point that some of the old piping has a leak and will be testing down the line to check. Hopefully there won't be a next time, but I'll definitely check first if I have to replace it again ;)
 

RichRodgers

Member
Jul 18, 2020
6
West Linn, Oregon
The input pressure is dropping too much, which indicates a problem with the gas supply.
Tested older connections with soap solution purchased at store, no leak.
Resealed and tightened older connections. Tested older connections with soap solutions, no leak.
Old heater worked fine, but could be less particular.

Old heater did not have the blower, but inside connection is exactly as it was, only unscrewed the connection at the valve and moved to new heater. I'm a bit concerned about the transition from 3/4" to 1/2" and then back, but that is how it was originally connected.

Gas pipe runs along side of the house about 20 feet, comes down three feet then over to heater. Inside heater looks like this:

Heater.jpg

Any thoughts? Thanks..
 

JamesW

TFP Expert
Mar 2, 2011
21,547
The line should not go down to 1/2”. Also, Flex line is usually not acceptable as specified in the installation manual.

Are all of the gas valves on? There might be one near the meter. There should be one near the heater. There’s the one in the heater.

What size is the Meter? The meter model number from the data plate should be the cubic feet per hour. 1 cubic foot = 1,000 btu per hour.

For example, a 250 meter will do 250,000 btu/hr. A 400 cubic foot meter will do 400,000 btu/hr etc.

Your meter should be at least a 400 model or bigger depending on what other gas appliances might run at the same time.

What size is the gas line from the meter to the heater?
 

RichRodgers

Member
Jul 18, 2020
6
West Linn, Oregon
The line should not go down to 1/2”. Also, Flex line is usually not acceptable as specified in the installation manual.

Are all of the gas valves on? There might be one near the meter. There should be one near the heater. There’s the one in the heater.

What size is the Meter? The meter model number from the data plate should be the cubic feet per hour. 1 cubic foot = 1,000 btu per hour.

For example, a 250 meter will do 250,000 btu/hr. A 400 cubic foot meter will do 400,000 btu/hr etc.

Your meter should be at least a 400 model or bigger depending on what other gas appliances might run at the same time.

What size is the gas line from the meter to the heater?
I swear, the prior home owner had an idiot brother-in-law that did construction, this house has so much done wrong...

The meter is Class 175-250. The piping is 1" from the meter to about 18" from the heater. At that point it goes from 1" to 3/4" and has a valve. There is a "T" connection near the meter and a shutoff valve there as well. I had previously turned those off, and then on again and made sure they were full on. So three valves total, but all three are on when I try to run it.

I suspect I need to get the gas company out and get a higher than 400 class meter (gas stove / water heater / heater), then remove the flex line and replace with 3/4" pipe. Likely time to bring in a professional... should I look for a plumber that does water heaters, an HVAC or... ??
 

RichRodgers

Member
Jul 18, 2020
6
West Linn, Oregon
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